Any NeoGeo authors have any tips about getting sound to work?

I have the Z80 running, and I pass the bios Z80 check. However, the ym2610 never gets a request to start an adpcm channel (I don't even care about the FM stuff yet).

I have the ym2610 timers running, and I've verified they are sending IRQs to the Z80. I'm giving the Z80 a NMI when the 68k sends a sound command.

I don't have much debugging capability on my target system, so it's hard for me to track down problems. Any insights would be very much appreciated.