Paul,

    I have a Micropolis 3391 on the external bus that is running at 6.25 MHz (I
believe this is the max it can run because of the clock input to the 53c94). So
NetBSD is pushing the bus past its 5.0 MHz limit. This is clearly stated in the
boot messages when the scan is done. If you are not seeing anything then your
scanner is not running sync.

    I wonder if you could be seeing some kind of problem with that descriptor
based DMA beastie (aka Grand Central) that sits in front of the external SCSI
chip?

    Are there any macros you can set in the 53c94 driver to give more verbose
details? What elese is on the external bus? BTW, I have an old Iomega bernoulli
drive on the external bus on my 9600 that seems to work fine (it is async only).

    Have you done any searches on the web to see if your scanner is a "bad scsi
citizen"? Maybe this scanner is pulling some stuff that is giving the NetBSD
driver for the external bus fits?

    How does it behave if you do a show-children from OF?

paul beard wrote:

> Hey,
>
> I am trying to work out if I can use SANE on my old PPC 9500, and
> seem to be running into some issues. If there is anyone who answer
>   some questions about how the external SCSI bus works --
> specifically if Apple engineered some idiot-proofing into it that
> SANE may not be aware of -- please let me know.
>
> Here's what we're seeing: the external bus (this box has two built
> in) sees the scanner and tries to use it, but gets reset during
> the scan, and then it's lost until I restart it. There are some
> miscommunications between the scanner library (SANE) and the
> kernel: where the scanner says it's returning 161 bytes of data,
> we only get 160.
>
> A related note from one of the developers who has been looking at
> this:
>
> > A more general SCSI question: (I assume that the folks who adapted
> > NetBSD to the Apple hardware know this, but let us be sure ;) The reason
> > that Apple installs two SCSI busses in many of their computers is to
> > have a fast internal bus for the hard disks; this bus needs the usual
> > careful setup: proper cabling and termination; for the external bus
> > Apple managed to design the interface in an amazing "error-friendly"
> > way. I have seen several absolutely wrong setups working flawlessly,
> > like a 1.5 m cable at the end of the bus without a device and without a
> > terminator. This can only work for slow transfer speeds, so I wonder if
> > the NetBSD kernel really ensures that the speed of the external bus is
> > really 5 MHz. Do you see anything related messages with dmesg or in some
> > log files?
>
> --
> Paul Beard
> 8040 27th Ave NE
> Seattle WA 98115
> 206 529 8400
>
> "Of ______course it's the murder weapon.  Who would frame someone with a
> fake?"