nearly-lockup at boot with DMA enabled on DVD-drive

Søren Schmidt sos at
Tue Oct 5 09:20:25 PDT 2004

Roman Kennke wrote:
> Hi list,
> I am trying out the very latest BETA7 on my Fujitsu Amilo A laptop. I am
> experiencing problems with DMA on my DVD drive. I remember that with
> 5.2.1 and IMO also with BETA4 the DVD drive acd0 was set to PIO4. That
> was ok, because DMA would not work properly when forced (although DMA is
> supported by the DVD drive and the motherbord).
> Now with BETA7 (and BETA6 which I tried before) the drive is set to
> DMA33, which apparently does not work ok. This leads to an extremely
> long pause at boot time. I first thought this will lock up, but after
> several (5-7!) minutes, the boot proceeds (with the DVD drive not
> working :-( ). When I manually disable DMA in loader.conf everything is
> ok. I would really like to have DMA working (good solution) OR detected
> as PIO4 (bad solution) in FreeBSD-stable.

Well, it was decided to use DMA as default when the drive says it can at 
least UDMA33, so thats why it changed.

Now as to why ATAPI DMA doesn't work for you I have no easy answer, it 
can be chipset, device firmware, ATA driver or any combination of those. 
Did it ever work in DMA mode under FreeBSD ?
The Acer chip should be DMA capable but we might need to twiddle a few 
config bits to make it work, I'll look at it when I get the time, if too 
long passes please ping me again ...


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