I´m developping a cd-dvd driver ,i already did a fast reading of the 1000 pages of multimedia scsi commands, but somethings are not clearly explained, the problem that i have now is that when i change the cd disc
i have to reset the driver and retry many times until it works, so i think that perhaps i forget to send some comand to correctly initialize the unit.
some idea about this problem?
after many tries everithing goes fine, all commands works and i can read
data disc or play music disc.

As far as i know this is the normal,as my driver does the same, but i do not do reset, i thought it may be not doing the reset, but as you get the same problem and do it must not be that.
As some cd driver seem to work better than others, dvd driver need more try than cd drives also read cd-rw is better than cd-r, you need to try then a delay and try again about 5 time if not give error.

I think windows/ linux does the same, but hides it .

For writing a cd driver i´m reading this doc: mmc4r05a.pdf
have done a few tests with some commands, and have a few problems with ´GET CONFIGURATION´ command. When this command is send to the device, the reponse is variable length, i read the reponse data testing bit 3 of ide status port, the device sends 60 bytes of data, but the data lenght in the feature header descriptor is 96 bytes,what is happening?
all the other data is ok with the documentation.
I have already tried to add delays or force to read 96 bytes.

I do not use that command,but if you do the number of byte to read and acknowledge them and you still only get 60 bytes, then maybe the doc wrong as a lot of doc on ATAPI are full of mastakes.

These are interesting things
i havent seen complete informations on ata read write either,

but you can realize the reading retries with:
spinning up disc,
focusing and seeking optical head to track 0, getting toc.

there must be a disk spin up, seek complete, disk read function somewhere.

my mistake was to use the wrong format in numbers ,scsi uses motorola format, not intel. Now the problem is solved.

Thats a easy mistake to make .