Re: Quantum Fireball with Ramfast

[nparker@cie-2.uoregon.edu (Neil Parker)]

In article <1995Nov5.201009.6826@freenet.victoria.bc.ca>
toh@freenet.Victoria.BC.CA (Marc Sira) writes:
>In our last episode, dempson@atlantis.actrix.gen.nz (David Empson) said:
>
>>"Reselection" is a feature of both SCSI-1 and SCSI-2.  It is not
>>supported by the RamFast, since the RamFast doesn't support the
>>arbitration phase, and has no SCSI ID of its own.
>>
>>The Apple High-Speed SCSI card definitely supports this, and the
>>original Apple SCSI card should do so.
>>
>>If reselection is enabled, the drive will disconnect from the host
>>while a command is being actioned.  When the command is complete (e.g.
>>a READ command is ready to transfer data) the drive will "reselect"
>>the host (i.e. wait for the bus to be free and try to connect to the
>>host, which involves sending the SCSI ID of the host) and transfer the
>>data.
>
>Interesting. Is it possible, then, to convince the drive not to do this?
>
>If not, it sounds as if these drives may not be usable with the RF even
>with a future ROM version. Is this correct?

Yes, the feature can be disabled.  In fact, the feature is supposed to be
off by default, and a SCSI host must make a special effort to tell a device
to turn reselection on.  (It's done during the initial SCSI "message out"
phase, by turning on a flag bit in the "identify" message.)

               - Neil Parker
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