ARM Processor and Memory

Architecture

Goal: Turn on an LED

Assignment 1Knight Rider Display - Larson Scanner

Babbage Difference Engine

http://www.theguardian.com/technology/2015/apr/12/thrilling-adventures-ada-lovelace-charles-babbage-sydney-padua

Analytical Engine

Universal Computer

Broadcom 2865 ARM Processor

Samsung 4Gb (gigabit) SDRAM

Package on Package

Running a Program

Fetch Instruction

Decode Instruction

Execute InstructionClock

10000000016Memory used to storeboth instructionsand data

Storage locations areaccessed using 32-bit addresses

Maximum addressable memory is 4 GB (gigabyte)

Address refers to a byte (8-bits)

Memory Map

0000000016

10000000016

02000000016512 MB Actual Memory

Memory Map

ARM Architecture / Floor Plan

Key Fact: Everything is organized into 32-bit words

Registers

ALU

DATA

ADDR

INST

+

Memory

r15r14r13r12r11r10r9r8r7r6r5r4r3r2r1r0

ADDR

pc=r15

r15 holds the program counter (pc)

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

Instruction Fetch

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

INST = Memory[ADDR]

pc

pc=r15

Instruction Fetch

Addresses and instructions are 32-bit words

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

pc+4

r15=pc+4

pc

Calculate address of next instructionWhy pc+4?

Instruction Fetch

Arithmetic-Logic Unit (ALU)

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR r2

r1

r0

addr0,r1,r2

r0=r1+r2

ALU only operates on registersRegisters are also 32-bit words

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

1

r1

r0

addr0,r1,#1

Immediate Value (#1)stored in INST

Add Instruction

Meaning (defined as math or C code)

r0=r1+r2

Assembly language (result is leftmost register)

addr0,r1,r2

Machine code (more on this later)

E0810002

1Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

r0movr0,#1

Move Immediate (constant)

VisUAL

Conceptual Questions

1. Suppose your program starts at 0x8000, what assembly language instruction could you execute to jump to and start executing instructions at that location.

2. If all instructions are 32-bits, can you move any 32-bit constant value into a register using a single mov instruction?

3. What is the difference between a memory location and a register?

Load and Store Instructions

ldrr0,[r1]

r1

ADDR=r1DATA= Memory[ADDR]

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

Load from Memory to Register (LDR)

Step 1

r0r0=DATA

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

Step 2

Load from Memory to Register (LDR)

r0

strr0,[r1]

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

Store Register in Memory (STR)

DATA=r0Step 1

r1

Registers

ALU

DATA

ADDR

INST

+

Memory

ADDR

Store Register in Memory (STR)

ADDR=r1Memory[ADDR]=DATAStep 2

strr0,[r1]

Turning on an LED

General-Purpose Input/Output (GPIO) Pins

54 GPIO Pins

Computers have Peripherals that Interface to the World

GPIO Pins are Peripherals

1 -> 3.3V0 -> 0.0V (GND)

Connect LED to GPIO 20

3.3V

1k

GND

GPIO Pins are Peripherals

Peripherals are Controlled by Special Memory Locations

"Peripheral Registers"

02000000016

10000000016Memory Map 4 GB

Ref: BCM2835-ARM-Peripherals.pdf

Peripheral registers are mapped into address space

Memory-Mapped IO(MMIO)

MMIO space is abovephysical memory

512 MB

General-Purpose IO Function

3 bits required to select function

Bit pattern Pin Function000 The pin in an input 001 The pin is an output 100 The pin does alternate function 0 101 The pin does alternate function 1 110 The pin does alternate function 2111 The pin does alternate function 3011 The pin does alternate function 4010 The pin does alternate function 5

GPIO Pins can be configured to beINPUT, OUTPUT, or ALT0-5

2 1 05 4 38 7 69101114 13 1215161720 19 1821222326 25 242728293031

GPIO 0GPIO 1GPIO 3 GPIO 4GPIO 5GPIO 6 GPIO 7GPIO 8GPIO 9 GPIO 2

GPIO Function Select Register

8 functions requires 3 bits to specify

10 pins times 3 bits = 30 bits

32-bit register (2 wasted bits)

"Function" is INPUT, OUTPUT (or ALT0-5)

54 GPIOs pins requires 6 registers

Watchoutfor…Manualsays:0x7E200000Replace7Ewith20:0x20200000

Ref: BCM2835-ARM-Peripherals.pdf

GPIO Function Select Registers Addresses

//SetGPIO20tobeanoutput

//FSEL2=0x20200008movr0,#0x20//r0=#0x00000020lslr1,r0,#24//r1=#0x20000000lslr2,r0,#16//r2=#0x00200000orrr1,r1,r2//r1=#0x20200000orrr0,r1,#0x08//r0=#0x20200008

movr1,#1//1indicatesOUTPUTstrr1,[r0]//store1to0x20200008

Note this also makes GPIO 21-29 into inputs

2 1 05 4 38 7 69101114 13 1215161720 19 1821222326 25 242728293031

34 33 3237 36 3540 39 3841424346 45 4447484952 51 5053

2020001C:GPIOSET0Register20200020:GPIOSET1Register

GPIO Function SET Register

Notes1. 1 bit per GPIO pin2. 54 pins requires 2 registers

//SetGPIO20outputHigh(3.3V)//AssumesGPIO20configuredtobeoutput//FSET0=0x2020001cmovr0,#0x20//r0=0x00000020lslr1,r0,#24//r1=0x20000000lslr2,r0,#16//r2=0x00200000orrr1,r1,r2//r1=0x20200000orrr0,r1,#0x1c//r0=0x2020001c

movr1,#1//r1=0x00000001lslr1,r1,#20//r1=0x00100000strr1,[r0]//storer1to0x2020001c

//loopforeverloop:bloop

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#EjectandremoveSDcard

##InsertSDcardintoSDHCslotonpi##Applypowerusingusbconsolecable.#PowerLED(Red)shouldbeon.##Raspberrypiboots.ACTLED(Green)#flashes,andthenisturnedoff##LEDconnectedtoGPIO20turnson!!#

Assignment 0

- Join forum https://edstem.org/us/courses/21299

- Read and understand our guides on basic topics (electricity, numbers, unix). Practice unix command line

- Checkout the course directory from gitbub

- Checkout your assignment directory and answer the questionnaire, check-in to submit assignment

- Setup your development environment before lab

Key Concepts• Bits are bits; fundamental bitwise operations

• Memory addresses refer to bytes (8-bits), words are 4 bytes

• Memory stores both instructions and data

• Computers repeatedly fetch, decode, and execute instructions

• Different types of ARM instructions: ALU, Loads and Stores, Branches

• General purpose IO (GPIO), peripheral registers, and MMIO

Further Reading

If you want to learn more about high-level computer organization and instructions, Chapter 2 of Computer Organization and Design: The Hardware/Software Interface (Patterson and Hennessy) is an excellent place to start.

Or take EE180 next Winter!