2 Feb
2013
2 Feb
'13
1:32 p.m.
On 02/01/2013 09:42 PM, Jeff Jonas wrote:
Long ago when SCSI was young
and just an 8 bit parallel bus,
Ampro littleboards advocated using the SCSI bus
for peer to peer communications, not just master/slave.
Did anyone else do that?
No rare was the need for multiple loosely coupled Ampros.
First the interface used by Ampro was a loose SCSI (pre SCSI spec!)
And it could be used as a generalized bidirectional parallel bus
or it could so SASI (sasi was the pre SCSI) and with the right code
it could do slow SCSI (programmed IO). I used it to connect to a
3.5" fujitsu 45MB SCSI drive. Worked well lots of code needed
the base drivers only did a very limited subset for use with the
Adaptec SCSI to MFM bridge board or the ST225N.
So there is no resemblence there to SCSI as we currently know it.
A fellow contacted me with this problem:
I have a couple of Kurzweil synthesizers (/samplers/sequencers):
K2000RS and K2600X . They have integrated floppy and SCSI HDDs
for storing configuration, composition and audio sample data.
They're actually 68000 CPUs with a Kurzweil OS,
managing IO among peripherals
(keys, SCSI, display LCD, MIDI, etc) and several proprietary DSPs.
But there's no serial/network/etc IO.
I'm interested in trying to use their SCSI
to interface them with a (Linux) PC somehow.
Any ideas? Like maybe some webpages
describing projects that have networked older
(preferably 68xxx) CPUs over their shared SCSI bus.
My understanding is that a Kurzweil and a Mac were sometimes configured
each as a SCSI device on the same SCSI bus as the HDD,
and either host could alternate accessing the HDD
once the other host was no longer issuing
potentially conflicting SCSI commands to the HDD.
I don't see how just read commands could conflict,
but perhaps the HDD wasn't able to multiplex commands
targeting different hosts in any overlap.
But evidently people were transferring samples
between Kurzweil and Mac this way.
[I replied privately about the problem
of multiple machines sharing a drive even if one is read-only]
any clues or hints?
Serious memory test here...
All SCSI devices have an address including the host and the maximum was 8
total (0-7). Also the bus assumed only one controller so all other
units were
slaves that could do no more than assert ATN
Early (that era) SCSI disks did not know who issued command as they were
slaves. Further they were FIFO serial command structure with minimal if
any command silo and the assumptuion that the command executed
produced results that went back to the only host controller.
Are you sure the bus was SCSI and not GPIB? GPIB was a multi talker,
multi controller, multi-listener bus that allowed for up to 31 devices
and was also a parallel 8bit bus.
Allison
thanks
-- jeff jonas