SPI-3 & Packetized

Richard Moore r_moore at qlc.com
Mon Jan 18 14:38:24 PST 1999

* From the T10 Reflector (t10 at symbios.com), posted by:
* Richard Moore <r_moore at qlc.com>
Gerry_Houlder at notes.seagate.com wrote:
> Unfortunately the "DT for phases" didn't follow that model. It was changed
> to use the new DT DATA phases (same phase as INFORMATION) to make things
> easier for bus analyzers and expanders to interpret things without knowing
> the precise transfer agreement in place for that pair of devices. That kind
> of forced packetized to do DT only so that it followed that convention.

Did it really force this conclusion? If two devices have a negotiated
agreement to do packetized, they will go by the negotiated agreement
regardless of whether MSG is asserted for the information transfer. That
was the argument (as I recall it) that was made when the decision to
define DT Data Phases was made. Also, you have an additional indicator,
namely that devices in a packetized connection go straight to data phase
|from selection whereas devices in a non-packetized connection always go
to message phase first.

> We
> don't really want to add a packetized option to ST DATA phases, do we? That
> probably costs more effort than it is worth.

I don't believe it would take any more effort to do packetized for
ST than for DT. ST/DT affects the front end of SCSI -- generation or
acquisition of data, REQ, and ACK on the bus -- while packetized is more
a back-end function of assembling or interpreting the information. It
might take more effort to design ST out of packetized than to design it

    Richard Moore
    QLogic Corp.
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