Isochronous Parallel SCSI?

Duncan Penman penman at
Thu Oct 6 22:06:10 PDT 1994

  Video servers are upon us, and I think we need to address the problem 
of guaranteed bandwidth and rate of delivery on the parallel bus.  At 
the X3T10 meeting in Houston there was mention of a proposal several 
months back for a set of isochronous (Read/Write?) commands.  I'd 
appreciate a pointer to that if anyone knows where a copy exists.

  A more fundamental question is whether this should be handled at the 
command level or the protocol level.  I believe P1394/SBP handles 
isochronous setup in the physical and protocol layers, with ordinary Read 
commands being executed either asynchronously or isochronously based on 
the FIFO address the SCSI Command CDS is sent to.  My preference for the 
parallel interface is to also try to accomplish isochronous support 
without changing the command set.

  I can envision a couple of ways to approach the design, one based one 
the synchronous negotiation model and the other based on the idea of a 
high priority timeslice master on the bus.  Neither is pretty.

  This is not as pressing as getting a new basic draft of SIP out, but 
I'd like to start exploring the subject with the object of an early-1995 
proposal.  Anyone out there interested?

Duncan Penman
Zadian Technologies
penman at

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