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SPOC PWM SPI Dr iver P W M G e n e r a t i o n t h r o u g h S P I u s i n g S P O C d e v i c e s o n X C 2 0 0 0 F a m i l y ( F o r i n t e r n a l u s e o n l y )

App l i ca t i on No te , V1 .0 , May 2008

AP16143

Edition 2008-05-21 Published by Infineon Technologies AG 81726 München, Germany © Infineon Technologies AG 2008. All Rights Reserved.

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AP16143 Driver API for PWM Generation over SPI

Application Note 3 V1.0, 2008-05

AP16143 Revision History: 2008-05 V1.0 Previous Version: none Page Subjects (major changes since last revision) 1.0 * Accept review from Fabian Gressel

* Cross-references to document “PWM operation using the SPI for SPOC product family” (Olivier Ploix)

0.2 Second draft version * Replaced: time unit us with us, and other typos * Updated: Motivation and Requirements (Chapter 3) * Updated: SPOC PWM Driver API (Chapter 6) * Added: Sample Project #2 with XC2287 Power EasyKit (Chapter 9) * Added: API function execution time (Chapter 10) * Added: Brightness Control use case (Chapter 11)

0.1 Initial draft version

We Listen to Your Comments Any information within this document that you feel is wrong, unclear or missing at all? Your feedback will help us to continuously improve the quality of this document. Please send your proposal (including a reference to this document) to: [email protected]


Table of Contents Page

Application Note (For internal use only) 4 V1.0, 2008-05

1 Scope...........................................................................................................................................6 2 References ..................................................................................................................................7 3 Motivation and Requirements....................................................................................................8 3.1 Motivations ...................................................................................................................................8 3.2 Requirements ...............................................................................................................................8 4 Infineon’s SPOC Family Devices...............................................................................................9 4.1 Controlling Mechanisms .............................................................................................................11 4.2 Daisy-chain SPOC......................................................................................................................12 5 PWM Generation over SPI for SPOC-Family...........................................................................13 5.1 Device Organization ...................................................................................................................13 5.2 PWM Generation Limits..............................................................................................................13 5.3 Generation Method.....................................................................................................................14 5.4 Generation of PWM with fixed-time SPI commands ...................................................................15 5.5 ADC Multiplexer command insertion...........................................................................................16 5.6 General Architecture for PWM generation with fixed-time SPI ....................................................17 5.7 Method to avoid PWM Jitter........................................................................................................18 6 SPOC PWM Driver API .............................................................................................................19 6.1 Limitations ..................................................................................................................................19 6.2 User-defined properties ..............................................................................................................19 6.3 Group Period and Period Divider ................................................................................................20 6.4 A/D conversion result..................................................................................................................21 6.5 SPI Standard Diagnostic Data ....................................................................................................21 6.6 State Machine.............................................................................................................................21 6.7 Data Structure ............................................................................................................................21 6.8 File descriptions and dependencies............................................................................................22 6.9 Pre-compile Configuration ..........................................................................................................23 6.9.1 TSpocConfig structure ................................................................................................................24 6.10 Type definitions ..........................................................................................................................24 6.10.1 TSpocGroup ...............................................................................................................................24 6.10.2 TSpocChannel............................................................................................................................25 6.10.3 TSpocPeriod...............................................................................................................................25 6.10.4 TSpocChannelDef ......................................................................................................................25 6.10.5 TSpocDelayData ........................................................................................................................25 6.10.6 TSpocGroupConfig .....................................................................................................................26 6.10.7 TSpocConfig...............................................................................................................................26 6.10.8 TSpocCommandBuffer ...............................................................................................................26 6.10.9 TSpocDiagnosticData .................................................................................................................27 6.10.10 TSpocChannelData ....................................................................................................................27 6.10.11 TSpocGroupData........................................................................................................................27 6.10.12 TSpocGroupDuty........................................................................................................................28 6.11 Exported Variables .....................................................................................................................28 6.11.1 SpocGroupCount ........................................................................................................................28 6.11.2 SpocGroups................................................................................................................................28 6.12 Public function prototypes...........................................................................................................28 6.12.1 Spoc_Init.....................................................................................................................................28 6.12.2 Spoc_SetDutyCycle....................................................................................................................29 6.12.3 Spoc_SetDutyCycleAll................................................................................................................29 6.12.4 Spoc_SetGroupPeriod................................................................................................................30 6.12.5 Spoc_IsBusy...............................................................................................................................30 6.12.6 Spoc_GetAdcValue ....................................................................................................................30 6.13 Interrupt Service Routines ..........................................................................................................31 7 Implementation in XC2000 Microcontroller Family ................................................................32 7.1 Unique hardware features ..........................................................................................................32


Table of Contents Page


7.2 Hardware Resource Mapping .....................................................................................................32 8 Sample Project #1 with XC2286M EasyKit ..............................................................................35 8.1 Required Equipments .................................................................................................................35 8.2 Required PC Software ................................................................................................................35 8.3 Pin Assignment...........................................................................................................................35 8.4 Project Files................................................................................................................................36 8.5 SPOC Driver Configuration.........................................................................................................37 8.5.1 Pre-compile parameters .............................................................................................................37 8.5.2 TSpocConfig structure values.....................................................................................................38 8.6 Shell operation............................................................................................................................39 9 Sample Project #2 with XC2287 Power EasyKit .....................................................................41 9.1 Required Equipments and Software ...........................................................................................41 9.2 Pin Assignment...........................................................................................................................41 10 XC2000 CPU Performance .......................................................................................................42 10.1 TX-FIFO Interrupt .......................................................................................................................42 10.2 SPI-RX and ADC Diagnostic Interrupts.......................................................................................43 10.3 API Functions Execution Time....................................................................................................43 11 Brightness Control (use case).................................................................................................45 11.1 Lookup Table..............................................................................................................................45 11.2 Control Routine...........................................................................................................................47 11.3 CPU Load...................................................................................................................................47


Scope


1 Scope

Dear Reader,

Thanks for your interest to the PWM generation over SPI system using SPOC devices! Almost all car OEM’s require PWM-control for lighting applications today. PWM control ensures constant brightness for loads like LEDs or bulbs with voltage range from 9 to 16 Volts.

This document focuses mainly on software driver API and implementation example in XC2000 microcontroller family, i.e XC2287 and the new middle-range device XC2286M.

Chapters 3 until 5 contain of the motivation and principles of described in the reference document [2] “PWM operation using the SPI for SPOC product family”. For those readers who are already familiar with it may jump directly into chapter 6 SPOC PWM Driver API.

Have fun with Infineon’s SPOC Driver and Devices!


References


2 References [1] SPOC Product Information Page, http://www.infineon.com/spoc

[2] Olivier Ploix. “PWM operation using the SPI for SPOC product family” (Spoc PWM Rev 1.0.pdf). Automotive Power. Infineon Technologies. September 2007.

[3] XC2000 Device Family User Manual. XC2200_um_v2.0_2007_12_vol1_sys/per.pdf


Motivation and Requirements


3 Motivation and Requirements

3.1 Motivations

Almost all car manufacturers today require PWM-control for lighting application, e.g. driving bulbs or LEDs. The reasons for using PWM are: • Increased bulb lifetime, e.g. 5% over voltage leads to 50% less lifetime for the bulb. • Constant brightness • CO2 reduction • Optimized EMC behavior. Every channel can be started at dedicated time (PWM phase shift)

3.2 Requirements For automotive lighting application there are two typical requirements. 1. Bulb application

• PWM frequency from 50 Hz up to 200 Hz • Duty cycle from 0% up to 100% • Precision: 0.5%

2. LED application

• PWM frequency from 100 Hz up to 400 Hz • Duty cycle from 0% up to 100% • Precision: 0.5%

T : PWM period thigh : on time tlow : off time Duty cycle (in %) = (thigh / T ) x 100

Figure 1 Standard PWM Signal


Infineon’s SPOC Family Devices


4 Infineon’s SPOC Family Devices SPOC Family is a family of multi-channels high-side switches for Advanced Light Control developed by Infineon. Currently there are several devices available. They are especially designed to control standard exterior front and rear lighting in automotive applications.

Figure 2 shows typical diagram of a SPOC device, e.g. 2nd generation SPOC BTS5682E with 6-channel switches device with LED mode and cranking option.

Figure 2 Block diagram of SPOC-II BTS5682E with 6-channel switches device

Features of such a SPOC device are: • N parallel inputs • SPI configurable device • configurable LED mode for identical hardware design at Tier-1 • cranking (on some channels) • current limitation • limp home control (LHI)

Typical application using discrete solution is shown in Figure 3.




Figure 3 Example of lighting application with discrete solution

With SPOC-Family, we can get an integrated solution as shown in Figure 4.

Figure 4 Example of lighting application with integrated solution1

Immediately, there can be seen benefits of using the SPOC-Family devices.

1. Benefits for PCB

• Less traces

1 High beam is not considered.




• Less parts • Less area

2. Benefits for Microcontroller

• Less IO pins • Less AD channels (due to multiplexed sense output of SPOC devices) • Diagnostics through SPI reception.

3. Scalability with one PCB design

• LED or Bulbs application with the same device (differs only at the PWM duty-cycle strategy) • Pins, functions, and package compatibility within SPOC family • watchdog option

4. Assembly cost and quality

• Less part reference management • Less pick and place • Less testing • Less parts decreases the risk of reliability issues linked to soldering

4.1 Controlling Mechanisms

A SPOC device can be driven either by: • Direct inputs (IN0...INx) • SPI input.

In direct inputs method, the inputs shall be connected to PWM generator of the microcontroller, e.g. digital-level PWM signal generated by CAPCOM peripherals. The output will have the similar PWM pattern raised to the battery voltage level, plus with additional switching on/off time and delay.

Figure 5 shows an example of two SPOC devices (total 10 channels) with direct input for PWM mode: • processor needs to use one PWM generation peripheral (e.g. CAPCOM) for each channel • in the case different PWM patterns for each outputs, probably there will not be enough

microcontroller’s hardware resources. In SPI input method, as shown in Figure 6, SPOC devices will operate to switch on or off the load or delivers diagnostic data based on the given SPI command. In the case of PWM generation, the commands shall be prepared by software and sent through the SPI line. This solution can provide more efficiency concerning cost and IOs.




Two most used SPI commands for controlling SPOC devices are the OUT and DCR commands. OUT command has the bitfield control of the output. Writing a ‘0’ value at the channel’s bit switches off the output and writing ‘1’ otherwise. DCR command contains bitfield to select the output of ISense signal from SPOC device, which can be sampled by A/D converter of the microcontroller to represent the status of output current of a channel.

Figure 5 Controlling SPOC devices with direct input

Figure 6 Controlling SPOC devices with SPI input

4.2 Daisy-chain SPOC The SPOC-Family allows also daisy-chaining of several devices in one SPI line, as shown in Figure 6. With this feature, more channels can be controlled by one SPI line.


PWM Generation over SPI for SPOC-Family


5 PWM Generation over SPI for SPOC-Family

5.1 Device Organization

One microcontroller may have more than one SPI communication interface and in each SPI interface we can assign one or more daisy-chained SPOC devices, which we call a SPOC group. The Number of SPOC groups supported by a microcontroller depends on CPU speed, interrupt capability and other available hardware resources.

One ADC input for each group is needed to measure the current sense (ISense) value. The output multiplexer from a SPOC device can be selected to high impedance (tristate) so we can combine all ISense output of the devices of the group into one ADC input. The selection can be done in timeslots.

Figure 7 SPOC Devices Organization in Groups

5.2 PWM Generation Limits

In order to properly use SPOC-Family for PWM generation over SPI, some parameters shall be carefully considered. The maximum PWM resolution is limited by:

• number of SPOC devices in daisy chain • minimum delay between SPI frames due to processor or SPI peripherals performance • A/D conversion method




CS

SCLK

SI

tCS(lead) tCS(td)tCS(lag)

tSCLK(H) tSCLK(L)

tSCLK(P)

tSI(su) tSI(h)

SO

tSO(v)tSO(en) tSO(dis)

0.7Vdd

0.2Vdd

0.7Vdd

0.2Vdd

0.7Vdd

0.2Vdd

0.7Vdd

0.2Vdd

SPI Timing.emf Figure 8 SPI message frame (digital signal)

From Figure 8 we can calculate framet , i.e. total time needed to transmit one SPI command frame for SPOC devices in daisy-chain:

)()()((max) ldCSlagCSSPOCbit

leadCSframeres ttBaudrate

NNttt ++

×+==

framet is also the maximum resolution time, (max)rest , when delay between sending two frames (interframe delay) is 0.

As example, for a SPOC II product, the following SPI parameters can be used:

• bitN = 8-bit

• Baudrate (maximum SPI frequency) = 2MHz • )(leadCSt (minimum slave select lead-delay) = 1us

• )(lagCSt (minimum slave select trailing-delay) = 1us

• )(ldCSt (minimum slave select delay) = 2us Following table shows minimum duty cycle due to minimum resolution time for different number of SPOC devices in daisy-chain and maximum output PWM frequencies.

N SPOC tres(max) fpwm = 50Hz fpwm = 100Hz fpwm = 200Hz fpwm=400Hz 1 8 µs 0.04% 0.08% 0.16% 0.32% 2 12 µs 0.06% 0.12% 0.24% 0.48% 3 16 µs 0.08% 0.16% 0.32% 0.64% 4 20 µs 0.10% 0.20% 0.40% 0.80%

However, the overall minimal duty-cycle will be higher if we consider also switching time of the output MOSFET’s and the time for A/D measurements.

5.3 Generation Method

There are two foreseen PWM generation methods over SPI:




1. Sending SPI commands at every expected edge of PWM signal.

2. Sending SPI commands at every fixed time, i.e. equals to PWM resolution time.

Comparison of both methods can be seen in the following table.

Method 1: Method 2: Advantages

• Low bus load • Less RAM usage

• Less timer and hardware usage • Feasible, simple and easy

implementation in microcontrollers such as the XC2000 Family

Disadvantages

• Higher interrupt load due to different

timings of every command and channel • Possible jitter due to interrupt blocking

from other CPU task • Higher usage of hardware resources

• Bus load • RAM usage

5.4 Generation of PWM with fixed-time SPI commands

In this application note, we only describe and implement method 2, as shown in Figure 9.

For example, to achieve 0.5% precision, 200 SPI commands are needed per PWM period. With 400Hz PWM frequency (T = 2.5ms), the SPI commands are sent each every 12.5us. All channels in the same group, i.e same SPI line, will have the same basic frequency. In addition, processor can calculate custom pattern to generate more PWM within the 200 SPI commands but with less precision, e.g. as shown by CH4.

The red dashed line shows offset relative to CH0 in order to generate phase-shifted PWM for other channels.




Figure 9 PWM generation by sending SPI frames at fixed-time

5.5 ADC Multiplexer command insertion

In this application PWM signals are generated with different frequency and starting point. A user-defined phase-shift is applied to every next channel. A/D measurement is needed to monitor whether the load is switched properly. Two different A/D measurement approaches can be done: 1. At specific time after active level 2. At specific time before passive level

Because of simplicity, the first approach will be used.

Figure 10 PWM generation by sending SPI frames at fixed-time




Here the ADC multiplexer command for a PWM channel is inserted right after the “ON” time of that channel. In some cases, we can also delay the ADC mux command to a later time due to rise time of the high-side switch and multiplexer switching delay, but this will increase the minimum duty cycle, e.g. from 0.5% to 1%.

In Figure 10 example, ADC is triggered every fifth SPI commands to wait the stable output of PWM signal. But this also will increase the minimum duty cycle, traded with less RAM required to store the A/D conversion results.

Given we have a number of SPI command buffer (SPOC_BUFFER_LENGTH) and the timer tick period (K) to trigger the ADC, then A/D conversion result buffer size is:

The minimum duty cycle will be increased by K times the original PWM resolution1 because we can not switch off the PWM output before the A/D conversion is done.

5.6 General Architecture for PWM generation with fixed-time SPI The architecture for generation of PWM with fixed-time SPI commands is shown in Figure 11. The use-cases represent the typical cases needed from the SPOC’s user point of view: • SetDutyCycle: to change duty cycle of output PWM signal of specific channel. This is done by

calculating SPI command pattern to be transmitted in the command buffer (RAM). • SetGroupPeriod: to change or to set the period of all PWM signals. This is done by changing the timer to

trigger transmission of each SPI command. • GetDiagnostic: to read diagnostic data from SPOC device • GetAdcValue: to read A/D conversion values which represent the ISense of the PWM channels Operation of the SPOC can be fully independent from the User Actions. For each SPOC group, there are common hardware and software requirements:

1. Three buffer areas needed:

• For calculated PWM and diagnostic MUX pattern • For SPI-received diagnostic data • For AD conversion results

2. Three interrupt handlers: • For handling sending of commands (TX) • For handling reception of diagnostic data (RX) • For handling AD result

3. One timer for fixed-time triggering SPI transmission 4. One timer for triggering AD conversion based on SPI transmission The timer periodically triggers at fixed-time the transmission of each SPI command. The SPI transmitter circularly reads the command patterns from command buffer in the RAM. At the same time, the trigger is forwarded to start A/D conversion. With the normal behavior of SPI communication and SPOC device, each transmitted command is exchanged with a diagnostic data sent by the SPOC device which can be stored by the SPI receiver into the RAM.

1 Calculation of PWM resolution is explained in Section 5.2 “PWM Generation Limits"




Figure 11 General architecture for PWM generation by sending SPI frames at fixed-time

5.7 Method to avoid PWM Jitter

In the above architecture, the output PWM can have a jitter. This happens when the SPI transmits a command too late because the TX FIFO is empty. Therefore, to avoid jitter: • There shall be no SW task which blocks or disables interrupt service routines • TX interrupt priority should be set high enough.


SPOC PWM Driver API


6 SPOC PWM Driver API

6.1 Limitations

This specification is based on requirements described in document [2] (explained also in chapters 3 until 5), but with the following limitations: 1. Maximum only two daisy-chained devices allowed in one SPOC group. This implies:

• usage of 16-bit SPI frame to control two daisy-chained group devices, or 8-bit SPI frame to control one

• usage of 16-bit data element for the SPI command buffer 2. The focus is on PWM generation over SPI, ADC diagnostic, and receiving of SPOC standard diagnostic

data. Other SPOC control and diagnostic command is not yet supported. On the other hand, there is no API limitation on the number of groups controlled by one microcontroller because it purely depends on the capacity of microcontroller.

6.2 User-defined properties

In general, we define several properties for configuration and run-time purpose. Some of these parameters are contained in the TSpocChannelDef structure and TSpocDelayData.

SPOC_BUFFER_LENGTH is length of RAM buffer used to store PWM pattern. This value equals to the maximum period PWM signal and equals also to the maximum PWM Duty in terms of “frame tick” represented by FrameIndex.

Because all channels will have a different phase, an Offset to the beginning of the buffer is needed for each channel. Command for the ADC multiplexer for a channel is inserted directly after the start of PWM phase (at Offset+1).

It is important to note that the period or frequency of a group is changed by changing the delay between SPI frames (interframe-delay)

The A/D conversion results are not stored at every slot of SPI transmit, but prescaled with SPOC_ADC_TRIGGER_COUNT. This leads to:

SPOC_ADC_BUFFER_LENGTH = (SPOC_BUFFER_LENGTH / SPOC_ADC_TRIGGER_COUNT)

There will be several A/D samples available for each channel, but user can define in which position Spoc_GetAdcValue() shall read the correct A/D sample, defined by AdcOffset and AdcOffsetB.


SPOC PWM Driver API


Figure 12 Properties of PWM Generation

6.3 Group Period and Period Divider

Group period or frequency can be changed by calling Spoc_SetDutyCycle() function. This function sets new SPI interframe delay to extend the PWM period corresponds to the requested frequency.

With PeriodDivider = 1, a PWM channel will run at the same group period or group frequency. Furthermore, PWM frequency of a channel can be multiplied by dividing the group period. This is simple by generating more pulses into the RAM buffer. For example, if the SPOC group runs at 100 Hz, setting channel’s PeriodDivider = 4 will produce channel frequency 400 Hz at that channel.

After Spoc_Init(), all channels will have PeriodDivider = 1. At run-time, PeriodDivider (PD) can be set by calling Spoc_SetDutyCycleAll() function.


SPOC PWM Driver API


Figure 13 Channels with different duty and period

6.4 A/D conversion result

It is up to the user how the data is going to be read. User can directly read the ADC data by Spoc_GetAdcValue() function, which contains value of the ADC result buffer at index = AdcOffset + AdcOffsetB.

Alternatively, direct access to the ADC result buffer is possible by using exported variable SpocAdcResults.

For the case of XC2000 Family device, SpocAdcResults is copied directly from ADC result register. In this register, only 10-bit contains the conversion value (bit 11… 2), therefore: AdcValue = (SpocAdcResults[GroupNr][index] >> 2) & 0x3FF

6.5 SPI Standard Diagnostic Data

The SPOC standard diagnostic data can be accessed directly through the exported variable SpocGroups, e.g. SpocGroups[GroupNr].Diagnostic.Data[RxIndex]

6.6 State Machine

After power-on reset, the hardware is typically in uninitalized state. Some variables are initialized in the microcontroller start-up phase, i.e. c_init() function. But in general, the driver is considered as not initialized. Only after calling Spoc_Init() function with proper configuration, the driver enters initialized state (READY).

Figure 14 SPOC driver states

Duty cycle of a channel can be changed by calling Spoc_SetDutyCycle() function. This function calculates new SPI pattern for the requested duty cycle. At the end of pattern calculation, a SPOC_NDAT flag is set to tell the transmit interrupt service routine (TX ISR) to consider the existence of new SPI pattern. Before the TX ISR reads out and takes the new data into operation, the driver is in BUSY state

6.7 Data Structure

Following diagram (in UML class diagram notation) illustrates the minimum description of one SPOC group’s data structure. Detailed description in C can be found in Section 6.10.11, TSpocGroupData.


SPOC PWM Driver API


Figure 15 Driver’s Data Structure

6.8 File descriptions and dependencies File Purpose Spoc.h Header file for user or application file

Spoc.c Implementation of: • core functionality • initialization of SPI / USIC hardware, which also calls initialization of ADC,

CCU6, Port Pins, and interrupt control Spoc_int.c/h Implementation of interrupt service routines and interrupt controller.

Spoc_adc.c/h Implementation of: • initialization of ADC hardware • initialization

Spoc_cfg.c/h Implementation of configuration data which is passed into Spoc_Init.

The SPOC driver is implemented in several C-source files and depends on several other files from other hardware drivers. But in general, it is enough for user or application files to include one header file, i.e. Spoc.h. In addition, for different SPOC devices or groups set-up using the same microcontroller platform, configuration files Spoc_cfg.h and Spoc_cfg.c are needed.


SPOC PWM Driver API


Figure 16 SPOC driver file dependencies

In the driver layer, there are generic files and “project specific files”. Generic files are files which shall be used as it is. Project specific files are files which might need to be modified according to the project requirements.

6.9 Pre-compile Configuration

Pre-compile configurations are set before compilation of the driver. These parameters are implemented as #define and stored in Spoc_cfg.h file.

Name Description Range/Values

SPOC_MAX_GROUPS Maximum number of groups supported by the driver

1..n

Typically 2.

SPOC_DEVICES_PER_GROUP Maximum number of SPOC devices daisy-chained in each group supported by the driver.

1..2

(Higher values than 2 requires changes in the TSpocChannelDef)

SPOC_GROUP_CHANNELS

Maximum number of total PWM channels in each group. If there is more than one device per group, this parameter defines the sum of available channels.

1..n

For example, if we have two BTS5560GX daisy-chained, the value is 10.

SPOC_BUFFER_LENGTH Defines the resolution of PWM signal. Typically: 200.

For a 400 Hz PWM (T = 2.5ms), this gives tres = 12.5us 0.5% resolution

SPOC_ADC_TRIGGER_COUNT

Period of ADC trigger in FrameIndex

Higher ADC trigger period will limit the possibility to diagnose current of signal with small duty cycle.

2

SPOC_TX_FIFO_LEVEL Level of TX FIFO when the interrupt request will be generated.

This value has to be tuned according to the application. If TX FIFO buffer


SPOC PWM Driver API


length is 64, 50 is a ‘good’ value.

Two other parameters, SPOC_DUTY_MAX and SPOC_ADC_BUFFER_LENGTH, are calculated in the Spoc.h as follows: #define SPOC_DUTY_MAX (SPOC_BUFFER_LENGTH)

#define SPOC_ADC_BUFFER_LENGTH (SPOC_BUFFER_LENGTH / SPOC_ADC_TRIGGER_COUNT)

6.9.1 TSpocConfig structure

In addition to pre-compile configuration, there is TSpocConfig structure which defines the values to be passed through a pointer into the Spoc_Init() function.

6.10 Type definitions

The API imports some standard types previously defined in the file dependencies. • integer types, e.g. uint8, uint16, from StdTypes.h • boolean type and constants, from StdTypes.h • return type (TStdReturn) and constant, from StdTypes.h • usic_t, from registers_usic.h • TUsicIoSet, from port_io.h • TSscSlaveSelectOutput, from Ssc.h

In addition, SPOC driver defines its own types:

Identifier-type definitions: • TSpocGroup • TSpocChannel • TSpocPeriod

Configuration data type definitions: • TSpocChannelDef • TSpocDelayData • TSpocGroupConfig • TSpocConfig

Run-time data type definitions: • TSpocCommandBuffer • TSpocDiagnosticData • TSpocChannelData • TSpocGroupData • TSpocGroupDuty

6.10.1 TSpocGroup Type: Enumeration

Range: SPOC_GROUP_0 As reference for SPOC group 0 SPOC_GROUP_1 As reference for SPOC group 1 ... SPOC_GROUP_N As reference for SPOC group (SPOC_MAX_GROUPS-1)

Description: These constants are used as reference for specific SPOC group.


SPOC PWM Driver API


6.10.2 TSpocChannel Type: uint8 or Enumeration

Range: 0..(SPOC_GROUP_CHANNELS-1)

Description: These constants are used as reference for a SPOC channel.

6.10.3 TSpocPeriod Type: uint8 or Enumeration

Range: 0..(SPOC_NUM_SUPPORTED_PERIODS-1)

Description: These constants are used as reference for a SPOC PWM period.

6.10.4 TSpocChannelDef

Type: struct

Elements: uint16 Mask Mask for bit position of in the SPI command to control the output of a channel in a SPOC device.

This position is device-specific. uint16 Offset Offset (=Phase) of PWM signal with respect to the beginning of

SPI command buffer. uint16 AdcMuxCmd Command to select ISense output of this channel

This position is device-specific. uint16 AdcOffset Base offset in the SpocAdcResults buffer where the earliest

ADC result for this channel can be found. Description: Values in this structure are used for:

• calculating the pattern of SPI commands for a SPOC channel. • inserting ADC multiplexer command into correct command slot calculated based on

TSpocChannelDef.AdcOffset plus the TSpocDelayData.AdcOffsetB based on active group period.

6.10.5 TSpocDelayData Type: struct

Elements: bool Usable marker whether this delay information will be used or not uint8 DCTQ1 DCTQ1 parameter of usic’s SSC uint8 PCTQ1 PCTQ1 parameter of usic’s SSC uint16 AdcOffsetB Additional offset to retrieve ADC command from the duty-on

frame. Description: Values in this structure are used for:

• calculating the interframe delay of SPI commands for a SPOC group • calculating the total offset of the ADC result


SPOC PWM Driver API


Note: Actual elements are hardware-dependent. Above elements might be only specific to microcontroller with USIC peripheral, e.g. XC2000 Family.

6.10.6 TSpocGroupConfig Type: struct

Elements: usic_t* usic base address of the SPI hardware peripheral registers, i.e. USIC in XC2000

TUsicIoSet UsicIoSet identifier to a pair of SPI IO to use TSscSlaveSelectOutput SlaveSelectOutput

identifier to SPI slave select to use

TSpocPeriod InitialPeriod initial running period for the group uint8 NumDevices number of devices in daisy-chain of this group uint8 ChannelCount total number of channels of all devices in this group const TSpocDelayData* DelayData

pointer to the first element in the Delay table

const TSpocChannelDef* ChannelDefs

pointer to the first element in the Channel definition table

Description: Values in this structure are used to initialize data and to configure hardware needed by a SPOC group.

6.10.7 TSpocConfig Type: struct

Elements: uint8 GroupCount number of groups to configure const TSpocGroupConfig* FirstGroup

pointer to first element in group configuration table. Group index starts with SPOC_GROUP_0, i.e. value ‘0’

Description: Values in this structure are used to initialize overall driver hardware and data. Used by Spoc_Init()

6.10.8 TSpocCommandBuffer Type: struct

Elements: uint16 Buffer0[SPOC_BUFFER_LENGTH+1]

first SPI commands buffer

uint16 Buffer1[SPOC_BUFFER_LENGTH+1]

second SPI commands buffer

volatile uint8 Status bitwise status of the buffer, e.g:

SPOC_NDAT (0x80), bitmask indicating a new pattern is available in the other buffer

SPOC_USE (0x01), bitmask indicating current buffer in use by SPI, i.e. ‘0’ first buffer, ‘1’ second buffer.

uint16* CommandPtr pointer to the actual position of command to read,


SPOC PWM Driver API


used and update by SPI TX interrupt uint16* EndOfBuffer pointer to mark the limit position of the buffer, so

CommandPtr will not read from beyond dedicated buffer, used and updated by SPI TX interrupt

Description: This is dual-buffer strategy for calculating pattern of SPI command. When one buffer is used for transmission, the calculation will work on the other buffer. NDAT bit is stored in the Status variable.

This structure is element of TSpocGroupData

6.10.9 TSpocDiagnosticData Type: struct

Elements: uint16 Data[SPOC_BUFFER_LENGTH]

storage of diagnostic data read from SPI

uint16* DataPtr actual reading position of RX interrupt. However, since PEC or DMA is used, this element is not used.

Description: Definition of data structure for storage of SPI diagnostic, element of TSpocGroupData

6.10.10 TSpocChannelData Type: struct

Elements: uint16 Duty actual running duty of this channel.

Duty cycle in % = Duty / SPOC_BUFFER_LENGTH x 100 uint8 PeriodDivider

prescaler of the channel period, used to create pattern for more than one PWM in the RAM. E.g. if value is 0, one PWM pattern in the RAM will be generated. 1 = two PWM patterns. 2 = four PWM patterns, 3 = eight PWM patterns, and so on, factor of 2.

uint16* ADC_Value

pointer to the channel's ADC result in SpocAdcResults

Description: Definition of runtime channel data, element of TSpocGroupData

6.10.11 TSpocGroupData Type: struct

Elements: usic_t* usic base address to SPI peripheral register, given by configuration

TSpocGroup Number group number (for debugging purpose) TSpocCommandBuffer BufferSet SPI command buffer runtime data TSpocPeriod Period actual running period const TSpocDelayData* DelayData

pointer to the first element in the delay table, given by configuration

const TSpocChannelDef* ChannelDefs

pointer to the first element in the channel definition table, given by configuration

TSpocChannelData Channels[SPOC_GROUP_CHANNELS]

channel runtime data


SPOC PWM Driver API


TSpocDiagnosticData Diagnostic

group diagnostic data

Description: Definition of runtime group data

6.10.12 TSpocGroupDuty Type: struct

Elements: uint8 PeriodDivider[SPOC_GROUP_CHANNELS]

period divider for all channels in the group

uint16 ChannelDuty[SPOC_GROUP_CHANNELS]

on time of all channels in the group

Description: This structure contains information of all channels for calculation of SPI command patterns by Spoc_SetDutyCycleAll() function.

6.11 Exported Variables

6.11.1 SpocGroupCount Declaration: extern uint8 SpocGroupCount;

Description: Number of groups in use, zero if not initialized.

6.11.2 SpocGroups Declaration: extern TSpocGroupData SpocGroups[SPOC_MAX_GROUPS];

Description: Run-time group data

6.12 Public function prototypes

6.12.1 Spoc_Init Syntax: void Spoc_Init(const TSpocConfig* ConfigPtr)

Sync/Async: Synchronous

Re-entrancy: non re-entrant

Parameters(in): ConfigPtr Address to configuration structure that contains all information for operating this SPOC driver.

Parameters(out): none -- Return value: none -- Description:

This function: • initializes run-time driver and group variables • initializes also all SPI modules (usic channel) which are used by all SPOC groups.

Thus, the usic channels used here shall not be initialized/used for other purpose! • initializes ADC and triggering modules • initializes all IO ports used by SPI communication and ADC. • copies all needed information from the configuration data • is called within an UNLOCKED system registers state


SPOC PWM Driver API


ONLY after calling this function, other SPOC driver functions can be called (changed driver state to READY (Initialized)

6.12.2 Spoc_SetDutyCycle Syntax: TStdReturn Spoc_SetDutyCycle(TSpocGroup GroupNr, TSpocChannel ChannelNr,

uint16 Duty);



Parameters(in): GroupNr group number, 0..(SPOC_MAX_GROUPS-1) ChannelNr channel number in the group, 0..(ChannelCount-1) Duty channel on time, 0..SPOC_BUFFER_LENGTH


This function: • calculates new SPI command pattern, especially for the specific channel • inserts ADC mux command at the end of calculation • sets NDAT bit in the Status of TSpocCommandBuffer Resulting duty cycle is:

Duty cycle = (Duty * PeriodDivider / SPOC_BUFFER_LENGTH) * 100% Example: Duty = 0 0% duty cycle Duty = SPOC_BUFFER_LENGTH 100% duty cycle

6.12.3 Spoc_SetDutyCycleAll Syntax: TStdReturn Spoc_SetDutyCycle(TSpocGroup GroupNr, TSpocGroupDuty*

DutyPtr);



Parameters(in): GroupNr group number, 0..(SPOC_MAX_GROUPS-1) DutyPtr pointer to TSpocGroupDuty


This function: • calculates new SPI command pattern for all channels • inserts ADC mux command at the end of calculation • sets NDAT bit in the Status of TSpocCommandBuffer


SPOC PWM Driver API


6.12.4 Spoc_SetGroupPeriod Syntax: TStdReturn Spoc_SetGroupPeriod(TSpocGroup GroupNr, TSpocPeriod Period);



Parameters(in): GroupNr group number, 0..(SPOC_MAX_GROUPS-1) Period identifier to the expected period, see TSpocPeriod

Parameters(out): none -- Return value: E_OK when group period can be set succesfully

E_INVALID_PARAM when one of the parameter is not valid Description:

This function sets the group period, i.e. running frequency, of a SPOC group. This function takes effect only if the SPOC is not busy (query by Spoc_IsBusy() function). The group frequency can be changed using the DCTQ1 and PCTQ1 information in the TSpocDelayData.

6.12.5 Spoc_IsBusy Syntax: bool Spoc_IsBusy(TSpocGroup GroupNr)



Parameters(in): GroupNr group number, 0..(SPOC_MAX_GROUPS-1) Parameters(out): none -- Return value: TRUE the SPOC group is busy, e.g. due to SPI command buffer has

been modified but has not been taken by the TX interrupt service routine

FALSE the SPOC group is ready to receive new duty cycle or frequency setting.

Description: This function retrieves the status of the SPI buffer and communication, whether it is ready to receive duty-cycle or period modification. Due to availability of exported SpocGroups variable, this function can be made as inline.

6.12.6 Spoc_GetAdcValue Syntax: uint16 Spoc_GetAdcValue(TSpocGroup GroupNr, TSpocChannel ChannelNr)



Parameters(in): GroupNr group number, 0..(SPOC_MAX_GROUPS-1)


SPOC PWM Driver API


ChannelNr channel number in the group, 0..(SPOC_GROUP_CHANNELS-1) Parameters(out): none -- Return value: uint16 Value of channel’s ISense read by ADC hardware. Description:

This function retrieves the latest read value of ISense output of a specific SPOC channel in a group. Due to availability of exported SpocGroups variable, this function can be made as inline.

6.13 Interrupt Service Routines

The driver implements the service routines for handling several requests: 1. Transmit interrupt of SPI communication 2. Receive interrupt of SPI communication 3. End of ADC conversion Those service routines are implementation specific and are called from hardware specific interrupt frames (vectors).


Implementation in XC2000 Microcontroller Family


7 Implementation in XC2000 Microcontroller Family

7.1 Unique hardware features

XC2000 Family is 16-bit microcontroller which has several unique hardware features which improves a lot the performance in par with a 32-bit microcontroller. Key features used in this application notes are:

USIC (Universal Serial Interface Channel) • Data-FIFO with 64 entries (16 bit) • Time triggered FIFO entry transmission • Huge frame delay possible • Using transmit slave select event for triggering AD conversions

Analog to Digital Converter • Very fast conversion: 1,5 µs @ 10 bit • High accuracy: 2 LSB @ 10 bit • Hardware conversion trigger from various sources • Data reduction mode • Alias mode

Capture-Compare Unit 6 • Two 16 bit timer with hardware connectivity to USIC and ADC • Trigger on compare and period match

PEC (DMA-like) transfer • Direct memory access between memories and registers

7.2 Hardware Resource Mapping

In XC2000 Microcontroller Family, we can assign above requirements to the following hardware resources, thus implements a near complete solution. Availability of SPI FIFO and DMA-like feature reduces the CPU load a lot.

HW Requirement Fulfillment TX, RX, and ADC Buffer

Internal RAM

TX interrupt Number of interrupts is reduced due to availability of SPI transmit FIFO. RX interrupt Handled by PEC (DMA-like feature).

CPU interruption only occurs once every end of receive buffer for updating PEC pointer and counter

ADC interrupt Handled by PEC. CPU interruption only occurs once every end of A/D results buffer for updating PEC pointer and counter

Fixed-time SPI trigger

Interframe delay parameter. Directly supported by USIC (serial controller interface in XC2000)

ADC trigger/counter Direct connection from CCU6 timer to trigger ADC. In some XC2000 devices such as XC2000M (M-Step device and above), there’s a




direct connection from USIC to trigger the CCU6. For example in the XC2287 device, an external connection from slave select signal to the CCU6 T13 timer is needed ( Figure 17). On the other hand, in the new XC2286M device, this connection is available internally. Thus some I/O pins can be spared ( Figure 18).

Figure 17 Resources usage in XC2287 microcontroller (Sample Project #1)




DiagnosisData

CommandPattern

Command #0

Command #1

Command #2

Command #3

Command #4

Command #n

Data #0

Data #1

Data #2

Data #3

Data #4

Data #n

0

1

m

ADC result

RBUF

TX-FIFO

SlaveSelectDelay

SerialCLK

ControlTBUF

SELOUTSCLKDOUTDIN

USIC

PECtransfer Tx FIFO ISR

CCU6

T12

T12PR

CMP

T12HR

SR3

ADC

AN input

ConvT12PM

PECtransfer

XC2286MRAM

Figure 18 Resources usage in XC2286M microcontroller (Sample Project #2)


Sample Project #1 with XC2286M EasyKit


8 Sample Project #1 with XC2286M EasyKit In this sample project, we will set-up a XC2286M based microcontroller system controlling two SPOC groups. We use also BTS5560GX and BTS5682E evaluation boards.

(See also Sample Project # 2 in Chapter 9)

8.1 Required Equipments • XC2000 Family Evaluation Board (EasyKit) with XC2286M microcontroller • One evaluation board with 2 x BTS5560GX and Load Interface Board, assigned as SPOC Group 0 • One evaluation board with 1 x BTS5682E, assigned as SPOC Group 1 • PC and Debugger, USB cables • Necessary connection cables • Necessary power supplies

8.2 Required PC Software • Tasking EDE for XC2000 family, e.g. Tasking C166-ST10 EDE Version 8.7r1 • Debugger software • Terminal software for RS232, e.g. HyperTerminal or TeraTerm Pro.

8.3 Pin Assignment Signal XC2286M (EasyKit) SPOC Group 0

(BTS5560GX Board) SPOC Group 1 (BTS5682E Board)

MRST_0 P0.0 (U1C0 DIN) MRST1 --

MTSR_0 P0.1 (U1C0 DOUT) MTSR0 --

SCLK_0 P0.2 (U1C0 SCLKOUT) SCLK0 --

CS_0 P1.2 (U1C0 SELOUT6) CSA --

MRST_1 P3.0 (U2C0 DIN) -- SO

MTSR_1 P3.1 (U2C0 DOUT) -- SI

SCLK_1 P3.2 (U2C0 SCLKOUT) -- SCLK

CS_1 P1.3 (U2C0 SELOUT4) -- CS

ISENSE_0 P5.0 IS1 --

ISENSE_1 P15.0 -- IS

AGND VAGND AGND AGND

Figure 19 illustrates the interboard wiring for this sample project. More detailed information can be obtained from documentation of each evaluation board.




Figure 19 Sample Project #1 Interboard Wiring

8.4 Project Files Additionally to the SPOC driver files mentioned in Figure 16, more files are built together in this sample project. Important modules dependencies are illustrated in Figure 20.




Figure 20 Core modules in the sample project

Note: Spoc driver initializes only USIC pins used for SPI communication.

8.5 SPOC Driver Configuration

For this sample project, following sections describe the assignment of the necessary values to configure the SPOC driver.

8.5.1 Pre-compile parameters Name Assigned value Remarks SPOC_MAX_GROUPS 2

SPOC_DEVICES_PER_GROUP 2

In group 2, there is only one device (BTS5682E). But since Group 0 has 2 devices, here we assign the maximum number.

SPOC_GROUP_CHANNELS 10

In group 2, there are only 6 channels (BTS5682E). But since Group 0 has 10 channels, here we assign the maximum number.

SPOC_BUFFER_LENGTH 200 SPOC_ADC_TRIGGER_COUNT 2 SPOC_TX_FIFO_LEVEL 50




8.5.2 TSpocConfig structure values

const TSpocGroupConfig SpocGroupConfigs[SPOC_MAX_GROUPS] =

{

// GROUP 0: two BTS5590GX

{(usic_t*)SPOC_0_USIC, // usic

SPOC_0_USIC_IO, // UsicIoSet

SPOC_0_SELECT_OUT, // SlaveSelectOutput

SPOC_PERIOD_5ms , // InitialPeriod

2, // NumDevices

10, // ChannelCount

&SpocDelayData_Dual[0], // DelayDataPtr

&SpocChannelDefs_BTS5590GX[0]}, // ChannelDefsPtr

// GROUP 1: one BTS5682E

{(usic_t*)SPOC_1_USIC, // usic

SPOC_1_USIC_IO, // UsicIoSet

SPOC_1_SELECT_OUT, // SlaveSelectOutput

SPOC_PERIOD_5ms , // InitialPeriod

1, // NumDevices

6, // ChannelCount

&SpocDelayData_Single[0] , // DelayDataPtr

&SpocChannelDefs_BTS5682E[0]}, // ChannelDefsPtr

};

const TSpocConfig SpocConfig =

{

sizeof(SpocGroupConfigs)/sizeof(TSpocGroupConfig), // GroupCount = 2

&SpocGroupConfigs[0] // GroupConfigPtr

};

In the implementation of TSpocChannelDef structure, we define the following strategy: • Offset (= PWM phase) of channel 0 is 0 (zero) and then incremented by 10 for the next channels. • Mask contains bit position in the OUT command to control the channel’s output of the device. • AdcMuxCmd contains value of DCR command and is set as such that if one device in daisy-chain

active, other device’s ISense output is in high impedance (tristate).. • The lowest byte of Mask and AdcMuxCmd contains value related to the first device in the daisy-chain.

The next byte of Mask and AdcMuxCmd contains value related to the second device in the daisy-chain. • AdcOffset is the base offset in the ADC result buffer which corresponds to the time AdcMuxCmd is

transmitted. If SPOC_ADC_TRIGGER_COUNT == 2, then AdcOffset shall be half of Offset.

const TSpocChannelDef SpocChannelDefs_BTS5682E[6] = {

/* Mask, Offset, AdcMuxCmd, AdcOffset */

{ 0x0001, 0, 0xF6F0, 0},

{ 0x0002, 10, 0xF6F1, 5},

{ 0x0004, 20, 0xF6F2, 10},

{ 0x0008, 30, 0xF6F3, 15},

{ 0x0010, 40, 0xF6F4, 20},

{ 0x0020, 50, 0xF6F5, 25},




};

const TSpocChannelDef SpocChannelDefs_BTS5590GX[10] = {

/* Mask, Offset, AdcMuxCmd, DiagCmd, AdcOffset */

// 1nd device in chain

{ 0x0001, 0, 0xF6F0, 0},

{ 0x0002, 10, 0xF6F1, 5},

{ 0x0004, 20, 0xF6F2, 10},

{ 0x0008, 30, 0xF6F3, 15},

{ 0x0010, 40, 0xF6F4, 20},

// 2nd device in chain

{ 0x0100, 50, 0xF0F6, 25},

{ 0x0200, 60, 0xF1F6, 30},

{ 0x0400, 70, 0xF2F6, 35},

{ 0x0800, 80, 0xF3F6, 40},

{ 0x1000, 90, 0xF4F6, 45},

};

8.6 Shell operation Upon successfull booting, LED at P10.0 shall blink periodically (every 1 second).

The serial terminal (115200 baudrate) shall print following message:

-------------------------

PWM over SPI Program Demo

-------------------------

EasyKit XC2286M

SW Version : 1.0

Board Code : 0.0.0.0 (F.T.B.V)

Shell>

The command description can be obtained by typing “help” and press ENTER. Shell>help

help: show available commands version: display program info boardset (typ) (board) (ver): set board information set duty (group) (channel) (duty): set duty cycle (max. 200) set freq (group) (freq): set frequency (100,200,300,400) kHz set all (on/off) (group): set all channels on/off in the group

To switch on all channels of SPOC group 0, type: Shell>set all on 0

The shell command will set all channels on with 50% duty cycle by calling Spoc_SetDutyCycleAll() using the following data (see PwmShell.c):




For SPOC group 0: TSpocGroupDuty AllOnDuty =

{

{ 1, 1, 2, 4, 5, 1, 1, 2, 4, 5}, // PeriodDivider

{100,100, 50, 25, 20,100,100, 50, 25, 20}, // ChannelDuty to 50%

};

For SPOC group 1: TSpocGroupDuty AllOnDuty_1 =

{

{ 1, 1, 2, 2, 4, 5}, // PeriodDivider

{100,100, 50, 50, 25, 20}, // ChannelDuty to 50%

};

To switch on one channel, e.g. SPOC channel 2, with 50% duty cycle (Duty = 100, because SPOC_BUFFER_LENGTH=200), in group 0 type: Shell>set duty 0 2 100


Sample Project #2 with XC2287 Power EasyKit


9 Sample Project #2 with XC2287 Power EasyKit In this sample project, we will set-up a XC2287 Power EasyKit based microcontroller system controlling two SPOC groups.

9.1 Required Equipments and Software

The required equipments and PC software are similar to those of Sample Project #1 with the exception that here we use a XC2287 Power EasyKit.

9.2 Pin Assignment Signal XC2287 Power EasyKit SPOC Group 0 (BTS5560GX Board) MRST_0 P0.0 (U1C0 DIN) MRST1

MTSR_0 P0.1 (U1C0 DOUT) MTSR0

SCLK_0 P0.2 (U1C0 SCLKOUT) SCLK0

CS_0 P1.1 (U1C0 SELOUT5)

P5.8 (CCU60), important for triggering ADC!!

CSA

ISENSE_0 P5.0 IS1

AGND VAGND AGND

Figure 21 illustrates setup of this sample project. All needed connections are available through the board connectors. More detailed information can be obtained from documentation of each evaluation board.

Figure 21 Sample Project #2, Power EasyKit, SPOC Eval Board + Load Interface.


XC2000 CPU Performance


10 XC2000 CPU Performance

10.1 TX-FIFO Interrupt

Among the three interrupts (TX-FIFO, RX, and ADC), the most exhausting one is TX-FIFO interrupt where CPU needs to transfer SPI command from Group’s CommandBuffer into USIC Transmit FIFO buffer.

Figure 22 shows the occurences of TX-FIFO interrupt. The average time between two interrupts (tFifoReq) will be equal to the PWM resolution (tres) multiplied by SPOC_TX_FILL_LEVEL. The time to fill the TX-FIFO (tFifoFill) is the time of the interrupt service routine.

Figure 22 PWM Signal and Interruption.

Measurement of tFifoFill in the sample project is done by probing port pin P10.2 by oscilloscope. In the Spoc_int.c, we add toggling of P10.2 at the beginning and the end of the service routine.

interrupt (SPOC_0_TX_SRN) void __ISR_Spoc_Tx0(void)

{

#ifdef SPOC_DEBUG

IO_Write_P10(2, IO_TOGGLE); // start of ISR

#endif

SPOC_FILL_FIFO(SPOC_GROUP_0);

#ifdef SPOC_DEBUG

IO_Write_P10(2, IO_TOGGLE); // end of ISR

#endif

}

CPU load for TX-FIFO interrupt for one SPOC group is the ratio between tFifoFill and tFifoReq.




With SPOC_TX_FILL_LEVEL = 50 and XC2000-CPU runs at 80 MHz the measured tFifoFill is around 35 µs. The following table shows increasing CPU load due to increasing running frequency (reducing PWM resolution time). SPOC_BUFFER_LENGTH is 200.

Group Frequency (F) or Group Period (T) tres = T / 200 tFifoReq tFifoFill

TX Load (per group)

CPU Interrupt Load Total1 (per group)

F=100 Hz T=10.0 ms 50.0 µs 2500 µs 35 µs 1.4% 1.415% F=200 Hz T=5.0 ms 25.0 µs 1250 µs 35 µs 2.8% 2.83% F=400 Hz T=2.5 ms 12.5 µs 625 µs 35 µs 5.6% 5.66%

10.2 SPI-RX and ADC Diagnostic Interrupts

Since both interrupts are handled by PEC, the CPU receives interruption only at the end of RAM buffer to update PEC pointers.

• Rx interrupt occurs every: SPOC_BUFFER_LENGTH x tres

• ADC interrupt occurs every: SPOC_ADC_BUFFER_LENGTH x tres

Both interrupts in the sample project add CPU-load around 1.5 µs within each group period. Depending on the running frequency, the value corresponds to additional 0.015%, 0.03%, and 0.06% CPU load for 100, 200, and 400 Hz per group respectively; see the last column of previous table.

10.3 API Functions Execution Time

In order to measure execution time of an API function, we insert debug code to disable/enable all interrupts and toggle pin at before and after of function call. The pulse length of the P10.5 is measured by oscilloscope.

bool ShellCall_SetAllOnOff(TShellCallData* CallData)

{

...

while(Spoc_IsBusy(Group)){} // wait driver ready

#ifdef SPOC_DEBUG

IntEnabled = InterruptsDisable();

IO_Write_P10(5, IO_TOGGLE); // measurement start

#endif

Spoc_SetDutyCycleAll(Group, ...); // API function call

#ifdef SPOC_DEBUG

IO_Write_P10(5, IO_TOGGLE); // measurement end

InterruptsEnable(IntEnabled);

...

#endif

...

}

1 Including Rx and ADC interrupts




API Function Execution Time

(CPU 80MHz)

% relative to 100 Hz group

frequency Remarks

Spoc_SetDutyCycle(...) 200 µs 2 % SPOC_BUFFER_LENGTH = 200

Spoc_SetDutyCycleAll(...) 1.25 ms 12.5 % SPOC_BUFFER_LENGTH = 200

Group Channels = 10 Spoc_SetGroupPeriod(...) 19.6 µs 0.2 % --

Please note that before calling Spoc_SetDutyCycle() or Spoc_SetDutyCycleAll() we need to wait until the driver is in READY state. To be on the safe side and to reduce CPU load, each duty cycle function should be called only once in each group period.


Brightness Control (use case)


11 Brightness Control (use case) An additional aspect which is discussed here, but not included in the sample project, is PWM control in the case of variation of battery voltage (VBATT). The PWM controller takes VRMS as reference to maintain constant brightness of the bulb or LED and sets the correct duty cycle for each channel by using the following relation:

2

2

BATT

RMS

VV

DC =

The VBATT is obtained by using one of the available ADC channel, e.g. ADC0 in XC2000 and triggered using another ADC request source periodically (timed e.g. by another CCU6). The conversion value is put into different ADC result register and generates an interrupt for controlling the DutyCycle.

The minimum control period is equal to the SPOC group period.

Figure 23 Brightness control with SPOC PWM

11.1 Lookup Table

To simplify the calculation, a lookup table might be preferred. The following table shows Duty values which shall be passed through Spoc_SetDutyCycleAll() for different PeriodDividers (PD) in order to maintain the same brightness as 50% duty cycle at 12V. This table can be put as constant or populated during initialization of the PWM controller.

Duty (GroupPeriod = 200) vb_index

(in lookup table)VBATT DC

PD=1 PD=2 PD=4

0 9.00 1.78 178 89 45




1 9.44 1.62 162 81 41 2 9.88 1.48 148 74 37 3 10.31 1.35 135 68 34 4 10.75 1.25 125 63 31 5 11.19 1.15 115 58 29 6 11.63 1.07 107 54 27 7 12.06 0.99 99 50 25 8 12.50 0.92 92 46 23 9 12.94 0.86 86 43 22 10 13.38 0.80 80 40 20 11 13.81 0.75 75 38 19 12 14.25 0.71 71 36 18 13 14.69 0.67 67 34 17 14 15.13 0.63 63 32 16 15 15.56 0.59 59 30 15

The following code shows an example of the lookup table for the control of 10 channels with SPOC_BUFFER_LENGTH=200. With group period 100Hz, PeriodDivider varies from 1 to 4 to correspond to the channel period 100Hz .. 400Hz. // the 4 upper bits of the 12-bit ADC result are significant

#define VBATT_RES_BITS (4)

#define VBATT_LEVELS_COUNT (16) // Power(2,VBATT_RES_BITS)

#define VBATT_CONV_FACTOR (12-VBATT_RES_BITS)

// channels duty data in a group

TSpocGroupDuty GroupDutyData =

{

{ 1, 1, 2, 4, 4, 1, 1, 2, 4, 4}, // PeriodDivider

{100,100, 50, 25, 25,100,100, 50, 25, 25}, // ChannelDuty to 50%

};

// table populated with Duty values equivalent with 50% duty at 12V

uint16 GroupDutyTable[SPOC_GROUP_CHANNELS][VBATT_LEVELS_COUNT];

{

{178,162,148,135,125,115,107,99,92,86,80,75,71,67,63,59,}, // ch 0

{178,162,148,135,125,115,107,99,92,86,80,75,71,67,63,59,}, // ch 1

{89, 81, 74, 68, 62, 58, 53, 49,46,43,40,38,35,33,31,30,}, // ch 2

{44, 40, 37, 34, 31, 29, 27, 25,23,22,20,19,18,17,16,15,}, // ch 3

{44, 40, 37, 34, 31, 29, 27, 25,23,22,20,19,18,17,16,15,}, // ch 4

{178,162,148,135,125,115,107,99,92,86,80,75,71,67,63,59,}, // ch 5

{178,162,148,135,125,115,107,99,92,86,80,75,71,67,63,59,}, // ch 6

{89, 81, 74, 68, 62, 58, 53, 49,46,43,40,38,35,33,31,30,}, // ch 7

{44, 40, 37, 34, 31, 29, 27, 25,23,22,20,19,18,17,16,15,}, // ch 8

{44, 40, 37, 34, 31, 29, 27, 25,23,22,20,19,18,17,16,15,}, // ch 9

};




11.2 Control Routine

On the VBATT acquisition event, PWM CTR interrupt occurs. The service routine of this interrupt reads the value from assigned ADC result register (ADC_RESRx) and calculates new Duty for all channels.

In order to generate a unique interrupt, one dedicated ADC result register shall be selected too.

interrupt (ADC0_2_SRN) void BrightnessControl(void)

{

uint16 ChNr, Round, VBattIndex;

// obtained from ADC Result Register

uint16 AdcResult = (ADC0_RESR6 >> 2) & 0x3FF;

// see if rounding is needed by checking the bit next to the MSB

Round = (AdcResult & (0x1<<(VBATT_CONV_FACTOR-1))) >> (VBATT_CONV_FACTOR-1);

// calculate VBattIndex

VBattIndex = (AdcResult >> VBATT_CONV_FACTOR) + Round;

// look-up channel's Duty

for (ChNr=0;ChNr<SPOC_GROUP_CHANNELS;ChNr++)

{

GroupDutyData.ChannelDuty[ChNr] = GroupDutyTable[ChNr][VBattIndex];

}

// update channel's Duty

Spoc_SetDutyCycleAll(SPOC_GROUP_0, &GroupDutyData);

}

11.3 CPU Load

Following table shows the estimation of the execution time of such a PWM controller if we have one SPOC group with 10 channels and SPOC_BUFFER_LENGTH = 200.

Process (per group) Steps Time % Relative to 100 Hz group period

PWM CTR Interrupt + Lookup the DutyCycle for all channels based on acquired VBATT from ADC

5 µs 0.05%Brightness Control (one update per group period)

Update of SPI TX command buffer, e.g. call to Spoc_SetDutyCycleAll()

1.25 ms 12.5%

SPOC Driver TX-FIFO, ADC, RX Interrupts 1.415%

TOTAL 13.965%

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