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j3lda1
j3lda1
Associate
September 30, 2012
Question

STM32VL - example using interrupts in ASM

  • September 30, 2012
  • 5 replies
  • 2038 views
Posted on September 30, 2012 at 11:51

Hello, I am new in programming of STM32VL Discovery. I would like to write program in assembler for blinking LEDs using interrupts.

But it is so difficult to find examples in ASM and I can�t find some example in ASM with interrupts. Do you have some example where are used interrupts (handlers,..)?

Can you help me? Thanks a lot 

#books
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    5 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    October 1, 2012
    Posted on October 01, 2012 at 05:07

    Do you have any experience of ARM/Thumb assembler to draw from?

    In Keil, I might use the SysTick to periodically toggle LED3 thusly 

    SysTick_Handler PROC
EXPORT SysTick_Handler
ldr r0, =0x40011000 ; GPIOC
ldr r1, =0x200 ; Pin 9, LED3
ldr r2, [r0, #0xC] ; GPIOC->ODR
and r2, r2, r1 ; Mask bits to toggle
lsl r3, r2, #16 ; Get reset bits to high order
eor r2, r2, r1 ; Invert set in low order
orr r2, r2, r3 ; Combine
str r2, [r0, #0x10] ; GPIOC->BSRR
bx lr
ENDP

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    Andrew Neil
    Andrew Neil
    Super User
    October 1, 2012
    Posted on October 01, 2012 at 09:10

    Any particular reason why it has to be assembly, rather than, say, 'C' ?

    In Assembly, you are dealing directly with the Cortex-M3 instruction set - which is defined by ARM, and not specific to ST or the STM32.

    So the place to start would be the ARM technical reference site: http://infocentre.arm.com

    Get yourself a copy of  ''The Definitive Guide to the ARM Cortex-M3'' by Joseph Yiu 

    eg,

    http://www.amazon.co.uk/The-Definitive-Guide-ARM-Cortex-M3/dp/185617963X/ref=sr_1_1?ie=UTF8&qid=1349075537&sr=8-1

    More ARM Books here:

    http://www.keil.com/books/armbooks.asp

    In the ARM 'Community' section, you will find training providers, consultants, etc:

    http://www.arm.com/community/index.php

    A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
    j3lda1
    j3lda1Author
    Associate
    October 1, 2012
    Posted on October 01, 2012 at 11:05

    Thank you, LEDs are blinking now. I was trying to use TIM3 handler, but SYStick handler is definitely better (easier to write in ASM). I must write this in ASM because our teacher wants that. We can use ''delay'' function for blinking LEDs, but I want have better solution... 

    j3lda1
    j3lda1Author
    Associate
    October 1, 2012
    Posted on October 01, 2012 at 12:49

    Only one thing is for me still unclear.

    I used code from THE DEFINITIVE GUIDE TO THE ARM CORTEX-M3:

     LDR     R0, =0xE000E010 ; SYSTICK control and status register

     MOV     R1, #0          

     STR     R1, [R0]        ; stop counter to prevent interrupt triggered accidentally

     LDR     R1, =11999999   ; trigger every 12000000 cycles

     STR     R1, [R0,#4]     ; write reload value to reload value register

     STR     R1, [R0,#8]     ; write any value tu current value

     MOV     R1, #0x7        ; enable interrupt, enable SYSTICK counter

     STR     R1, [R0]        ; start counter

    Now, it´s blinking every 1 second (0,5s is shining and 0,5s isn´t shining). I thought that when I want blinking every 2 seconds, I only need set  LDR     R1, =23999999. But it´s blinking even faster! Do you know ,why?

    Tesla DeLorean
    Tesla DeLorean
    Guru
    October 1, 2012
    Posted on October 01, 2012 at 13:25

    Confirm what SYSCLK is, 8 MHz, 24 MHz

    Check if SysTick is at SYSCLK or SYSCLK/8

    The count is 24-bit, so largest value is 16777216.

    Larger values give slower speeds.

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