RE: Question about Link Fault Signalling
Yariv,
The clearing of fault should be based on the cessation of fault messages for
a given number of RX_CLK cycles and not on receiving a specific number of
idles. We shouldn't complicate this protocol by requiring a period when
fault conditions have been cleared and frames are still inhibited.
There is no reason that a frame received right after the fault condtions
clear shouldn't be received. There are some things right now, like the
current 10GBASE-X receive state machine that don't work for that, but they
can be fixed.
Regards,
Pat Thaler
-----Original Message-----
From: Yariv Anafi [mailto:yariv@xxxxxxxxxxxxx]
Sent: Thursday, January 04, 2001 12:32 AM
To: Stephen.Finch@xxxxxx
Cc: stds-802-3-hssg@xxxxxxxx
Subject: Re: Question about Link Fault Signalling
Hi all,
There is something missing in your description. At the last stage (7)
MAC1 was transmitting RF
and move to transmit IDLE or packets. At the same time MAC2 is in a state of
detecting RF and will soon see
what MAC1 is sending. We must guarantee that MAC1 will transmit enough
cycles of IDLE before it start to send packets
otherwise MAC2 will not clear the RF state since it do not detect enough
IDLE bytes. Remember that some IDLE column are
lost due to lane alignment.
We need to add that when clearing a fault condition by detecting 8 bytes of
IDLE, one must send at least 12 bytes of IDLE
before clearing the link fail status, and enable the transmit of packets
Stephen.Finch@xxxxxx wrote:
David,
let me take a swing at this ball....
Power up
1. Both sides send idles until idles are received, packets
can be sent only if Idles and/or packets are being received.
|--(Idle)--> PHY |
MAC1 | | MAC2
| PHY <--(Idle)--|
2. Since we're starting up, the links aren't locked yet, so
somewhere in the phy on the receive path in both directions
someone is generating LF. This probably happens in both
directions, so both sides are generating LFs somewhere in the
PHY layer.
|--(Idle)--> PHY ----(LF)-->|
MAC1 | | MAC2
|<--(LF)---- PHY <--(Idle)--|
3. Both MAC/RS's see LF and start send RF (instead of just Idle's). We
stay here until a link comes up.
|----(RF)--> PHY ----(LF)-->|
MAC1 | | MAC2
|<--(LF)---- PHY <--(RF)----|
4. One or the other of the links obtain sync and starts working (you
can work out what happens if both come up simultaneously). We'll assume
its on the top path. When a link comes up, it stops generating LF and
passes through what is being sent, i.e., the RF that is being sent by
the MAC (with RS) in its direction.
|----(RF)--> PHY ----(RF)-->|
MAC1 | | MAC2
|<--(LF)---- PHY <--(RF)----|
5. A MAC2 receives the RFs. This causes MAC2 to stop sending RF and
start sendin Idles. (No packets yet)
|----(RF)--> PHY ----(RF)-->|
MAC1 | | MAC2
|<--(LF)---- PHY <--(Idle)--|
6. When the other link comes up, the PHY element that was generating
LFs stops generating LF and passes through what is being sent, i.e.,
Idles.
|--(RF)----> PHY ----(RF)-->|
MAC1 | | MAC2
|<--(Idle)-- PHY <--(Idle)--|
7. When MAC1 receives Idles (not LF and not RF), it can send packets or
Idles.
|-(Idle/P)-> PHY -(Idle/P)->|
MAC1 | | MAC2
|<--(Idle)-- PHY <--(Idle)--|
8. When MAC2 receives Idles or packets, it too can start sending packets
or continue to send idles.
AND WE'RE UP.
Hope this makes it clear.
Steve Finch
"David Gross" <dgross@xxxxxxxxxxxxxxxxxx> on 01/03/2001 02:35:27 PM
To: "Grow, Bob" <bob.grow@xxxxxxxxx>
cc: rtaborek@xxxxxxxxxxxxx, HSSG <stds-802-3-hssg@xxxxxxxx>
Subject: Re: Question about Link Fault Signalling
Thanks for the response Bob,
I'd just like to make one clarification which I think might be
necessary. I'd like to see "In the case of a Local Fault condition..."
rather than "Upon detection of a Local Fault condition..." (and likewise
for Remote Fault). The reason for this is that since upon start-up, one
can assume that both devices will be in LF and transmitting RF. This
implies that once a device can start recieving data (i.e.: no longer
have a LF) it will be recieving RF. As a result, as the definition seems
to imply, the Fault conditions won't be cleared (The IDLE control words
won't be detected for 2 clock edges), but instead Remote Fault will be
detected. Since RF and LF cannot be detected at the same time (LF
prevents the transmission of recieved RF), it is logical that LF will be
cleared while RF will be achieved. There should be something in there
which allows for the clearing of LF in such a case, and jumping from the
LF condition immediately to the RF condition. Let me know what you
think.
-Dave Gross
Grow, Bob wrote:
>
> 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
<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
--
thanks,
Yariv Anafi
Galileo Technology Ltd.
Moshav Manof, D.N. Misgav 20184
Email - mailto:yariv@xxxxxxxxxxxxx <mailto:yariv@xxxxxxxxxxxxx>
Tel Haifa - + 972 4 8225046 ext. 414
Tel Manof - + 972 4 9999555
FAX - + 972 4 8326420
WEB SITE - http://www.GalileoT.com <http://www.GalileoT.com>