How to disable UDMA for HDD?

[Nathan Kinkade]

On Mon, Aug 09, 2004 at 11:10:40AM +0200, Stevan Tiefert wrote:
> Hello,
> 
> when I try to install FreeBSD 5.2.1 on my computer with HDD on ata0-master and 
> CD-ROM on ata0-slave I got five interessting messages during the 
> boot-process:
> 
> ...
> ad0: 4124MB <SAMSUNG VA34323A> [8938/15/63] at ata0-master UDMA33
> ad0: TIMEOUT - READ_DMA retrying (2 retries left) LBA=8446347
> ad0: TIMEOUT - READ_DMA retrying (2 retries left) LBA=0
> ad0: WARNING - READ_DMA interrupt was seen but timeout fired LBA=8446347
> ad0: WARNING - READ_DMA interrupt was seen but taskqueue stalled LBA=8446347
> 
> then the computer stops and he resists in this state till now...
> OpenBSD "downgrades" this DMA-thing automaticly and the CD-ROM seems not 
> supporting UDMA and I assume to set at bootphase 3 a device.hint but I don't 
> know which one?
> 
> With regards
> Mr.
> Stevan Tiefert

Here are the two pertinent sysctl variables for your ATA hard disk and
CDROM, respectively:

hw.ata.ata_dma: 1
hw.ata.atapi_dma: 0

These variables are read only once the kernel has been booted, so if you
want to try setting them manually you'll have to put them into
/boot/loader.conf as something like:

hw.ata.ata_dma=0

Nathan
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