RE: 64B/66B Control Codes Mapping & Bit Order
Ben and Wesley,
In these drawings, I was consistant with 802.3's usual notational
conventions
which show bit fields with the LSB/first transmitted bit on the left. For
instance,
see Figure 3-1. If you search the base standard for LSB, you will find that
almost
all* figures and binary bit representations (see 22.2.3.2.1 for an example)
are
shown with least significant bit on the left while hex representations of
fields
are shown in the normal order. I didn't make it that way but at this point
we
should not change it.
Pat
*The only deviant I found was 23-7 but the code tables for 23 (see Annex
23A)
follow the convention.
-----Original Message-----
From: Wesley Lee [mailto:wlee@xxxxxxxxxx]
Sent: Monday, October 09, 2000 12:33 PM
To: stds-802-3-hssg@xxxxxxxx; bbrown@xxxxxxxx
Subject: Re: 64B/66B Control Codes Mapping & Bit Order
Ben,
I'd support you in recommending to flip the order of bits in Fig 49-5 as
you suggest in the following. Table 49-1 shows bits msb->lsb
but fig 49-5 shows the opposite so one can't simply stuff the
control codes in table 49-1 into fig 49-5.
Regards,
-Wesley Lee
ben brown wrote:
[snip]
Hope this helps. Although it might be too late to make
a dramatic change to this table at this point (simply
because people are beginning to be familiar with it),
I would be eager to recommend to the clause editor that
this table be redrawn where the first column changes the
order of the bytes from D0...D7 to D7...D0. Then, move
the SYNC column to the far left and reverse the order of
those bits (DATA = 10, CONTROL = 01). The Block Payload
column could then be re-ordered to show D7...D0 for the
Data Block Format and C7...C0, Type Field for Control
Block Format. This way, the 66-bit field is laid out
in front of you with [65] (the msb) on the left and [0]
(the lsb) on the right, the way many of us are most
familiar with looking at numbers or fields. Also, the
hexadecimal equivalents of fields, which are written with
msn (most significant nibble) on the left and lsn on
the right, could be simply expanded into their binary
equivalents without having to perform a mental bit swap
to match the table.
--
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