I haven’t seen an update on this proposal, but I did want to see some discussion prior to the T10 week, so here goes.

In SAS-2 today a phy sends only one Identify frame and makes one attempt to receive an Identify.  If the phy receives an SOAF and that address frame is of the wrong length or has incorrect CRC, the reception attempt fails and the exchange of the Identify frame fails.  The phy does not go into normal operation and a phy reset sequence is the only option for recovery.

The goal, as I understand it, is to allow (not require) a phy to send its Identify frame three times and to allow it to discard invalid frames and not treat the detection of an invalid frame as a fatal error.  The reception process would time out if no Identify frame was received before the Receive Identify Timeout timer times out.

The issues, as I see them are:

1.  There is no timing specified as to the repetition of Identify frames.  

The Identify frames could be sent back-to-back, with no intervening idle dwords, or they could be spaced far apart, up to something just short of the Receive Identify Timeout period.  

It appears there are implementations that are not capable of receiving back-to-back frames with no intervening idle dwords.  If a phy with such a receiver were connected to a phy that transmitted the Identify three times in a row without intervening idle dwords, then the goal of this proposal would not be obtained.

I see no advantage to sending the multiple Identifies with “significant” time delay between them.

I would propose that, if a phy transmits three Identifies that a minimum of six idle dwords be transmitted between the Identify frames and no more that 16 idle dwords be transmitted between Identify frames.  (If these numbers aren’t agreeable, let’s find numbers that are.)

2.  If one side transmits the Identify three times and the other side only once, then the side that send only one will enable its higher layer protocol state machines after sending only one.  It is possible (and I can argue probable if the phy reset sequence occurred as a link recovery event) that the phy sending only one Identify could send an Open Address frame before the phy sending three Identify frames has entered normal operation.  This would result in a timeout of an Open request.  Not an unrecoverable event, but still not a desirable event either.  So, should we require all phys to not send an Open Address frame until some time frame after the successful exchange of an Identify?  Like 1 ms?

One last question, should all SAS-2 compliant devices be required to send three Identify frames?

Additional note:  The text and state changes to the IR state machines (3 of them), as they appear in the latest proposal, are not sufficient.  If we can agree to the above issues, then we can work on these issues.

Regards,

Steve Finch

STMicroelectronics