non aligned DMA transfer attempted

Alexander Motin mav at
Fri Sep 4 06:50:51 UTC 2009

Ryan Rogers wrote:
> Alexander Motin wrote:
>> Ryan Rogers wrote:
>>> I'm having a bit of a problem getting my DVD drive(s) to work 
>>> correctly.   I'm trying to transfer my DVD collection to my media 
>>> server, but whenever I run vobcopy, /var/log/messages gets spammed with:
>>> acd0: FAILURE - non aligned DMA transfer attempted
>>> acd0: setting up DMA failed
>>> I added a bit more information to the first message to see if I could 
>>> figure out what was actually going on.  request->data was 0xd40e0c37, 
>>> ch->dma.alignment was 2, and request->bytecount was 2048.
>> Actually I don't understand what for this check was made there. It is 
>> busdma infrastructure business to implement buffer bouncing to manage 
>> requested alignment. But this check enforces application level to 
>> bother with this. Usually it works fine, as memory often allocated 
>> aligned. But probably here is some specifics in your application. 
>> Could you try to just to comment-out that request->data check?
> I commented out that part of the check, and it worked in the sense that 
> it didn't spit out any errors at me, but I'm not 100% certain that the 
> data isn't getting corrupted.  I tried ripping two discs.  The first is 
> completely corrupted, the second appears to be fine on first glance. I'm 
> going to try a couple more discs to see if maybe the first one was just 
> bad.


> Also, one other thing that I noticed that seems odd is this:
> acd0: DVDR <TSSTcorp CDDVDW SH-S223L/SB02> at ata6-master SATA150
> ....
> cd0: <TSSTcorp CDDVDW SH-S223L SB02> Removable CD-ROM SCSI-0 device
> cd0: 3.300MB/s transfers
> I timed how long the first disc took to rip, and it seems to match that 
> reported speed.  "Working but slow" is certainly better than "not 
> working", but my speeds in Windows using DVD Decrypter on the same disk 
> are at least 3 times faster, bursting up to about 5 times faster.

It's just a small atapicam misfeature. It doesn't translates SATA modes 
to CAM speeds. It's only cosmetics, it shouldn't be important.

Alexander Motin

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