On Sun, Nov 02, 2003 at 06:39:26PM +0000, David Laight wrote:
> > > Could you try to force it to 1-sector PIO transfer ?
> > > Just force wd->sc_multi to 1 in wd.c:wdattach() line 326
> > 
> > This fixes the problem.  So I guess the Samsung cards are lying when they
> > claim to support 4-sector transfers?  Or is there a bug in the NetBSD driver
> > or something?
> 
> (not having looked at the code)
> 
> What does 'wd->sc_multi' control?
> IIRC there are two different commands, one for 'normal' reads and one
> for multi-sector reads.  However a 'normal' read command can transfer
> many sectors.
> 
> The multi-sector read reduces the number of interrupts by transferring
> data in blocks of sectors (instead of single sectors).
> I wouldn't have thought that multi-sector reads would make a big difference.

FWIW, in a conversation I had with a SanDisk firmware engineer long ago,
he said that with their firmware, at least, the multi-sector-read command
was much more efficient.

Thor