OPC parameters

Dimiter Popoff tgi_earth at yahoo.com
Mon Jan 30 19:22:22 PST 2006

* From the T10 Reflector (t10 at t10.org), posted by:
* Dimiter Popoff <tgi_earth at yahoo.com>
I am trying to figure out how to discover which write
speeds are to be used on a given disk.
I read MMC5 and it does a great job (I am almost
finished now), here goes my question.
 With a new disk just inserted there are no OPC
in the data returned by the READ DISC INFORMATION
After I issue a SEND OPC INFORMATION with no data (0
length) and the DoOpc bit set to 1, the drive does
some work
and next READ DISC INFORMATION returns some OPC data
which look good (sligthly different for different
disks etc.).
However, there is only a single OPC descriptor there;
whereas using the GET PERFORMANCE command with a 3
(i.e. OPC info requested), I get are a number write
different on different disks (media).
 How do I find out which speeds to send with an SEND
INFORMATION command in order to selece and calibrate
one of the speeds the disk is meant to? GET
will do the job, but it is mandatory only for
 devices, presumably it might not be there on some
(not a
big issue for me, I have - alas - no large volumes,
I am trying to do the right thing if the extra cost
not be too high).
Just sending all thinkable speeds with DoOpc? I have
tried that out still but it will likely waste too much
time - I am not sure the drive will know which speeds
make sense to work on at all and which not, what if it
decides to blindly do all - most of them probably 
inapplicable - speed calibrations.

 Thanks in advance. I realise the answer is probably
in the MMC5, but well, it has become pretty bulky
over the years and I would welcome some help, I
I ask the obvious to at least some of you.
 And I guess here is the right place to thank the
for making the documents good as they are.


Dimiter Popoff               Transgalactic Instruments


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