About CD-ROM READ(10) Command

Rob Sims robsims at hootie.lvld.hp.com
Fri Apr 17 16:35:59 PDT 1998


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* "Rob Sims" <robsims at hootie.lvld.hp.com>
*
> * From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
> * Gene_Milligan at notes.seagate.com
> *
> I am forwarding your memo below to the T10 reflector since T10 is the SCSI
> committee that deals with Multi Media Command sets (MMC) and (MMC-2).

> "Yukihiko Okada" <okada.yukihiko at z-prj.kenwood.co.jp> on 04/16/98 07:39:40
> PM

>   Dear Sir,
>                  About CD-ROM READ(10) command
> 
>   We are designing CD-ROM drive now.
> We have a question about READ(10) command "Transfer Length=0"
> in page 137 of "ATA Packet Interface for CD-ROMs SFF-8020i".
>   This command has foot notes as "A transfer length of zero
> indicates that no logical blocks shall be transferred."
>   Could you advice us that which interpretation is right about
> this command, (a) or (b) ?
> 
> 
>       (a) Even if transfer length=0, seek to Logical Block Address
>            and buffering to drive RAM from medium, then finish.

>       (b) Because of transfer length=0, NO seek operation, and
>            NO buffering from medium, then finish.

The drive can do what it wants.  The command should not return an 
error in either case.  For example, if the LBA is not readable, this 
does not cause an error because no data was requested from that 
block.

It's even questionable if an error should be generated if the LBA is 
outside of the range of the medium.  For a Play Audio command of zero 
length, the command shall succeed no matter what the requested 
address is.

This is a case where the manufacturer should examine where such a 
command might be used, and determine from that what results in the 
most reliable, fastest, or easiest implementation.
-- 
Rob
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