Did SCSI-1 have a Recovered Error STATUS?

John Lohmeyer jlohmeye at ncr-mpd.FtCollinsCO.NCR.COM
Wed Feb 16 09:34:49 PST 1994


I'd like to apologize to Jeff about not reading his comment carefully.  He
did indeed mean to say RECOVERED ERROR status code.  I missed the "deep
                                       ^^^^^^^^^^^
dark mists of early SCSI-1" part.  Since I didn't remember this code, I dug 
up my oldest copy of SASI (SASI Rev. C 1/29/82).  Regarding Status bit 0,
it says:

Bit 0    Reserved.  Currently used in some targets for bus parity error.

Also of interest to history buffs:

Bit 7    Extended status.  This bit set means that the second status
         byte is valid.

This was part of a general mechanism to extend status.  The whole status
structure was:

Byte \ Bit 7       6       5        4        3       2       1      0
-----+--------+--------+--------+--------+-------+-------+------+--------+
00   |Ext Stat|Reserved|Reserved|Int Sta | Busy  | Equal | Check|Reserved|
-----+--------+--------+--------+--------+-------+-------+------+--------+
01   |Ext Stat|                   Reserved                      |H.A. Err|
-----+--------+-------------------------------------------------+--------+

We eventually decided that Host Adapter errors were not really part of the 
SCSI status, so we deleted byte 1 (and the implied n more bytes).  Since
bit 7 of byte 0 is still reserved, we could resurrect the extended status
structure, but I sure wouldn't want to be the one to bring that proposal
in front of the committee. :-)

I couldn't find any reference to a recovered error status, however.  My
old SCSI-1 documents are boxed up, so I didn't take the time to dig through
them.  We might have discussed using bit 0 as Jeff suggested, but I don't
recall it ever getting into a draft document.

John

-- 
John Lohmeyer                      E-Mail:  John.Lohmeyer at FtCollinsCO.NCR.COM
NCR Microelectronics                Voice:  719-573-3362
1635 Aeroplaza Dr.                    Fax:  719-597-8225
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