BUFE Bit

KHATTORI KHattori at gnm.infopd.sanyo.co.jp
Wed Feb 28 22:48:25 PST 2001


* From the T10 Reflector (t10 at t10.org), posted by:
* KHATTORI <KHattori at gnm.infopd.sanyo.co.jp>
*
Hello Bill,
I am Katsuki Hattori from SANYO Electric Co.,Ltd..
(And OSJ-EWG Member) 
 
I tell you of the general will of the OSJ-EWG member.
(EWG Meeting: February 27 Tokyo Time)

OSJ was discussed again about BUFE/BUF-Bit.
We (OSJ Members) request you to confirm our proposal as a MMC-3 standard.
 
I have a proposal about the description of BUFE-Bit (ModePage05h).
A sentence to explain about the value of BUFE isn't completed by the MMC-3 document (Rev08).
   Please, See Page158 5.5.4.
   The default value for BUFE shall for CD-R/RW logical units. <- Un-completion.
 
You must see to ModePage2Ah to control BUFE-Bit.
   First, see to BUF-Bit of ModePage2Ah.
   If 1 can be acquired from BUF-Bit(ModePage2Ah), it is possible that BUFE-Bit (ModePage05h) is used.
 
The manufacturer which uses BUFE is to decide the Default value of BUFE.
However, the meaning which "0 and 1" have prescribes it.
  BUFE-bit=0 : indicates that Buffer Under-run Free recording is Disabled.
  BUFE-bit=1 : indicates that Buffer Under-run Free recording is Enabled.
   
--------------------------------------------------------------------
I read your past Mail again.
I could understand the point which you pointed out.
 You suggest an influence on the user who uses old Software.
 ->Old software doesn't know BUFE.
     Therefore, a BUF record isn't given to the user.
I think that it is natural that you are apprehensive.
  
However, the anxiety is unnecessary.
The drive which has a BUF record function is a very new model.
Most Software checks VenderID/ProductID.
Then, the drive which isn't known doesn't do even a connection as a record machine.
Therefore, a problem doesn't seem to happen with the old software and the combination of the BUF drive.
 
You said "A drive should carry out a BUF record automatically.".
However, a new problem occurs in CD-R/RW.
Much software uses READ_BUFFER_CAPACITY_Command.
Some software does characteristic management.
This software is judged "BURError" when data inside Buffer become less than a certain levels.
In this case, the "drive of carrying out a BUF record" doesn't return an error status to the host.
Both (host and drive) wait for a partner response.
I actually saw this symptom in the experiment.
Therefore, a CD-R/RW drive shouldn't carry out a BUF record automatically.
 
Regards,
Katsuki  

-----Original Message-----
From: Bmcferrin at aol.com [mailto:Bmcferrin at aol.com]
Sent: Monday, February 19, 2001 12:40 AM
To: mtfuji5 at avc-pioneer.com; mmc at dt.wdc.com
Subject: Re: BUFE Bit


Murata-san, 
You have listed my primary concern here: 




3. As a default, BUFE is off. It means that if application software need to 
set BUFE, 
  they must set the BUFE bit. 



If BUFE is switched off by default AND the host software has no knowledge of 
BUFE and its use, then our user is not allowed to benefit from buffer 
underrun free operation because we have declared that it must be switched off 
by default. 

Consider this very common example: 
There are drives shipping today which provide buffer underrun free operation 
without the use of BUFE.  A CD-RW drive user talks to a friend who has bought 
one of those drives and his friend tells him that it is wonderful.  This user 
now buys a new drive because the box advertises that he gets new high speed 
recording with buffer underrun free operation.  BUT, it is "too new" - it 
knows about BUFE and uses BUFE.  The user does not get buffer underrun free 
operation because his installed software does not know about BUFE and 
therefore does not switch on BUFE.  This user is unhappy and returns the 
drive for a refund.  He then says bad things about the maker of the drive.   
Do we want this? 

Now, let me stress that I very much want to keep the BUF bit in Mode Page 2Ah 
and in the two feature descriptors as described by OSJ.  This allows newer 
software to be aware of the drive capability.  Some burner software uses 
large host-based buffer expansion and task priority overrides as mechanisms 
to protect from potential buffer underruns.  If the host software is aware of 
the  new drive capability, then it can free these resources, making the host 
computer run more smoothly. 

Bill McFerrin 


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