SEND_OPC command with DO_OPC=1 -- questions and comments

Henry Gabryjelski Henry.Gabryjelski at microsoft.com
Fri Apr 28 08:17:28 PDT 2006


* From the T10 Reflector (t10 at t10.org), posted by:
* "Henry Gabryjelski" <Henry.Gabryjelski at microsoft.com>
*
On many current drives, we are seeing quick exhaustion of OPC area.  So,
I would like to highlight a few lines of the specification, and ask
firmware implementors' opinion on implementation.
>From SEND_OPC command, Fuji 6:
The DoOpc bit, when set to one, indicates the logical unit shall perform
an OPC operation to set the OPC values for the current speed.
>From the Mt. Fuji text, it states that an OPC operation must be
performed.  However, the definition of the OPC operation that must be
performed is not clarified.  I believe that an OPC operation is best
defined as the drive determining the OPC settings for the current media
and write speed combination.  So, if a drive already knows the OPC for
the current write speed (for example, by reading OPC information already
written to the media by itself), no use of the OPC area is necessary.
>From SEND_OPC command, MMC 5r02:
If DoOpc is set to one, the Drive shall determine OPC values for the
current recording conditions. It may be necessary to perform an OPC
operation. These OPC values shall become current. When DoOpc is set to
one,
the Parameter List Length field is ignored.
>From the MMC text, this definition more closes matches what I understand
to be an intended behavior.
Q: Is there a technical reason to always use OPC area to find new OPC
values when SEND_OPC with DoOpc=1 is sent to the drive?  I think maybe
it is better to use the MMC defined method, but want to understand if
there are reasons not to implement this way.
Thanks,
.
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