> So you think it is somewhere in esa.c, not in the higher audio driver
> (audio.c) or in the ac97 code?

Most definitely.

> I will need some guidance to help wade through it all, but am willing
> to help.  Can you give any suggestions about where to look or how to go
> about narrowing down the problem.

esa_trigger_{input,output} might be a good start.

> Can anyone verify that full duplex works with all the other audio
> drivers, especially including other ones that rely on the ac97 code?

I'm almost certain that it's not a problem with the AC'97 code. I only use
that for controlling the mixer with the Allegro-1 driver.

Regards,
Jared