SPC Inquiry for Quad-Aligned Zero -- deprecated since SPC-4 maybe

plavarre at lexar.com plavarre at lexar.com
Thu Jan 3 15:44:23 PST 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* <plavarre at lexar.com>
*
Gerry,
I see you proposing this change:
"""The ALLOCATION LENGTH field is defined in 4.3.4.6. [+ An allocation
length of zero specifies that no data shall be transferred. This
condition shall not be considered as an error.] If EVPD is set to zero,
the allocation length should be at least five, so that the ADDITIONAL
LENGTH field in the parameter data (see 6.4.2) is returned. If EVPD is
set to one, the allocation length should be should be at least four, so
that the PAGE LENGTH field in the parameter data (see 7.6) is
returned."""
I agree inserting those shall redundancies at that point would improve
the clarity of our problematic shall text ... but I think that specific
proposal affects only the unclear shall's without actually correcting
our broken should's.
I think the change that's more worthwhile is fixing the broken should's.
Personally I don't mind if we ever bother clarifying the problematic
shall's or not.
The broken should's I see are like this:
i) """If EVPD is set to zero, the allocation length should be at least
five, ..."""
ii) """If EVPD is set to one, the allocation length should be ... at
least four, ..."""
Get it?
My reading of that pair of should's comes out of the context that I
remember that we always set the EVPD bit of the CDB to zero or to one,
because the EVPD is a single real bit of the CDB, and of course all real
bits are only zero or one in any actual instance. Thus any pair of
claims deciding EVPD zero and then also deciding EVPD one implicitly
presents a claim for always.
I therefore see us saying the allocation length should always be at
least four.
That claim is false by overstatement. We actually mean to say the
allocation length should always be at least four when the allocation
length is not zero. For example, we could say:
"""In order to get the information that tells you how many bytes of data
are available the allocation length must be at least this big. If you
don't care about retrieving the Page Length parameter or the Available
Length parameter then you don't have to follow this suggestion."""
All the same, I guess changing over to plain English like that would be
too big of a change. So instead I suggest the small corrections:
"""The ALLOCATION LENGTH field is defined in 4.3.4.6. If EVPD is set to
zero, the allocation length should be [+ zero else should be] at least
five, so that the ADDITIONAL LENGTH field in the parameter data (see
6.4.2) is returned. If EVPD is set to one, the allocation length should
be [+ zero else] should be at least four, so that the PAGE LENGTH field
in the parameter data (see 7.6) is returned."""
That newest change proposal lets us keep all three of the original
should's, but adds a fourth should and a few words to make the whole
thing actually say what we mean.
Like it?
Hope this helps, curiously yours, Pat LaVarre
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