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AHCI CD-ROM driver for DOS (Developers)

posted by DOSferatu, minneapolis, mn usa, 21.12.2009, 16:45

> Thanks.
>
> > 1) there are no longer IO ports to access the drive. (1f0-1f7,
> 170-177, etc)
>
> Above are legacy ports, but there are also "native" IDE/SATA ports ...
sure, but all that means is that the decoding done at the old 1f0-1f7 are now relocatable anywhere in IO space and the BIOS/OS is in control of where they go. It's the same stuff, just in a different place. In AHCI that stuff is gone. It's all done via memory mapped access now.


>
> > so the drive does not appear as a standard hard drive anymore.
>
> So PIO / UDMA code won't find anyting ...
correct. You will not find a drive by poking any ATA type command via the typical "shadow register" block (LBA/command/device/features, etc registers) as you would with previous controllers. The registers still exist, but now reside inside a "FIS" which is a chunk of data in a table that the controller DMAs over to the drive. The nicest part is that it's all LBA mode, and it's all 48bit (actually 64 bit!) so finally, we have no size barriers, or at least not any realistic ones. 64bit is what, like 16,000TB or something insane!

>
> What performance do you get using INT $13 (IDECHECK) ?

10182 kB/S which is pretty respectable.

In AHCI mode, using my code, I did a similar test; 128k transfers (which should equate to IDECHECK's 256 sectors per transfer) and I topped out at 73MB/sec. :-D [same drive, same motherboard, same controller]

If I bump it up to a 4MB transfer size, I could get 76MB/sec. As I think I mentioned before, I believe you can do 32MB transfers (* 32 channels) and I can likely get a little bit more performance out of it, probably topping out at about 80MB/S. It's not quite an apples:apples comparison, but it's pretty easy to see the performance gain when AHCI is actually being used.


>
> So since it works well (just not very fastest) in DOS, the need for a
> driver is not "that bad" (not as bad as for sound) for now ;-)
I agree completely. It's plenty fast for normal usage, which is why I was thinking that making a clone type program, something that bypasses INT13, would be cool and useful.

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