Exercises 19.3 Programming Exercise
Write an assembly language program that blinks an LED five time. The LED will be on for 1 second then off for 1 second. Use the
sleep function for timing, which is described in
man 3 sleep.
@ blinkLED.s @ Blinks LED connected between pins 1 and 11 on Raspberry Pi @ GPIO connector once a second for five seconds. @ 2017-09-30: Bob Plantz @ Define my Raspberry Pi .cpu cortex-a53 .fpu neon-fp-armv8 .syntax unified @ modern syntax @ Constants for assembler .equ PERIPH,0x3f000000 @ RPi 2 & 3 peripherals @ .equ PERIPH,0x20000000 @ RPi zero & 1 peripherals .equ GPIO_OFFSET,0x200000 @ start of GPIO device @ The following are defined in /usr/include/asm-generic/fcntl.h: @ Note that the values are specified in octal. .equ O_RDWR,00000002 @ open for read/write .equ O_DSYNC,00010000 .equ __O_SYNC,04000000 .equ O_SYNC,__O_SYNC|O_DSYNC @ The following are defined in /usr/include/asm-generic/mman-common.h: .equ PROT_READ,0x1 @ page can be read .equ PROT_WRITE,0x2 @ page can be written .equ MAP_SHARED,0x01 @ share changes @ The following are defined by me: .equ O_FLAGS,O_RDWR|O_SYNC @ open file flags .equ PROT_RDWR,PROT_READ|PROT_WRITE .equ NO_PREF,0 .equ PAGE_SIZE,4096 @ Raspbian memory page .equ INPUT,0 @ use pin for input .equ OUTPUT,1 @ use pin for ouput .equ ONE_SEC,1 @ sleep one second .equ PIN17,17 @ pin set bit .equ FILE_DESCRP_ARG,0 @ file descriptor .equ DEVICE_ARG,4 @ device address .equ STACK_ARGS,8 @ includes sp 8-byte align @ Constant program data .section .rodata .align 2 device: .asciz "/dev/gpiomem" devErr: .asciz "Cannot open /dev/gpiomem\n" memErr: .asciz "Cannot map /dev/gpiomem\n" @ The program .text .align 2 .global main .type main, %function main: sub sp, sp, 24 @ space for saving regs @ (keeping 8-byte sp align) str r4, [sp, 4] @ save r4 str r5, [sp, 8] @ r5 str r6, [sp,12] @ r6 str fp, [sp, 16] @ fp str lr, [sp, 20] @ lr add fp, sp, 20 @ set our frame pointer sub sp, sp, STACK_ARGS @ Open /dev/gpiomem for read/write and syncing ldr r0, deviceAddr @ address of /dev/gpiomem ldr r1, openMode @ flags for accessing device bl open cmp r0, -1 @ check for error bne gpiomemOK @ no error, continue ldr r0, devErrAddr @ error, tell user bl printf b allDone @ and end program gpiomemOK: mov r4, r0 @ use r4 for file descriptor @ Map the GPIO registers to a main memory location so we can access them str r4, [sp, FILE_DESCRP_ARG] @ /dev/gpiomem file descriptor ldr r0, gpio @ address of GPIO str r0, [sp, DEVICE_ARG] @ location of GPIO mov r0, NO_PREF @ let kernel pick memory mov r1, PAGE_SIZE @ get 1 page of memory mov r2, PROT_RDWR @ read/write this memory mov r3, MAP_SHARED @ share with other processes bl mmap cmp r0, -1 @ check for error bne mmapOK @ no error, continue ldr r0, memErrAddr @ error, tell user bl printf b closeDev @ and close /dev/gpiomem @ All OK, blink the LED mmapOK: mov r5, r0 @ use r5 for programming memory address mov r0, r5 @ programming memory mov r1, PIN17 @ pin to blink mov r2, OUTPUT @ it's an output bl gpioPinFSelect @ select function mov r6, 5 @ blink five times loop: mov r0, r5 @ GPIO programming memory mov r1, PIN17 bl gpioPinClr mov r0, ONE_SEC @ wait a second bl sleep mov r0, r5 mov r1, PIN17 bl gpioPinSet mov r0, ONE_SEC @ wait a second bl sleep subs r6, r6, 1 @ decrement counter bgt loop @ loop until 0 mov r0, r5 @ memory to unmap mov r1, PAGE_SIZE @ amount we mapped bl munmap @ unmap it closeDev: mov r0, r4 @ /dev/gpiomem file descriptor bl close @ close the file allDone: mov r0, 0 @ return 0; add sp, sp, STACK_ARGS @ fix sp ldr r4, [sp, 4] @ restore r4 ldr r5, [sp, 8] @ r5 ldr r6, [sp,12] @ r6 ldr fp, [sp, 16] @ fp ldr lr, [sp, 20] @ lr add sp, sp, 24 @ sp bx lr @ return .align 2 @ addresses of messages deviceAddr: .word device openMode: .word O_FLAGS gpio: .word PERIPH+GPIO_OFFSET devErrAddr: .word devErr memErrAddr: .word memErr
@ gpioPinClr.s @ Clears a GPIO pin. Assumes that GPIO registers @ have been mapped to programming memory. @ Calling sequence: @ r0 <- address of GPIO in mapped memory @ r1 <- pin number @ bl gpioPinClr @ 2017-09-30: Bob Plantz @ Define my Raspberry Pi .cpu cortex-a53 .fpu neon-fp-armv8 .syntax unified @ modern syntax @ Constants for assembler .equ PIN,1 @ 1 bit for pin .equ PINS_IN_REG,32 .equ GPCLR0,0x28 @ clear register offset @ The program .text .align 2 .global gpioPinClr .type gpioPinClr, %function gpioPinClr: sub sp, sp, 16 @ space for saving regs str r4, [sp, 0] @ save r4 str r5, [sp, 4] @ r5 str fp, [sp, 8] @ fp str lr, [sp, 12] @ lr add fp, sp, 12 @ set our frame pointer add r4, r0, GPCLR0 @ pointer to GPSET regs. mov r5, r1 @ save pin number @ Compute address of GPSET register and pin field mov r3, PINS_IN_REG @ divisor udiv r0, r5, r3 @ GPSET number mul r1, r0, r3 @ compute remainder sub r1, r5, r1 @ for relative pin position lsl r0, r0, 2 @ 4 bytes in a register add r0, r0, r4 @ address of GPSETn @ Set up the GPIO pin funtion register in programming memory ldr r2, [r0] @ get entire register mov r3, PIN @ one pin lsl r3, r3, r1 @ shift to pin position orr r2, r2, r3 @ clear bit str r2, [r0] @ update register mov r0, 0 @ return 0; ldr r4, [sp, 0] @ restore r4 ldr r5, [sp, 4] @ r5 ldr fp, [sp, 8] @ fp ldr lr, [sp, 12] @ lr add sp, sp, 16 @ restore sp bx lr @ return