New message proposal for Fast-20

Tak Asami (Asami asami at
Fri Jul 8 19:07:24 PDT 1994

This proposal is really generated by Jeff Stai, and I am submitting this
on his behalf.  Needless to say, I agree with his proposal, and I hope
all of you would consider it.

ref 6.1 of Fast-20 minutes.
We do have a problem trying to specify exactly 20MXfr/sec using the
existing synchronous negotiation message. A few not-so-clean fixes were
discussed, but I believe none received much support so far.

It seems to me that, given that most newer devices are now robust in
regards to unknown messages, it would not be unreasonable to propose a
new flavor of the sync xfer message to handle the problem with 4 ns

Something like:

byte     value     description
 0        01h      extended message
 1        05h      extended message length
 2        04h      EXTENDED SYNC TRANSFER REQUEST code
 3        mm       Transfer period MSByte
 4        mm       Transfer period LSByte
 5        nn       REQ/ACK Offset MSByte
 6        nn       REQ/ACK Offset LSByte

Transfer period would be in 1ns or 0.1ns increments.

I suppose this actually belong to SIP document, but most SPI folks should
be interested on this.

Can I get any response?

Tak Asami *AND* Jeff Stai ================================================
Western Digital Corporation
I/O Product Engineering
(714)932-7621 or 7644
(714)932-6496 Fax (we share the fax machine!)
asami at, stai at

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