On 2005-04-05, Greg Sepesi <[EMAIL PROTECTED]> wrote:
> I'd like to implement a UInt32 x UInt32 multiply (discarding the most
> significant 32 bits of result) in a callback for a sound stream, but the
> multiplication is causing a fatal exception (on a Zire 31). From
> looking at the assembly language produced by gcc, the reason for the
> exception appears to be the attempted use of a global (not available in
> callback).
>
> Here's the applicable data structure and code:
>
> typedef struct PeckAudioType {
> SndStreamRef streamRef;
> UInt32 fileSize;
> UInt32 fileOffset;
> FileRef fileRef;
> UInt32 bufferCount;
>
> UInt32 s;
> UInt32 a;
> UInt32 b;
> } PeckAudioType;
>
> Err CallbackPeckAudio(void *pUserData,
> SndStreamRef stream,
> void *bufferP,
> UInt32 frameCount)
> {
> PeckAudioType *pPeckAudio = (PeckAudioType *)pUserData;
> Err err;
>
> /* Read next sound stream buffer from file. */
> err = VFSFileRead(pPeckAudio->fileRef, frameCount*2, bufferP, NULL);
>
> pPeckAudio->a *= pPeckAudio->b; /* LINE 8 */
>
> - - -
>
> The assembly language for Line 8 is:
>
> .globl CallbackPeckAudio
> CallbackPeckAudio:
> ...
> .ln 8
> move.l [EMAIL PROTECTED](%a5),%a0
> add.l #__mulsi3,%a0 /*JANE2*/
> move.l 28(%a2),-(%sp)
> move.l 24(%a2),-(%sp)
> jsr (%a0)
> addq.l #8,%sp
> move.l %d0,24(%a2)
>
> - - -
>
> Noting that changing the multiplication to addition causes an in-line
> calculation and allows the sound stream callback to work properly, I
> tried gcc's inline assembly.
>
> Err CallbackPeckAudio(void *pUserData,
> SndStreamRef stream,
> void *bufferP,
> UInt32 frameCount)
> {
> PeckAudioType *pPeckAudio = (PeckAudioType *)pUserData;
> Err err;
>
> /* Read next sound stream buffer from file. */
> err = VFSFileRead(pPeckAudio->fileRef, frameCount*2, bufferP, NULL);
>
> // pPeckAudio->a *= pPeckAudio->b;
> __asm__("
> move.l 28(%a2),%d0;
> mulu.l 24(%a2),%d0;
> move.l %d0,24(%a2);
> ");
>
> - - -
>
> However, that results in the compiler error: "invalid instruction for
> this architecture; needs 68020 or 68030 or 68040 or 68060 or cpu32 or
> 5200 or 5206e or 5307 or 5407 -- statement `mulu.l 24(%a2),%d0'
> ignored". That's a bit confusing because the MC68EZ328 User Manual
> lists a mulu instruction in its EC000 instruction set. I've never had
> to mess much with the prc-tools. Do I need to somewhere specify that I
> want gcc to produce MC68EZ328 instructions?
>
> Before I get into this any deeper, I'd like to ask how others have
> implemented multiplications from within callbacks.
>
> Thanks,
> Greg
>
The assembler in the m68k-palmos-gcc backend defaults to the bare-bones
m68000 instruction set. You can see this if you do 'm68k-palmos-gcc
-dumpspecs'.
As a workaround use the '-Wa,-m68020' option to force the assembler to
recognize the mulu.l instruction.
HTH
Ton van Overbeek
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