Hi, I've got some questions on IDENTIFY DEVICE and IDENTIFY PACKET DEVICE commands:
1. Should I always check for BSY and DRQ set to zero before writing Device register (or other)?
2. Should I implement DEVICE RESET before identification for HDD and CD/DVD-ROM?
3. Why does WinXP set ERR to one after IDENTIFY DEVICE? Everything goes fine in DOS...

If your talking about what i think your talking about then YES.
I have read you should, but i do not and have had no problems, but i may add it later. No driver i have made for my OS, will work in WIN98 or XP, also i could not get commands like IDENTIFY DEVICE to work in pm, so i call that command in realmode on boot up, but call SendAtapiPacket etc, in pmode, so my driver is in two parts a RM part and a PM part.

PS: A basic ATAPI driver comes with my "CdPod" see here: http://board.flatassembler.net/topic.php?t=2164&start=50

NOTE: I was called ASHLEY4. then.

Do I need to perform 2ms delay after EXECUTE_DEVICE_DIAGNOSTIC? It seems that it goes fine without the delay, but according to ATA-ATAPI spec. it should be done?

You can not rely on the ATA-ATAPI spec, as there are many, many mistakes in the many ver, i have not my driver here so i do not know off hand, but if it work keep it with no delay, if you have a problem latter try with a delay.