Harmony is a really simple little audio device which is a part of the LASI ASIC found on many early PA-RISC boxes. Apparently it is programmatically equivalent to the Vivace audio device found on even earlier PA-RISC machines.
The operation of the hardware is mostly quite simple and elegant. We load the next page address first, and DMA gets automatically started when we load the current page address. An interrupt is generated whenever the hardware reaches a page boundary, allowing us to load the next page address. Unfortunately it is not designed with separate playback and recording controls, we must always do both. Thus when we only want to record, we playback a silent buffer; and when we only want to playback, we record to a graveyard buffer.
[TODO writeup something about the registers & mixer]
The chip is fully documented in the LASI ERS.