Credit Timeout with ACK/NAK not balanced

George Penokie gop at us.ibm.com
Wed Nov 13 09:23:31 PST 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* George Penokie <gop at us.ibm.com>
*




In the current SAS SSP_TF2:Tx_Wait state it states that if the credit
timeout timer expires a transition is made to the Indicate_Done_Tx state.
There is no qualification that ACK/NAK have to be in balance before the
transition is made. Although this works, in that it causes no dead-locks,
invalid data, nor any confusion on the two sides of the bus it could cause
a command to be aborted when not necessary.

I suggest qualifying the transition such that it is not made unless there
is ACK/NAK Balance or there is an ACK/NAK timeout.

The requirement would read something like this:

If the Credit timeout timer expires before the Tx Credit Status (Available)
parameter is received and the last Tx Balanced Status parameter received
had an argument of Balanced this transition shall pass a Credit Timeout
argument to the Indicate_Done_Tx state.  If the last Tx Balanced Status
parameter received had an argument of Not Balanced then this transition
shall occur after a Tx Balanced Status (Balance) parameter is received or
after an ACK/NAK Timeout parameter is received. If a Tx Balanced Status
(Balanced) parameter was received this transition shall pass a Credit
Timeout argument to the Indicate_Done_Tx state. If an ACK/NAK Timeout
parameter was received this transition shall pass an ACK/NAK Timeout
argument to the Indicate_Done_Tx state.

I believe this change is technical (unless this is the way it was supposed
to be) and therefore would have to be a letter ballot comment. But I wanted
to let you know about this and see if there was any comments on it.

Bye for now,
George Penokie

Dept 2C6  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208   FAX: 507-253-2880


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