Future Domain SCSI controller for AT bus
Chris Lewis
clewis at ecicrl.UUCP
Fri Oct 14 14:04:18 AEST 1988
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
{uunet!mnetor,yunexus,utzoo}!lsuc!ecicrl!clewis
(or lsuc!gate!eci386!clewis or lsuc!clewis)
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