Advice on writing driver

[Adrian McMenamin <adrian@mcmen.demon.co.uk>]

I have asked some the questions below in piecemeal form before and only
occasionally got an answer, so i'll go through it all now and see if you
can help.

I am writing a driver for the Sega Dreamcast. Years ago I wrote an OSS
driver but the sound dma had not been reversed then so it was slower and
tended to lock the system.

On the Dreamcast (DC) sound the main CPU is an SH4 but there is a
separate low powered ARM7 to handle sound (PCM). The ARM7 has its own
memory space which is directly accessible to the SH4 only through a FIFO
like gateway (so slow) unless DMA is used.

The ARM7 also has to have its own program to be told how to play the
sound (this looks like firmware to the SH4).

The driver currently allocates a buffer in the main SH4 memory (using
the DMA buffer allocation APIs). This is then transferred to the ARM7
space using DMA.

The ARM7 code raises an interrupt to the SH4 whenever it plays 4096
bytes of the sound - ie every period.

What should my pointer callback return? the number of bytes/frames still
to be transferred from the DMA buffer to the ARM memory or the number of
bytes/frames still to play, or what?

Adrian



-------------------------------------------------------
This SF.Net email is sponsored by xPML, a groundbreaking scripting language
that extends applications into web and mobile media. Attend the live webcast
and join the prime developer group breaking into this new coding territory!
http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642