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
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