SAS-2 rev.15 Missing Sync lost message definition

Day, Brian Brian.Day at lsi.com
Sun Dec 7 18:04:32 PST 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* "Day, Brian" <Brian.Day at lsi.com>
*
Hello Samek...
I'm not sure I agree with SAS being specified with too infrequent primitives
relative to loss of sync.
SAS 2 defines an ALIGN primitive to be sent every 3.4 us (approximately... it
is every 128 dwords at 1.5Gbps).
The DWS Reset Timeout is specified as 1 ms.
So assuming link multiplexxing is not enabled, from the loss of sync
(regardless of how often this may occur due a particular system's BER), there
are almost 300	ALIGNs permitting a device to recover sync during the DWS
Reset Timeout period before it gives up and performs the link reset.
Brian Day
LSI Corporation
-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Samek
Sent: Saturday, December 06, 2008 11:05 AM
To: Elliott, Robert (Server Storage); t10 at t10.org
Subject: Re: SAS-2 rev.15 Missing Sync lost message definition
* From the T10 Reflector (t10 at t10.org), posted by:
* "Samek" <samek at halstor.com>
*
In a real life, due to various factors, the loss of sync will be a common
occurence and due to the infriquent primitives may cause link resets, which
in SAS/SATA cases are really bad. By the way, dword synchronization may
happen any time, not only during a speed negotiations.
Samek Mokryn
President
HalStor Inc.
www.halstor.com
----- Original Message -----
From: "Elliott, Robert (Server Storage)" <Elliott at hp.com>
To: <t10 at t10.org>
Sent: Wednesday, December 03, 2008 2:30 PM
Subject: RE: SAS-2 rev.15 Missing Sync lost message definition
>* From the T10 Reflector (t10 at t10.org), posted by:
> * "Elliott, Robert (Server Storage)" <Elliott at hp.com>
> *
> DWS Lost is the name of a message going to SP, not the SP receiver.
> They're sent at similar times and possibly could be made identical.
>
> Although the SAS standard (like most other serial protocols) only
> requires a BER of 10^12 (which is one error every 2.77 min per one
> direction of a physical link at 6 Gbps), a system generating anywhere
> near those number of errors will have so many other problems it won't
> be viable.  Dword synchronization mainly just happens once during
> speed negotiation. Most of the time is spent finding the center of the
> bits; once done, identifying the dword boundary by finding a comma is easy.
>
>
>
> -----Original Message-----
> From: Samek [mailto:samek at halstor.com]
> Sent: Tuesday, December 02, 2008 6:13 PM
> To: Elliott, Robert (Server Storage); t10 at t10.org
> Subject: Re: SAS-2 rev.15 Missing Sync lost message definition
>
> It looks to me that the DWS Lost message does the same job. I can
> hardly see why there is a need for two.
> These are however minor problems. I have much bigger problem with the
> fact that the comma characters are so sparse in the SAS protocol,
> resulting in a longer time to acquire synchronization, specially in
> the noisy environment (please note that with a lower bit energy in
> faster rates the SNR drops dramatically), which may lead to link
> resets - catastrophic from the performance point of view.
>
> Samek Mokryn
> President
> HalStor Inc.
> www.halstor.com
>
>
>
> ----- Original Message -----
> From: "Elliott, Robert (Server Storage)" <Elliott at hp.com>
> To: <t10 at t10.org>
> Sent: Tuesday, December 02, 2008 11:17 AM
> Subject: RE: SAS-2 rev.15 Missing Sync lost message definition
>
>
>>* From the T10 Reflector (t10 at t10.org), posted by:
>> * "Elliott, Robert (Server Storage)" <Elliott at hp.com>
>> *
>> The SP receiver detects ALIGNs, TRAIN_DONEs, and Dwords and sends
>>them as  ALIGN Received, TRAIN_DONE Received, and Dword Received
>>messages.  See  figure 35 on page 72.
>>
>> If dword synchronization has been lost, however, it stops sending
>> those messages.  SP_DWS tells the SP receiver that dword
>> synchronization has been lost using the Sync Lost message.  See this
wording on page 285:
>>
>> "The ALIGN Received, Dword Received, and TRAIN_DONE Received messages
>> are only sent after the SP_DWS state machine has achieved dword
>> synchronization."
>>
>> ________________________________
>>
>> From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Samek
>> Sent: Thursday, November 27, 2008 1:46 PM
>> To: t10 at t10.org
>> Subject: SAS-2 rev.15 Missing Sync lost message definition
>>
>>
>> SP_DWS (6.9) defines a Sync Lost message sent by the SP_DWS state
>> machine to the SP receiver, however there is no definition anywhere
>> what the SP receiver should do with this message. Any suggestions?
>>
>> Happy Thanksgiving
>>
>> Samek Mokryn
>> President
>> Halstor Inc.
>> www.halstor.com
>>
>> *
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>
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