SMSC LAN8700 Datasheetww1.microchip.com/downloads/cn/AppNotes/cn572347.pdfThe modified resume behavior is designed for use in systems that may power down the host under sus-pended

AN 1826Implementing the Suspend Indicator Using Microchip

USB Hubs

INTRODUCTIONThe USB251xB / USB3x03 / USB253x / USB3x13 / USB46x6 product lines are a family of feature-rich, low power USB 2.0 hubs optimized for use in embedded systems where high performance and advanced functionality are critical design requirements. The USB251xB / USB3x03 / USB253x / USB3x13 / USB46x6 product lines feature a suspend indicator which can be used to signal to an embedded controller the suspend status of the hub. This feature is useful for signaling when a system should enter or exit a low power state.

AUDIENCEThis application note is targeted towards hardware/software/firmware engineers looking for detailed information on how to implement the suspend indicator feature on Microchip USB hubs in order to facilitate low power operation of their USB designs.

REFERENCESThe following documents should be referenced when using this application note. See your Microchip representative for availability.

• USB251xB Datasheet• USB2532 Datasheet• USB2533 Datasheet• USB2534 Datasheet• USB3503 Datasheet• USB3803 Datasheet• USB3613 Datasheet• USB3813 Datasheet• USB4604 Datasheet• USB4624 Datasheet

Author: Andrew Rogers Microchip Technology

2014 Microchip Technology Inc. DS00001826A-page 1

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1.0 USB SUSPENDThe ability to place a device into a low power state is an important feature for designs that are battery powered or are otherwise sensitive to total power consumption. Therefore, the ability to place a device into a suspended, low power state is crucial. While in the suspended state, a device may draw no more than 0.5 mA from VBUS. While in suspend, the device must still monitor DP and DM for the RESUME signal (Data K), or the RESET signal (SE0 for over 2.5μs).
Under normal operation, a Start-of-Frame (SOF) packet is sent by the host every 1 ms. This signal keeps to device awake. When the host wants to place a device into the suspended state, it will simple drive a static SUSPEND (Data J) signal and not send any packets to the device for 3 ms.

Any USB Reset signal or HSIC Reset signal will clear the remote wake up feature.

1.1 Methods of Resuming USB Operation

1.1.1 HOST DRIVEN RESUMEAfter a hub or device has been placed in suspend, a host may force a hub or a device to resume normal operation at any time. This is achieve by driving the RESUME signal (Data K) on the data lines for a minimum of 20 ms followed by an End-of-Packet signal (EOP).

1.1.2 REMOTE WAKEUPIf a device or hub has its remote wakeup feature enabled it may trigger the resume. The device will send the RESUME signal on the data lines in order to wake up the host for at least 1 ms.The host must recognize the RESUME signal and take over driving the remainder of the resume signal.

A hub will only propagate the RESUME signal from a downstream device to the upstream port if it has been configured by the host to enable “remote wakeup”. A HID (Human Interface Device) is a common example of a device that may attempt to wakeup the host when there is some sort of input activity, such as mouse movement.

A specific USB command must be sent to the hub in order to enable “remote wakeup”. A host must send the SET_FEA-TURE with wValue = DEVICE_REMOTE_WAKEUP device request to the hub after enumeration. See section 9.4 of the USB2.0 specification for additional details.

DS00001826A-page 2 2014 Microchip Technology Inc.

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2.0 SUSPEND INDICATOR OVERVIEW
2.1 Use Cases

2.1.1 REMOTE WAKEUP INDICATIONIf the hub has been configured to allow for remote wakeup, the suspend indicator functionality can be used to indicate when a downstream device has been inserted into the port or an already connected downstream device is attempting to wake up the host.

2.1.2 SOC SUSPEND INDICATIONIf there is an embedded SOC within the system that is does not have USB connectivity, the hub can be used to com-municate when it has been placed into suspend by the host and when it has resumed operation.

2.2 Microchip Hub Suspend Indicator Modes

2.2.1 NORMAL RESUME BEHAVIORThe suspend indicator pin operating under normal resume behavior is static in nature. The suspend indicator pin will assert when the hub is active, and deassert when the hub is suspended.

Under normal operation, the hub will also drive a RESUME signal on the data lines when attempting to exit the sus-pended state.

2.2.2 MODIFIED RESUME BEHAVIORSeveral Microchip hubs have an alternate suspend indicator mode. When operating under this mode, the suspend indi-cator pin will generate a pulse when it is attempting to resume operation. The host must react to the suspend indicator pulse by driving the RESUME signal.

Under modified operation, the hub will not drive a RESUME signal on the data lines when attempting to exit the sus-pended state. The modified resume behavior is designed for use in systems that may power down the host under sus-pended operation; in such a case the driving of a RESUME signal is undesirable due to back-drive concerns. See Table 1 for information on which Microchip hubs have this feature.


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3.0 SUSPEND INDICATOR DEFAULTS AND BEHAVIOR BY PARTThe suspend indicator pin properties and default configuration settings differ from part to part. Not all hubs can operate under the Modified Suspend behavior. Jump to Chapter 4 for the details regarding how to configure the suspend indi-cator settings. See Table 1 for part specific information.
3.1 USB2512B, USB2513B, and USB2514BDuring normal operation, the SUSP_IND pin provides an indication of the active or suspended state of the hub; the SUS-P_IND pin will drive HIGH when the hub is active, and drive LOW when suspended. If the enable remote wakeup feature has been set by the host, the hub will drive a ‘Data K’ on the upstream port to signal to the host that it is ready to connect.

The suspend indicator feature is enabled by default on the USB2512B, USB2513B, and USB2514B. The USB2512B, USB2513B, and USB2514B devices do not have a Modified Suspend Behavior feature.

FIGURE 3-1: USB2514B ENTERING SUSPEND UNDER NORMAL RESUME OPERATION

TABLE 1: SUSPEND INDICATOR ATTRIBUTES BY PART NUMBER

Part Number SUSP_IND Pin Type Modified Suspend Behavior? Default Configuration

USB2512B Active Low No EnabledUSB2513B Active Low No EnabledUSB2514B Active Low No EnabledUSB3503 Open Drain No DisabledUSB3803 Open Drain No DisabledUSB2532 Active High Yes DisabledUSB2533 Active High Yes DisabledUSB2534 Active High Yes DisabledUSB3613 Active High Yes DisabledUSB3813 Active High Yes DisabledUSB4604 Active High No DisabledUSB4624 Active High No Disabled


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FIGURE 3-2: USB2514B RESUME UNDER NORMAL RESUME OPERATION
3.2 USB3503 and USB3803During normal operation, the SUSP_IND pin provides an indication of the active or suspended state of the hub; the SUS-P_IND pin on the USB3503 and USB3803 is open drain will float HIGH to the pull up voltage when the hub is active, and pull LOW when suspended. If the enable remote wakeup feature has been set by the host, the hub will drive a ‘Data K’ on the upstream port to signal to the host that it is ready to connect.

The suspend indicator feature is disabled by default on the USB3503 and USB3803. The USB3503 and USB3803 devices do not have a Modified Suspend Behavior feature.

To enable the Normal Resume Behavior on USB3503 or USB3803 during the hub configuration stage:

To disable the Normal Resume Behavior on USB3503 or USB3803during the hub configuration stage:

SMBus_Write(ADDR=0x8, REGISTER= 0xEE, VALUE=0x50)

SMBus_Write(ADDR=0x8, REGISTER= 0xEE, VALUE=0x10)


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FIGURE 3-3: USB3803 ENTERING SUSPEND UNDER NORMAL RESUME OPERATION
FIGURE 3-4: USB3803 RESUME UNDER NORMAL RESUME OPERATION

3.3 USB2532, USB2533, and USB2534

3.3.1 NORMAL RESUME BEHAVIORUnder Normal Resume Behavior the hub will monitor HUB_CONNECT to detect presence of the Host. If HUB_CON-NECT = ‘1’, then D+ pull-up is asserted and normal USB functionality is enabled. If VBUS_DET = ‘0’, then the D+ pull-up is negated. If battery charging is not enabled, the internal hub logic will be reset, thus negating all downstream ports and associated downstream VBUS enable signals. The hub will need to be re-enumerated to function, much like a new connection or after a complete system reset.


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During normal operation, the SUSP_IND pin provides an indication of the active or suspended state of the hub; the SUS-P_IND pin will drive LOW when the hub is active, and drive HIGH when suspended. If the enable remote wakeup feature has been set by the host, the hub will drive a ‘Data K’ on the upstream port to signal to the host that it is ready to connect.
To enable the Normal Resume Behavior on USB2532,USB2533, or USB2534 during the hub configuration stage:

,

To disable the Normal Resume Behavior on USB2532,USB2533, or USB2534 during the hub configuration stage:


SMBus_Write(ADDR=0x2C, REGISTER= 0x3C51, VALUE=0x40)

SMBus_Write(ADDR=0x2C, REGISTER= 0x3C51, VALUE=0x00)


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3.3.2 MODIFIED RESUME BEHAVIORWhen operating under Modified Resume Behavior the SUSP_IND pin serves as a “wakeup” signal. The SUSP_IND pin will pulse high only when activity from a downstream device is attempting to remote wakeup the host.

Under Modified Resume Behavior, hub will not reset itself if HUB_CONNECT is driven low. The hub will not drive a ‘K’ on the upstream port when operating under the modified resume behavior. This behavior is useful for when the host connected to the hub is powered down and therefore not driving VBUS. In addition, a powered down host may be sus-ceptible to any back-drive which may occur from the ‘K’ on the upstream port.

The Modified Resume Behavior will only operate properly and generate a pulse if the following condition are met:

• Downstream battery charging is disabled. The Modified Resume Behavior is design for low power consumption applications.

• Remote Wakeup is enabled for the hub. A host must send the SET_FEATURE with wValue = DEVICE_RE-MOTE_WAKEUP device request to the hub after enumeration. See section 9.4 of the USB2.0 specification for additional details.

• The device has been placed into suspend by the host.• VBUS_DETECT is low.

To enable the Modified Resume Behavior on the USB2532, USB2533, or USB2534 during the hub configuration stage:

To disable the Modified Resume Behavior on the USB2532, USB2533, or USB2534 during the hub configuration stage:

SMBus_Write(ADDR=0x2C, REGISTER=0x3008, VALUE=0x18)



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FIGURE 3-7: USB2534 DEVICE REMOTE WAKEUP UNDER MODIFIED RESUME BEHAVIOR
3.4 USB3613 and USB3813

3.4.1 NORMAL RESUME BEHAVIORUnder Normal Resume Behavior the hub will monitor HUB_CONNECT to detect presence of the Host. If HUB_CON-NECT = ‘1’, then D+ pull-up is asserted and normal USB functionality is enabled. If VBUS_DET = ‘0’, then the D+ pull-up is negated. If battery charging is not enabled, the internal hub logic will be reset, thus negating all downstream ports and associated downstream VBUS enable signals. The hub will need to be re-enumerated to function, much like a new connection or after a complete system reset.


To enable the Normal Resume Behavior on USB 3613 or USB3813 during the hub configuration stage:

To disable the Normal Resume Behavior on USB3613 or USB3813 during the hub configuration stage:

SMBus_Write(ADDR=0x2C, REGISTER=0x3C51, VALUE=0x40)



AN 1826

3.4.2 MODIFIED RESUME BEHAVIORWhen operating under Modified Resume Behavior the SUSP_IND pin serves as a “wakeup” signal. The SUSP_IND pin will pulse high only when activity from a downstream device is attempting to remote wakeup the host.

Under Modified Resume Behavior, hub will not reset itself if HUB_CONNECT is driven low. The hub will not drive a ‘K’ on the upstream port when operating under the modified resume behavior. This behavior is useful for when the host connected to the hub is powered down and therefore not driving VBUS. In addition, a powered down host may be sus-ceptible to any back-drive which may occur from the ‘K’ on the upstream port.

The Modified Resume Behavior will only operate properly and generate a pulse if the following condition are met:


AN 1826
• Downstream battery charging is disabled. The Modified Resume Behavior is design for low power consumption
applications.• Remote Wakeup is enabled for the hub. A host must send the SET_FEATURE with wValue = DEVICE_RE-

MOTE_WAKEUP device request to the hub after enumeration. See section 9.4 of the USB2.0 specification for additional details.

• The device has been placed into suspend by the host.• HUB_CONNECT is low.

To enable the Modified Resume Behavior on the USB3613 or USB3813 during the hub configuration stage:

To disable the Modified Resume Behavior on the USB3613 or USB3813 during the hub configuration stage:

FIGURE 3-10: USB3813 DEVICE REMOTE WAKEUP UNDER MODIFIED RESUME BEHAVIOR

3.5 USB4604 and USB4624Under Normal Resume Behavior the hub will monitor VBUS_DET to detect presence of the Host. If VBUS_DET = ‘1’, then D+ pull-up is asserted and normal USB functionality is enabled. If VBUS_DET = ‘0’, then the D+ pull-up is negated. If battery charging is not enabled, the internal hub logic will be reset, thus negating all downstream ports and associated downstream VBUS enable signals. The hub will need to be re-enumerated to function, much like a new connection or after a complete system reset.





AN 1826

To enable the Normal Resume Behavior on the USB4604 or USB4624 during the hub configuration stage:

To disable the Normal Resume Behavior on the USB4604 or USB4624 during the hub configuration stage:





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3.5.1 MODIFIED RESUME BEHAVIORThe USB4604 and USB4624 do not have a Modified Resume Behavior feature.


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4.0 SUSPEND INDICATOR CONFIGURATION
4.1 OTP Write with ProTouch SoftwareThe suspend indicator configurations can be written into the hub’s internal OTP using ProTouch software. The hub loads the configuration data from the OTP at every power-on.

4.2 SMBus ConfigurationThe configuration data can be written to the registers during the SoC_CFG start-up stage of operation. This needs to be done every time the part is powered on, reset, or VBUS_DET is toggled.

After the configuration writes are complete, the host must send the “USB Attach” command to the hub to begin enumer-ation.

4.3 Modified Resume Behavior Wakeup Pulse Length RegisterFor the hubs that have the Modified Resume Behavior feature, the width of the wakeup pulse can be modified by writing to the registers shown in Table 2. The width can be modified to generate from 0ms up to 19ms; the default pulse width is 14ms.

TABLE 2: GLOBAL_RESUME_TIME REGISTER (REGISTER ADDRESSES: 0X3190~3193)BIT NAME R/W DESCRIPTION

31:22 Reserved R Always read ‘0’21:0 RESUME_TIME R/W Timing for global resume in 60MHz clock cycles. May

be programmed to a maximum of 19ms.


AN 1826
APPENDIX A: APPLICATION NOTE REVISION HISTORY
TABLE A-1: REVISION HISTORY

Revision Level & Date Section/Figure/Entry Correction

Note: AN 1826, Revision A replaces the previous SMSC version, Revision 1.0.



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AN 1826

Note the following details of the code protection feature on Microchip devices:• Microchip products meet the specification contained in their particular Microchip Data Sheet.

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SMSC LAN8700 Datasheetww1.microchip.com/downloads/cn/AppNotes/cn572347.pdfThe modified resume behavior is designed for use in systems that may power down the host under sus-pended