Hi Gino!

> I've been using FreeDOS for a while and it works great.

Nice :-)

> I'd like to write an Intel HDA driver for SCI games (Sierra quests).
> Ok, they work great under Dosbox, but I still prefer using plain DOS.

You could at least use dosemu :-p Much faster :-)

> I consider myself a good programmer, but I've never made any low-level
> programming or debug DOS programs.

Which programming languages do you write? At least part of your
driver can be written in C, but you might need Assembly language
as well, in particular if you want to take the tough route of
creating universal virtual hardware instead of a Sierra driver.

For debugging, I recommend using DOSEMU or, for even more lowlevel
stuff, BOCHS, but you can also try 386SWAT in pure DOS, maybe :-)

> Is there any book or information on the net I can start with?

Creating virtual hardware can be very hard, but if I understand
you correctly, Sierra games already have some sort of interface
for loading custom sound drivers? Then you can split your task
in two parts: Write something which makes any sound on HDA and
can be run from the command line. And write something which does
anything with the sound sent by a Sierra game and which can be
loaded as a Sierra driver. For example the latter can blink some
pixels on your screen or can use the PC speaker (port 61h) - any
noticeable activity will be enough to show you that your Sierra
driver does properly receive sound data from your game... The
command line thing could for example be based on MPXPLAY sources
and can play any simple noise you want - a sine, maybe with some
frequency sweep over time, will do perfectly :-).

Eric



PS: You can have a look at the sources of the ancient VSB
virtual sound blaster to see how complicated it is to create
some virtual hardware for SB1/SB2. Or look at the sources of
DOSEMU to see how a proper virtual SB16 can be implemented in
C. Of course DOSEMU uses Linux to send sound to your hardware
and to trap I/O access of DOS, so it only shows the "middle"
part of what a virtual soundblaster for DOS will need...



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