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SAS Interface
68 C141-C013
Each SAS port and expander port shall include an Arbitration Wait Time timer
which counts the time from the moment when the port makes a connection request
until the request is accepted or rejected. The Arbitration Wait Time timer shall
count in microseconds from 0 µs to 32 767 µs and in milliseconds from 32 768 µs
to 32 767 ms + 32 768 µs. The Arbitration Wait Time timer shall stop
incrementing when its value reaches 32 767 ms + 32 768 µs.
SAS ports (i.e., SAS INIT ports and SAS TARG ports) shall start the Arbitration
Wait Time timer when they transmit the first OPEN address frame for the
connection request. When the SAS port retransmits the OPEN address frame (e.g.,
after losing arbitration and handling an inbound OPEN address frame), it shall set
the ARBITRATION WAIT TIME field to the current value of the Arbitration
Wait Time timer.
SAS ports should set the Arbitration Wait Time timer to zero when they transmit
the first OPEN address frame for the connection request. A SAS INIT port or
SAS TARG port may be unfair by setting the ARBITRATION WAIT TIME field
in the OPEN address frame to a higher value than its Arbitration Wait Time timer
indicates. However, unfair SAS ports shall not set the ARBITRATION WAIT
TIME field to a value greater than or equal to 8000h; this limits the amount of
unfairness and helps prevent livelocks.
The expander port that receives an OPEN address frame shall set the Arbitration
Wait Time timer to the value of the incoming ARBITRATION WAIT TIME field
and start the Arbitration Wait Time timer as it arbitrates for internal access to the
outgoing expander port. When the expander device transmits the OPEN address
frame out another expander port, it shall set the outgoing ARBITRATION WAIT
TIME field to the current value of the Arbitration Wait Time timer maintained by
the incoming expander port.
A port shall stop the Arbitration Wait Time timer and set it to zero when it wins
arbitration (i.e., it receives either OPEN_ACCEPT or OPEN_REJECT from the
destination SAS port rather than from an intermediate expander device). If a port
receives a connection request that satisfies its arbitration request (i.e., it receives
an OPEN address frame from the destination SAS port with the INITIATOR
PORT bit set to the opposite value and a matching PROTOCOL field), it shall
stop the Arbitration Wait Time timer unless it accepts the request (i.e., transmits
an OPEN_ACCEPT rather than an OPEN_REJECT).
If two connection requests pass on a physical link, the phy shall determine the
winner by comparing OPEN address frame field contents using the arbitration
priority described in Table 1.26.
Table 1.26 Arbitration priority for OPEN address frames passing on a physical link
Bits 79-64 (79 is MSB) Bits 63-0 (0 is LSB)
ARBITRATION WAIT
TIME field value
SOURCE SAS ADDRESS
field value