Simple ARM timer interrupt question

I'm trying to get a very simple timer interrupt working in C on
Atmel's EB40A board. The processor is an Atmel AT91R40008. I'm using
the gnu tools from codesourcery (arm-none-elf-gcc etc). I have some
non-interrupt samples working. The interrupt is not working. LED1 (the
main loop LED) blinks, but the timer LED doesn't blink. I found this
sample on Atmel's web site but that loaded timer1_asm_irq_handler into
AIC_SVR5. I'd LIKE to load it with "time1_c_irq_handler" instead.
Could someone tell me if I can do that and how to get this simple
example working? Here's a link to the files: www.toadhaul.org/arm.php


Paul

Only thing I can think of right now is to look at the assembly language that
the compiler generates for the interrupt routine. Make sure it conforms to an
interrupt service routine. Most CPUs have a seperate return instruction for
regular subroutines and for interrupt service routines.

You didn't mention any compile or link errors/warnings so I assume it all goes
together ok.

> sample on Atmel's web site but that loaded timer1_asm_irq_handler into
> AIC_SVR5. I'd LIKE to load it with "time1_c_irq_handler" instead.
> Could someone tell me if I can do that and how to get this simple

You can't vector the interrupt direct to C. You need an asm reflector shim.

On 16 Nov 2004 17:10:59 -0800, larwe@larwe.com (Lewin A.R.W. Edwards)
wrote:

>> sample on Atmel's web site but that loaded timer1_asm_irq_handler into
>> AIC_SVR5. I'd LIKE to load it with "time1_c_irq_handler" instead.
>> Could someone tell me if I can do that and how to get this simple
>
>You can't vector the interrupt direct to C. You need an asm reflector shim.

Oh. I didn't know that. Do you have an example of how the asm
reflector should be?

Paul

"Lewin A.R.W. Edwards" <larwe@larwe.com> wrote in message
news:608b6569.0411161710.2f2299bc@posting.google.com...
> > sample on Atmel's web site but that loaded timer1_asm_irq_handler into
> > AIC_SVR5. I'd LIKE to load it with "time1_c_irq_handler" instead.
> > Could someone tell me if I can do that and how to get this simple
>
> You can't vector the interrupt direct to C. You need an asm reflector
shim.

well I have an ARM timer interrupt written entirely in C that uses the GCC
extension

void __attribute__((interrupt("IRQ"))) SYS_kbd_irq_handler(void)
{
    ...
}

I then stuff the function pointer into the VIC

works fine for me.


-- 
Peter.Dickerson (at)...

On Wed, 17 Nov 2004 14:24:32 GMT, "Peter Dickerson"
<first{dot}surname@ukonline.co.uk> wrote:

>"Lewin A.R.W. Edwards" <larwe@larwe.com> wrote in message
>news:608b6569.0411161710.2f2299bc@posting.google.com...
>> > sample on Atmel's web site but that loaded timer1_asm_irq_handler into
>> > AIC_SVR5. I'd LIKE to load it with "time1_c_irq_handler" instead.
>> > Could someone tell me if I can do that and how to get this simple
>>
>> You can't vector the interrupt direct to C. You need an asm reflector
>shim.
>
>well I have an ARM timer interrupt written entirely in C that uses the GCC
>extension
>
>void __attribute__((interrupt("IRQ"))) SYS_kbd_irq_handler(void)
>{
>    ...
>}
>
>I then stuff the function pointer into the VIC
>
>works fine for me.

I added a "shim" in boot.asm and tried that by loading the AIC_SVR5
register with the assembly routine. I had to modify the assembly code
to get it to assemble with arm-none-elf-as. But still no interrupts.
It did not even break in the assembly routine.

I switcheck back to a strictly C interrupt changing the function
declartion to the form of your Sys_kbd_irq_handler, but still no
interrupts. The program is running because the main loop is blinking
the mainline led.

It seems that I need to do something else to enable interrupts. Any
ideas? The current state of the test program is at
www.toadhaul.org/arm.php

Paul

> well I have an ARM timer interrupt written entirely in C that uses the GCC
> extension

What GCC version are you using?

"Peter Dickerson" <first{dot}surname@ukonline.co.uk> wrote in message
news:AaJmd.71$ze1.35@newsfe2-win.ntli.net...
> "Lewin A.R.W. Edwards" <larwe@larwe.com> wrote in message
> news:608b6569.0411161710.2f2299bc@posting.google.com...
> > > sample on Atmel's web site but that loaded timer1_asm_irq_handler into
> > > AIC_SVR5. I'd LIKE to load it with "time1_c_irq_handler" instead.
> > > Could someone tell me if I can do that and how to get this simple
> >
> > You can't vector the interrupt direct to C. You need an asm reflector
> shim.

Never heard of an asm reflector shim.

GCC allows the interrupt to be written in C by using the __attribute__
extension.

Search for __attribute__ on  http://www.freertos.org/portlpc2106.html.  The
FreeRTOS source code has examples for the serial port and a timer
interrupt - but for a Philips not an Atmel.

Paul Marcel <pama19800522@hotmail.com> wrote in message news:<2otmp01fpma8jf3gne9b853d9jshvadds1@4ax.com>...
> On Wed, 17 Nov 2004 14:24:32 GMT, "Peter Dickerson"
> <first{dot}surname@ukonline.co.uk> wrote:
> 
> >"Lewin A.R.W. Edwards" <larwe@larwe.com> wrote in message
> >news:608b6569.0411161710.2f2299bc@posting.google.com...
> >
> > You can't vector the interrupt direct to C. You need an asm reflector
> > shim.

Would that be the same as a veneer?

[snip blah blah]

> It seems that I need to do something else to enable interrupts. Any
> ideas? 

At some point in the output code is there something like
 MRS r0, CPSR
 BIC r0, r0, #I_BIT
 MSR CPSR_cxsf, r0
present? ARM's reset with global interrupts disabled,
Sprow.

> Never heard of an asm reflector shim.
> 
> GCC allows the interrupt to be written in C by using the __attribute__
> extension.

At the time I last wrote an ISR on an ARM platform - which was
probably at least 18 months ago - the GCC documentation said
explicitly that interrupts are not part of C, and are therefore not
directly supported. It was necessary to write a little snippet of ARM
assembler like:

fiq_handler:
stmdb r13!, {r0-r7, r12}
ldr r12, irqvector
bx r12
ldmia r13!, {r0-r7, r12}
subs pc, r14, #4

irqvector:
 .word c_fiq_handler


where c_fiq_handler is the C routine containing the actual ISR code.