Jeffry Loucks wrote:
>
> The 68EZ328 indeed supports a mulu instruction, but you'll notice it is a
> 16x16 operation. In other words, a mulu.S. You were trying to use a mulu.L,
> which is not supported by the EC000 core.
>
> Your original callback uses a global value to locate the multiply code
> [move.l [EMAIL PROTECTED](%a5),%a0]. It is found relative to the A5 register,
> which is reserved as the globals context register. If the A5 register is not
> correct when CallbackPeckAudio() is called, you will not be able to
> correctly locate the desired global value. In other words, the calling code
> may have it's own globals context, which could mean that the value of A5 has
> been changed to meet the calling code's needs, and is wrong for your needs.
>
> If this is the case, you should either 1) not refer to globals in your
> callback, or 2) pass your A5 value to the callback and use SysSetA5() to
> temporarily set A5 for your use.
>
> This is all best accomplished by creating a structure containing everything
> needed by the callback, and then passing the address of the structure to the
> callback as a userdata pointer. The structure could contain your own A5
> value, giving you full access to your normal globals, or it could contain
> everything needed without globals, or some combination.
>
> You already do the structure bit with "struct PeckAudioType". You could
> either add your A5 value to the structure, or add a reference to the global
> in the structure. Whatever works best for you.
>
> If you'd like info on a (32x32).L, that's another email.
>
> Sorry so long winded.
>
Sorry?? Your response was very helpful.
For the sake of closure, the working code follows.
typedef struct PeckAudioType {
SndStreamRef streamRef;
UInt32 fileSize;
UInt32 fileOffset;
FileRef fileRef;
UInt32 bufferCount;
UInt32 s;
UInt32 a;
UInt32 b;
UInt32 a5;
} PeckAudioType;
Err CallbackPeckAudio(void *pUserData,
SndStreamRef stream,
void *bufferP,
UInt32 frameCount)
{
Err err;
UInt32 a5callback;
PeckAudioType *pPeckAudio = (PeckAudioType *)pUserData;
/* Read next sound stream buffer from file. */
err = VFSFileRead(pPeckAudio->fileRef, frameCount*2, bufferP, NULL);
a5callback = SysSetA5(pPeckAudio->a5);
pPeckAudio->a *= pPeckAudio->b;
SysSetA5(a5callback);
- - -
Thanks again,
Greg
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