Paced mode: DT DATA IN followed by DT DATA OUT

Richard Moore richard.moore at
Tue Jun 18 16:37:26 PDT 2002

* From the T10 Reflector (t10 at, posted by:
* "Richard Moore" <richard.moore at>
In paced mode, when ending a DT DATA IN transfer, according to SPI-4, "the SCSI target port shall end pacing by waiting for all REQs to be
responded to by ACKs then negate the REQ and P1 signals. After the SCSI target port stops asserting and negating REQ it shall not assert REQ
again until the requirements in 10.12 are met."

What SPI-4 doesn't seem to say is how long the target must wait after the last REQ negation before it changes any of C/D, I/O, or MSG. Is there
a minimum (other than zero)? If the target can change I/O simultaneously with the negation of REQ, what keeps the initiator from seeing the last REQ
of a DT DATA OUT phase as the first REQ of the following DT DATA IN phase (due to skew on the bus)?

 -- Richard Moore
    QLogic Corp.

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