Re: [avr-gcc-list] GCC guru question (progue/epilogue sequences)

[Lai Kang Tin]

So everytime I upgrade the GCC, I have to change and recompile the GCC
adding a "nonret" Non-return attribute, which is identical to "naked"
but setuping the frame properly for local vars.

Kang Tin LAI

On Tue, 9 Jul 2002, Larry Barello wrote:

> In my RTOS (www.barello.net/avrx) I do the same thing you do.  Since
> GCC allocates up to 8  bytes of locals out of registers, kernel
> functions have the restriction that there be no more than 8 bytes of
> locals and you don't do anything that requires a frame (e.g. take the
> address of a local).
> 
> The NAKED attribute is unfortunate in that it doesn't set up the
> frame.  What is really needed is a "No Return" attribute so that
> registers are not saved by GCC and the RTOS can handle context
> switches without chewing up so much SRAM.
> 
> In assembler, where I control everything, AvrX runs comfortably in a
> 2313. With GCC AvrX needs an 8515 to do useful work since each context
> needs, at a minimum, 35 bytes before any that GCC uses.
> 
> Note: as soon as you call a function (from your task or interrupt
> handler) you get a valid frame and GCC pushes a bunch of registers
> that are likely unused at the top (naked) level.
> 
> Cheers!
> 
> ----- Original Message -----
> From: "Marko Panger" <address@hidden>
> To: <address@hidden>
> Cc: "AVR Mailing List" <address@hidden>
> Sent: Tuesday, July 09, 2002 2:23 PM
> Subject: Re: [avr-gcc-list] GCC guru question (progue/epilogue
> sequences)
> 
> 
> HI again !
> 
> My INT handler looks like
> 
> RTOS_INTERRUPT(VECTOR_NUMBER)        /*naked attribute*/
> {
>     uint16_t var1;        /* this is a variable used by the user*/
> 
>     IntEnter();        /*here I save registers*/
> 
>     User code bla...bla;
>     bla;
>     bla;
> 
>     IntExit();        /* here I    swap context*/
> }
> 
> As you can se I am doing a sort of pro/epi by my own. I should save
> the entire context in IntEnter() because the user code could make an
> another task ready to run, so the context is swapped in IntExit(). Now
> the extra code generated by the compiler is redundant and more - it
> wastes ram (PUSH, POP).
> 
> After IntEnter() Y and the SP are the same. My prologue sequence
> should be:
> 
> in r28, SPL
> in r29, SPH
> sbiw r28, NUMBER OF BYTES REQUIRED BY USER LOCAL VARIABLES
> out    SPL, R28
> out    SPH, R29
> 
> ----------------------------------------------------------------------
> ---------------
> Anyway I have just solved the problem with a little trick:
> 
> RTOS_INTERRUPT(VECTOR_NUMBER)        /*naked attribute*/
> {
>     IntEnter();        /*here I save registers*/
> 
>     UserFunction();
> 
>     IntExit();        /* here I    swap context*/
> }
> 
> void UserFunction(void);
> 
> Thanks for helping me !
> 
> Regards,
> Marko P.
> 
> 
> 
> ----- Original Message -----
>   From: Marc R. Wetzel
>   To: Marko Panger ; AVR Mailing List
>   Sent: Tuesday, July 09, 2002 11:05 PM
>   Subject: RE: [avr-gcc-list] GCC guru question (progue/epilogue
> sequences)
> 
> 
>   Did you had a look at ethernut? Something very useful is already
> there. This project
>   looks always for contributors.
> 
>   To your question:
> 
>   if an interrupt occurs your kernel has no chance to save any
> registers. so the pro/epilogue is very helpful.
>   your kernel will be interrupted and it is not clear -- when.
> 
>   Look at the ethernut-way: it uses a kind of wrapper for any possible
> interrupt source available.
>   and if you attach an real interrupt-handler to it, it will be
> called.
> 
>   Hopefully I understand your question right...
> 
>   /Marc
>     -----Original Message-----
>     From: address@hidden
> [mailto:address@hidden Behalf Of Marko Panger
>     Sent: Tuesday, July 09, 2002 10:56 PM
>     To: AVR Mailing List
>     Subject: [avr-gcc-list] GCC guru question (progue/epilogue
> sequences)
> 
> 
>     Hi all !!
> 
>     I realy hope somebody could answer the following question. I will
> try to explain the situation and my problem.
> 
>     So... I am writting a RTOS and I would like to have interrupt
> handlers written in C language. If I define a function as a INTERRUPT
> or SIGNAL the compiler generates the prologue/epilogue sequence
> automaticaly. But I don't need this. Registers saving an restoring is
> managed by my kernel.
> 
>     There is another possibility. I could decalre the interrupt
> function with NAKED attribute. This would be fine for me since the
> compiler doesn't generate the prologue/epilogue sequence. But here
> comes the problem. What will happen if I decalare some local variables
> wich are putted on the stack ?
> 
>     I was wondering if is possible to write my own pro/epi sequences ?
> How will I now how many variables are putted onto the stack ?
> 
> 
> 
> 
> 
> avr-gcc-list at http://avr1.org
> 

K.T.LAI
address@hidden


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