UDMA vs. VIA 82C686B

Lokadamus Lokadamus at gmx.de
Fri Jan 2 16:44:11 UTC 2009

Raphael Becker wrote:
> Hi all,
> I have had some problems with a VIA 82C686B UDMA100 controller with an
> attached 2.5" Harddisk (Samsung-foo, 40GB) running 7.1-RELEASE (GENERIC):
> UDMA-access is not possible even tough the HDD is able to do (in my
> Laptop) and the controller claims to support UDMA100. 
> I tried a CF-Card with the same hardware running 6.2 or 6.3-RELEASE with
> the same effect: some bad g_vfs-errors.
> I got around this problem by adding (at least one of) the lines to 
> /boot/loader.conf:
> hw.ata.atapi_dma=0
> hw.ata.ata_dma=0
> Is this a known issue? 
> Is there a workaround/patch for UDMA on this VIA-chipset?
> Do you need more details on it?
> It's kind of difficult to get the exact errors, because hw.ata.* seems
> to be a read-only ("boot-only") sysctl and I have limited (serial)
> access to the box. In case of hw.ata.ata_dma=1 I'm not able to unset
> this value in /boot/loader.conf because I cannot write to the disk
> because of the udma-errors then. 
> Regards
> Raphael
Have you look for a bios update for the mainboard?

Chipset 82C686B was buggy, known as 686B-Bug.


More information about the freebsd-hardware mailing list