Problem with pokey sound channels 3+4

[bugbiter]

Hi everyone,

 

I'm doing 4 channel sound in Assembler for the first time.

 

It's quite easy actually, you've got AUDF1-4 for the pitch,

AUDV1-4 for sound type (bits 4-7) and volume (bits 0-3)

Then, you've got AUDCTL where you can pair chan 1+2 or 3+4 to 16bit resolution, and other freaky stuff. I have that set to zero.

 

Now, in Altirra everything works fine. But on my real 130XE channels 3+4 seem to be muted - all you can hear are the buzz of the volume steps going up and down.

At first I thought there was something wrong with my code for chan3+4 but when I simply reversed the equate numberings for AUDF and AUDV (4 to 1, 3 to 2, 2 to 3, 1 to 4) so chan 3+4 play the sound code for chan 1+2, it is still channels 3+4 that are silent.

 

As I said, AUDCTL is zero, so there is no fancy stuff involved and all channels should work the same.

 

I tried another program of mine which uses only sound channel 1. If I set it to channel 4 there's no sound! WTF?

 

I don't get it - is there some other register that does something strange to chan 3+4 on default?

[Rybags]

It's probably thanks to a bug in the XL OS. After SIO it doesn't set things quite right which can affect audio.

 

In your program, set SKCTL to 3 - also set SSKTCL (the shadow) - addresses are $D20F and $232.

Also set AUDCTL to 0 ($D208) - probably just easist to clear all the sound related registers first, just put zeroes in $D200-$D208 at the start of your program.

[bugbiter]

Thanks! I'll try that.

[bugbiter]

Thanks guys. That does it. I read elsewhere now that you generally have to re- init pokey after io. Lesson learned.

[Creature XL]

Thanks guys. That does it. I read elsewhere now that you generally have to re- init pokey after io. Lesson learned.

 

This is also stated in the ABBUC contest rules. There are other nice tips as well

Oh and yes, I learned the hard way. MJO had the same problem