Trouble using 16-bit POKEY sound on Atari 7800

[Synthpopalooza]

I've posted this over in the Atari 8-bit/5200 forum, but maybe somoene on here can help too ...

 

I'm doing the music for a game (PacManPlus's Bentley Bear) and the situation is that there will be in-game music, and also title screen, end level, boss defeat, and end game music.

 

During the in-game music, we're using channels 1 through 3 for music, channel 0 for the game sounds.

 

During title screen and other music, I want to use POKEY 16-bit mode to get the extended bass range. So basically, this means storing $50 in AUDCTL, joining channels 0 and 1, clocking the combined channel at 1.79 mhz. AUDC0 is not used so we're storing $A0 there, the frequency is controlled from AUDF0 and AUDF1, in a low-byte high-byte fashion to get 16-bit range, and the volume is controlled using AUDC1 which starts with a value of $A7 (for pure tones).

 

The problem is, this seems to work ok on the emulator (ProSystem 1.5) but not on real hardware. I am attaching the 7800 .asm code for a song below. It may be a 7800 issue, but maybe someone can look over the code and see if we missed something.

 

How it works, is that there is a channel table, a control volume table (which has AUDC0-AUDC3 values) and a note and duration table for each channel. The routine is supposed to go through each note, and decrement the volume on each note according to the duration. When we're in 16 bit mode, $A0 (distortion 10 volume 0) gets stored in AUDC0 so that we're not using that channel for any volume changes. The player routine has a logic to where it checks for this value then skips over any volume commands. What seems to be happening is, it plays properly on the emulator, but on real hardware the 16-bit channel is silent.

test16k.asm

Edited June 6, 2013 by Synthpopalooza