less than whole lengths

Pat LaVarre LAVARRE at iomega.com
Wed Mar 13 13:30:00 PST 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Pat LaVarre" <LAVARRE at iomega.com>
*
This doesn't yet preclude copying in x24 bytes of op x12 Inquiry data, does
it?

This just says the block size for block data out now has to be a multiple of
8, precluding, for example the x 914 91C 924 (aka 2324, 2332, 2340) that
rumour says some SFF-8090 folk like?

Or does this also tell us that, say, ModeSelect data copied out has to have a
length that is a multiple of 8?

Sorry I'm so clueless re FC-PLDA, thanks again in advance.



x4402 Pat LaVarre   p.lavarre at ieee.org
http://members.aol.com/plscsi/


>>> Robert Snively 03/13/02 02:20PM >>>
Already done.

See  FC-PLDA, clause 8.2.2

 The DATA_RO parameter in the FCP_XFER_RDY IU on 
 write type operations for disk devices shall
 be a multiple of 8 bytes.

Bob



>>> ...

> 512 2048 2056 2324 2332 2336 2340 2352 2368 2448

Ouch.  For these 10 block sizes I think I see the GCD (greatest common
divisor) is 4.  If we say 8 we lose 2324, 2332, 2340.  If we say x10 we also
lose 2056.  Ouch.

x200 = 512 = 1 * 2**9
x800 = 2048 = 1 * 2**11
x808 = 2056 = 1 * 2**3 * 257
x914 = 2324 = 1 * 2**2 * 7 * 83
x91C = 2332 = 1 * 2**2 * 11 * 53
x920 = 2336 = 1 * 2**5 * 73
x924 = 2340 = 1 * 2**2 * 3**2 * 5 * 13
x930 = 2352 = 1 * 2**4 * 3 * 49
x940 = 2368 = 1 * 2**6 * 37
x990 = 2448 = 1 * 2**4 * 3**2 * 17

...

SFF-8090 says:

If supported, block sizes (see See  Block Descriptor Block Sizes for Read  on
page 234.) shall include 2048 and may include 512, 2056, 2324, 2332, 2336,
2340, 2352, 2368, and 2448 bytes. The Table of Block Sizes for Read shows the
implementation of the various block sizes.

Table 158 - Block Descriptor Block Sizes for Read

Size Readable block types
512 Mode 1 or Mode 2 Form 1 sectors divided into four blocks each.

2048 Mode 1, Mode 2 Form 1, or DVD

2056 Mode 2 Form 1 with subheader. Equivalent to Read CD, Flag = 50h.

2324 Mode 2 Form 2 with no subheader. Note: There is no mapping to Read CD, as
the 4 spare bytes are not returned.

2332 Mode 2, form 1 or 2 data. The drive shall operate as specified for 2048
byte blocks except: Both forms send 2332 byte blocks. Form 1 blocks return the
third layer ECC with the user data. Note: There is no mapping to Read CD, as
the 4 spare bytes are not returned.

2336 Mode 2 data The drive shall operate as specified for 2048 byte blocks
lengths. This mode will include all data, including Yellow Book Mode 2 sectors
and Form 1 and Form 2. Equivalent to Read CD, Flag = 58h.

2340 All bytes except the synchronization field. Equivalent to Read CD, Flag =
78h.

2352 Audio or raw blocks. The drive shall operate as specified for 2048 byte
blocks. Reads of data mode sectors shall return descrambled data. Equivalent
to Read CD, Flag = F8h.

2448 or 2368 Audio or raw blocks with raw sub-channel. The drive shall not
perform the data descrambling operation. Equivalent to Read CD, Flag = F8,
Sub-channel data selection = 010b (2448) or Sub-channel data selection = 001b
(2368).

...



> -----Original Message-----
> From: Pat LaVarre [mailto:LAVARRE at iomega.com] 
> Sent: Thursday, March 07, 2002 5:03 PM
> To: t10 at t10.org 
...
> >  It is just unfortunate (and a historical accident)
> > that standard ... data is ... is not 32-bit aligned.
> 
> A accident nowadays looming larger is that so much standard 
> data is not 64-bit (8 byte) aligned e.g. the x24 bytes
> commonly moved in by the cdb x 12 0 0 0 24 0
> i.e. Inquiry for up to x24 bytes.
> 
> It will be fun to see if the people who have so successfully 
> resisted moving anything but N * 4 bytes will soon try
> to move nothing but N * 8 bytes.
> 
> Often I've wished there was a way to be a Scsi device yet 
> still insist on never moving anything but N * K bytes,
> where K was my block size, like Ata does.
> 
> Pat LaVarre

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