Interrupts for Arm-elf-gcc

[Shaun Jackman]

Here's another way of doing it. Stuff a bunch of pc relative branches in
the IRQ vectors, and have your standard IRQ vector table immediately
following. Then, somewhere in your C initialization write
	IRQVector = IRQHandler;

In your code below, be careful not to confuse preprocessor symbols, and
linker symbols. The two don't know anything about each-other. Unless it
was defined used #define, or by passing -D to cpp, you cannot test it
with #ifdef. In particular, you can't check for the existence of
functions using the preprocessor. That has to be done with the linker.
You can do what you want using __attribute__((weak)) though. When I was
checking attributes, I also noticed that __attribute__((interrupt)) is
supported for the arm now. Check that out too!

Cheers,
Shaun


ldr pc, [pc, #24]
ldr pc, [pc, #24]
ldr pc, [pc, #24]
ldr pc, [pc, #24]
ldr pc, [pc, #24]
ldr pc, [pc, #24]
ldr pc, [pc, #24]
ldr pc, [pc, #24]

START:
	.word start
UDINSTVector:
	.word die
SWIVector:
	.word die
PABORTVector:
	.word die
DABORTVector:
	.word die
RESERVEDVector:
	.word die
IRQVector:
	.word die
FIQVector:
	.word die

die:
	b $

start:
	; your code starts here


On Wed, 2003-07-23 at 02:26, David Mc Kenna wrote:
> Hi Shaun,
> 
> Thanks for the reply. Just one or two questions with your code.
> 
> For ARM, the first few lines of code are your Interrupt vectors which look something
> like this
> 
> b 	start    	SVC	0x00
> b	UDINSTHandler	UND	0x04
> b	SWIHandler	SVC	0x08
> b 	PABORTHandler	ABORT	0x0C
> b	DABORTHandler	ABORT	0x10
> b	RESERVED\n"                 
> b	IRQHandler	IRQ	0x18
> b	FIQHandler	FIQ	0x1C
> 
> When an interrupt occurs, e.g. an IRQ, the core jumps to 0x18, switches to ARM
> if in thumb mode, and enters IRQ mode, which gives us access to the IRQ bank
> of registers. As the location is only one word in size we require a branch to
> another location, our IRQHandler. This code then executes our interrupt. 
>    The problem I have is that I don't want to always have to go in and manually
> write IRQHandler to jump to the function in C. What I would like to do, as it
> seems interrupts haven't being implemented in C is to something along these
> lines:
> 
> IRQHandler:
>        #ifdef IRQ_Interrupt
> 	       bl IRQ_Interrupt
>        #endif
> 
> What I hope this will do is the if a function written in C is present, that
> it will include this code ( bl IRQ_Interrupt ) in my IRQHandler. But when I
> do not write the function IRQ_Interrupt, it will not.
>     The above code works for when the function is written in C but when I remove
> it I get the following error:
> 
> interrupts.o: In function `IRQHandler':
> interrupts.o(.text+0x38): undefined reference to `IRQ_Interrupt'
> collect2: ld returned 1 exit status
> 
> Any help is appreciated,
> 
> Thanks,
> Dave



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