Re: [Linuxptp-users] PTP_TIMESCALE flag query

[Richard C. <ric...@gm...>]

On Wed, Mar 30, 2016 at 07:05:00AM +0000, Ledda William EXT wrote:
> Because It is implemented according to the IEEE 1588 standard. It is
> the GMC that set this bit in the ANNOUNCE message. This information
> is then available through the Time Properties Data Set of the
> clock. The question is... why do you need it also for Sync and
> Follow Up messages?

Yes, for 1588, that bit is only set for Announce messages.
For AVB, the bit is supposed to be ignored by the receivers.

                    Table 10-6 - Values of flag bits

  Octet  Bit  Message Types   Name          Value
  1      3    All             ptpTimescale  Reserved as TRUE,
                                            ignored on reception

                                    - IEEE 802.1AS-2011, page 89

Since the bit must be ignored, we simply send according to 1588,
knowing that any correct AVB implementation must ignore the bit.

The statement "Reserved as TRUE" is quite strange.  Normally, reserved
bits are sent on the wire cleared.  I understand this statement to
mean, that the *logical* value for AVB is always TRUE, even though the
on the wire value may be zero.  Otherwise, the restriction "ignored on
reception" does not make any sense.

Thanks,
Richard