Hi,

In the SAS-1.1 spec, it is not very clear if the target device should retry

Sending the SAS_RESPONSE at least one time, if transport layer retries

Are disabled.

For example,

[1] says SSP target port should unconditionally Re-transmit the SAS_RESPONSE

At least one time.

[2] says SSP target port should Re-transmit the SAS-RESPONSE iff transport layer

Retries are enabled.

[3] says transport layer retries only applies to XFR_RDY and DATA frames

On the surface, Re-transmit of SAS_RESPONSE by the target device seems a bit

Dangerous when compared to FCP-1 and FCP-2 based solutions. The SAS initiator port

Is free to immediately re-use the command resources after the SAS_RESPONSE with

Retransmit bit set to 0. If the ACK is lost to the initial SAS_RESPONSE frame (with

Retransmit bit set to 0), then the initiator Port may have trouble the difference between

stale and new command.

Lastly, is there a way to disable all Re-transmit of SAS-RESPONSE at the target device?

==

[1] Taken from SAS-1.1 rev 10 page 364

9.2.4.6 RESPONSE frame - handling of link layer errors

If an SSP target port transmits a RESPONSE frame and receives a NAK for that frame, the SSP target port

retransmits, in the same or a new connection, the RESPONSE frame at least one time with the RETRANSMIT bit

set to one (see 9.2.6.3.3.7.1).

If an SSP target port transmits a RESPONSE frame and does not receive an ACK or NAK for that frame (e.g.,

times out, or the connection is broken):

1) the SSP_TF state machine closes the connection with DONE (ACK/NAK TIMEOUT) (see 7.16.8.6.5);

and

2) the SSP target port retransmits, in a new connection, the RESPONSE frame with the RETRANSMIT bit

set to one (see 9.2.6.3.3.7.1).

The ST_TTS state machine retransmits each RESPONSE frame that does not receive an ACK at least one

time (see 9.2.6.3.3). The number of times it retransmits each RESPONSE frame is vendor-specific.

If an SSP initiator port receives a RESPONSE frame with a RETRANSMIT bit set to one, and it has previously

received a RESPONSE frame for the same I_T_L_Q nexus, the ST_IFR state machine discards the extra

RESPONSE frame (see 9.2.6.3.2). If the ST_IFR state machine has not previously received a RESPONSE

frame for the I_T_L_Q nexus, then it considers the RESPONSE frame to be the valid RESPONSE frame.

[2] Taken from SAS-1.1 rev 10 page 391.

If transport layer retries are enabled, the Transmit Frame request was for a RESPONSE frame, the

vendor-specific number of retries has not been reached, and this state receives one of the following

confirmations:

a) Transmission Status (NAK Received);

b) Transmission Status (ACK/NAK Timeout); or

c) Transmission Status (Connection Lost Without ACK/NAK),

then this state shall:

a) set the RETRANSMIT bit to one; and

b) resend a Transmit Frame (Interlocked) request to the port layer for the failed RESPONSE frame.

[3] Taken SAS-1.1 rev10 page 428

Transport Layer Retries is defined in the Protocol-Specific

Logical Unit mode page for SAS SP (Page Code = 18h).

A TRANSPORT LAYER RETRIES bit set to one specifies that the target port shall support transport layer retries for

XFER_RDY and DATA frames for the logical unit as described in 9.2.4 (i.e., transport layer retries are

enabled). A TRANSPORT LAYER RETRIES bit set to zero specifies that transport layer retries shall not be used

(i.e., transport layer retries are disabled)

Do you think this is an oversight and should include RESPONSE frames too?