ATA driver not as good in 4.8 as 4.5?

[Stephen McKay]

I have a Lite-On 24102B burner on an Epox 7KXA (VIA 686A southbridge) 
together with a few SCSI disks.  I recently upgraded from FreeBSD 4.5
to 4.7 then almost immediately to 4.8.  I've had trouble with the burner
since.

With FreeBSD 4.5, I used "sysctl hw.atamodes=---,---,dma,---" to set
the burner to DMA.  Everything then worked fine.  As far as I know it
was using UDMA33.  That's what the BIOS said it was using anyway.

With FreeBSD 4.8 I use "hw.ata.atapi_dma=1" at boot.  This then tells
me it is using UDMA33.  Unfortunately, I then often get this:

    acd0: READ_BIG - HARDWARE ERROR asc=0x08 ascq=0x03 error=0x00

I think this means a DMA error.  (PS why not say what it is?)

If I use atacontrol to downgrade to WDMA2, it works flawlessly (though
somewhat slower than it does in UDMA33 mode).

So, was 4.5 setting my hardware to WDMA2 when I thought it was doing UDMA33?
Has 4.8 introduced bugs that weren't in 4.5?  Is there another setting I've
missed?

Cheers,

Stephen.