Future Domain SCSI controller for AT bus

[Chris Lewis]

In article <2008 at spdcc.COM> dyer at spdcc.COM (Steve Dyer) writes:
>In article <213 at ispi.UUCP> jbayer at ispi.UUCP (id for use with uunet/usenet) writes:
>>The problem is not Xenix, but the way IBM designed the AT.  What happens
>>is that most controllers use the same interrupt.  The AT cannot support
>>multiple devices with the same interrupt.  Also, they both might be using
>>the same address space.  Either or both of these situations will cause 
>>problems.  Perhaps some of the hardware types will be able to shed some
>>more light on the matter.
>
>Neither is the problem.  The IRQ is settable (3 or 5, neither of which
>is used by the AT disk controller), 

You're right - the 830 doesn't clash with the AT disk controller - it
clashes with COM2 (3) or LPT2 (5) respectively.  Therefore, you have to
somehow disable one or the other in Xenix.

It *is* possible to run two devices on the same interrupts, but it
requires a little robustness from the two drivers, sometimes a little
hacking to the configuration, *and* (gawddamn IBM!) pull down resisters
on the interrupt lines on the bus.  (you ever heard of upside-down
open collector gates?)

The main difficulty with the 830 is that it's so darn stupid.  The
device driver even has to toggle the ACK/NACK bits to transfer a single
byte.  Gack.  Performance is moderately awful compared to other
controllers.   Recommended: AHA1540 from Adaptec, or make the plunge
to ESDI and use the DPT controllers (one of which actually emulates
a WD1003, so would use the normal hard disk drivers).
-- 
Chris Lewis
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