SAS-2 rev.15 Missing Sync lost message definition

Samek samek at halstor.com
Sat Dec 6 10:05:07 PST 2008


* 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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