SCSI-3 Download Code
Gerry Houlder
Gerry_Houlder at notes.seagate.com
Sun Sep 6 23:24:59 PDT 2015
_Date: 01-19-94 10:15:34 AM
_To: scsireflector
_Recipient: scsi at WichitaKS.NCR.COM@internet
_From: Gerry Houlder at SEAGATE
_Subject: re: SCSI-3 Download Code
In our Elite product, we added the abilty to download the code in 32K byte
chunks (we needed 5). We used the regular WRITE BUFFER command, Download & Save
mode, and buffer IDs 0 thru 4. Each chunk had to be exactly 32K bytes or we
rejected the command with ILLEGAL REQUEST (exception: buffer ID 0 could also be
used to download the entire 160K bytes in one command if the transfer length
said 160K bytes).
Our implementation required the download to start with buffer ID 0 and end with
buffer ID 4. It turns out that the order of the other buffer IDs could be
changed without any ill effects. When a WRITE BUFFER to buffer ID 4 occurred,
it checked to make sure that data from buffer IDs 0 through 3 had already been
received (and stored away earlier) and all 5 parts are checksummed before the
drive will respond with GOOD status. The earlier WRITE BUFFER commands can end
with GOOD status even illegal data was sent. This is because our checksum
boundaries are not on the 32K boundaries, so all parts must be present before
we can be sure that the checksum operation will succeed.
Things like SCSI reset before the last WRITE BUFFER causes the entire operation
to be lost, so it must be restarted. There are a few other operations we had to
watch out for, but the response to a reset shows the general recovery
philosophy we used.
I hope Jim Mcgrath's proposal allows for this operation. There really wasn't
anything special we had to add to achieve this capability.
--
Gerry Houlder (Gerry_Houlder at notes.seagate.com)
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