RE: Question about Link Fault Signalling
Shimon submitted a comment proposing changing the entry to link down (eitner
RF or LF) from 3 to 4 status messages, with exit on 8 consecutive idle
bytes. While I am open to discussion on the numbers, I think his proposed
text with improved description of the protocol is a great starting point for
discussion. Since this has come up again, here is a slightly edited version
of his proposed text.
"46.2.6 Link fault signaling
"Two link fault conditions are specified for 10Gb/s operation: Local Fault
and Remote Fault. The Local Fault condition at the Reconciliation Sublayer
indicates that a link failure has been detected on the receive path by a
local DTE sublayer. The source of the failure could be at the remote
transmitter, the interconnect between the two DTEs, at one of the local
DTE's devices or the interconnect between the local DTE's devices. The
Remote Fault condition is generated by the Reconciliation Sublayer, and when
received by at a Reconciliation sublayer indicates that a link failure has
been detected by the remote DTE. The source of the failure could be at the
local transmitter, the interconnect between the two DTEs, at one of the
remote DTE's devices or the interconnect between the remote DTE's devices.
" Fault conditions are conveyed over the XGMII using status messages. All
status messages are four bytes in length, and are sent on a single XGMII
clock edge. A status message is indicated by a Pulse control character
aligned to lane 0, with the status condition encoded in the three data bytes
of lanes 1, 2 and 3. The status encodings are shown in Table 46-4."
<Table 46-4>
<For the sake of completeness, also show Lane 0 encoding>
"A PHY indicates Local Fault conditions to the Reconciliation sublayer by
alternating the corresponding status message with Idle control characters on
RXC<3:0> and RXD<31:0>. The Reconciliation sublayer sends the Remote Fault
indication to the remote DTE by alternating the Remote Fault message with
Idle control characters on TXC<3:0> and TXD<31:0>.
"The PHY repeats a Remote Fault indication received from the remote DTE
unless a Local Fault condition is detected resulting in the PHY over writing
the received data with the Local Fault indication.
"The Reconciliation sublayer continuously monitors RXC<3:0> and RXD<31:0>
for status messages. The reception of four status messages of the same type
shall indicate that the corresponding fault condition has occurred. The
reception of four Idle control characters on successive RX_CLK edges (eight
consecutive Idle control characters) shall clear all fault conditions.
" Upon detection of a Local Fault condition, the Reconciliation sublayer
shall:
1) Set the link_fail status indication.
2) Inhibit the transmission of MAC frames.
3) Continuously send alternating Remote Fault messages and Idle control
characters.
"Upon detection of a Remote Fault condition, the Reconciliation sublayer
shall:
1) Set the link_fail status indication.
2) Inhibit the transmission of MAC frames.
3) Continuously send Idle characters.
"After detecting that the Fault condition has cleared (both Local and
Remote), the Reconciliation sublayer shall:
1) Clear the link_fail status indication.
2) Enable the transmission of MAC frames."
--Bob Grow
-----Original Message-----
From: David Gross [mailto:dgross@xxxxxxxxxxxxxxxxxx]
Sent: Wednesday, January 03, 2001 8:48 AM
To: rtaborek@xxxxxxxxxxxxx
Cc: HSSG
Subject: Re: Question about Link Fault Signalling
Hi Rich,
I have a quick question about Remote Fault I was hoping you could
answer. In 46.2.6, it says:"Reception of multiple local fault messages
causes the Reconcilliation Sublayer to inhibit the transmission of
frames by MAC, and to encode remote fault status messages on TXC<3:0>
and TXD<31:0>" It goes on to specify that reception of three LF messages
sets link_fail to 1, and none n 6 clock periods clears link_fail.
My question is this: I believe we said that upon recieving RF, the RS
will output an IDLE stream until it no longer recieves RF. If this is
so, how many RF messages set this condition to be true, and in how many
clocks do we say that this condition is cleared if no RFs are detected.
Is it similar to LF, or do we only require that one RF be detected (and
then for how long before we reset this IDLE output condition of the RS
Tx?)
Thanks in advance.
-Dave Gross