[fpc-devel] Interrupt vector table generation

[Jeppe Johansen]

Den 07-03-2011 09:43, Mark Morgan Lloyd skrev:
> Jeppe Johansen wrote:
>> As I wrote a while back, I would like to make it easier to handle 
>> interrupts when using fpc for embedded work
>> The current solution is to use procedure variables with indirect 
>> jumps in inline assembler. While that works okay it takes up a lot of 
>> space on devices with lots of interrupts, and introduces unnecessary 
>> interrupt latencies
>>
>> An idea would be to use weak linking, and while it's possible in 
>> external assembler, a nicer solution would be to handle it in 
>> procedure directives. That would mean addition of some functionality 
>> that is generally unportable and ambiguous across platforms. So I've 
>> moved away from this idea for now
>>
>> A better idea, I think, is to use the old interrupt procedure 
>> directive. For some embedded platforms simply allow also specifying a 
>> interrupt vector/index after the interrupt keyword. Ex:
>>
>> procedure USARTRxInterrupt; interrupt 10;
>> begin
>>    // Handler code
>> end;
>>
>> And from that automatically generate an interrupt vector table in the 
>> compiler when compiling a program. Those tables of course look 
>> different for each targetted architecture, but usually they are 
>> either tables of branch instructions or addresses. For embedded work 
>> you'll specify the controllertype anyway, and that way know how large 
>> the table is, and what kind of vector to use
>>
>> Further, a future benefit of using the interrupt keyword could be 
>> generation of procedure exit code. Some platforms need a special 
>> "return from exception/interrupt" instructions at the end of 
>> interrupt handlers
>
> I'm not sure that this belongs in a core language, because (a) the 
> whole concept of interrupts is non-portable
You could say the same about perfectly valid pascal code writing and 
reading from memory mapped hardware registers

On those platforms this change is aimed for(ARM, AVR, AVR32, etc), the 
interrupt vector table is usually mapped into ROM at address 0. There 
might not be a way to change it, so the values in it are constant. All 
interrupt vectors have a specific purpose

It's not aimed for complex architectures such as x86 where interrupt 
vectors aren't constant