Re: arm-elf-gcc building erroneous code for ISR (long posting)

From: Peter Dickerson (first{dot}surname_at_ukonline.co.uk)
Date: 06/17/04 

Date: Thu, 17 Jun 2004 17:51:08 +0100

"Jens Hildebrandt" <jens.hildebrandt@remove_this.etechnik.uni-rostock.de>
wrote in message news:40cd60da@news.uni-rostock.de...
> Hello group,
>
> I'm curently trying to get familiar with the ARM7 by building some
> example-projects for a LPC2106-controller. One such project is the
blinky_irq
> example from Keil which should demonstrate the use of interrupts and of
the
> LPC2xxx vectored interrupt controller. I'm using gcc-3.2.1 with binutils
3.13.1
> and newlib 1.11.0 . So far I had no problems with these tools and I was
able to
> build and succesfully run some small demonstrator programs (without
interrupts)
> on my LPC2106 board. For the blinky_irq example program I use the linker
script
> and startup.s files (with adjustment for the Flash and RAM sizes of the
LPC2106)
> that came with the source code from Keil's download area. Since the
program
> didn't work I stripped it from all unnecessary functionality (main() is
> essentially an empty loop now) and simply let the timer ISR toggle a LED
on
> GPIO24. That worked initially, but after some time (~ 3 minutes) the LED
stopped
> toggling. I suspected that somwhere I'm loosing memory such that after
some time
> I'm out of RAM. Hence, I took a look at the disassembled code and saw that
the
> ISR is messing up the IRQ-mode stack pointer, loosing seven words each
time the
> ISR is invoked.
> Since the ISR entry and exit codes are automatically generated by the
compiler I
> suspect a bug in gcc. On the other hand, since this would be a very severe
> failure other users should have come across it, too. Does anybody of you
know
> that error (i.e. should I change to another gcc version) or am I missing
> something (e.g. gcc options)?
> Below you'll find the build commands used, the sources of the program and
the
> disassembled ISR code.
>
> TIA,
> Jens
[snip]

using arm-elf-gcc 3.3.1 I don't have this problem. Not that the interrupt
attribute needs to specify the type of interrupt ("IRQ", "FIQ","SWI" etc).

void __attribute__((interrupt("IRQ"))) SYS_10ms_irq_handler(void)
{
    TIMER2->status = 4; // clear timer int
    VIC->VectAddr = 0; // clear VIC
    tick_count++;
}

arm-elf-gcc -S -O -DUVDAS -mcpu=arm7tdmi sys_irq.c

SYS_10ms_irq_handler:
 @ Interrupt Service Routine.
 @ args = 0, pretend = 0, frame = 0
 @ frame_needed = 0, uses_anonymous_args = 0
 @ link register save eliminated.
 stmfd sp!, {r2, r3}
 @ lr needed for prologue
 mvn r3, #244736
 sub r3, r3, #940
 sub r3, r3, #3
 mov r2, #4
 str r2, [r3, #8]
 mov r3, #-2147483648
 mov r3, r3, asr #19
 mov r2, #0
 str r2, [r3, #48]
 ldr r2, .L3
 ldr r3, [r2, #0]
 add r3, r3, #1
 str r3, [r2, #0]
 ldmfd sp!, {r2, r3}
 subs pc, lr, #4
.L4:
 .align 2
.L3:
 .word tick_count

this include the correct subs pc,lr,#4 that performs a return from interrupt
(swapping back to old stack).

regards
Peter