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SAS Interface
66 C141-C013
1.5.5 Connections
1.5.5.1 Connections overview
A connection is opened between a SAS INIT port and a SAS TARG port before
communication begins. A connection is established between one SAS INIT phy
in the SAS INIT port and one SAS TARG phy in the SAS TARG port.
SSP INIT ports open SSP connections to transmit SCSI commands, task
management functions, or transfer data. SSP TARG ports open SSP connections
to transfer data or transmit status.
Also at the SSP TARG port, an SSP connection must be established before data or
a status is sent.
The OPEN address frame is used to request that a connection be opened. AIP,
OPEN_ACCEPT and OPEN_REJECT are the responses to an OPEN address
frame. BREAK is used to abort connection requests and to unilaterally break a
connection. CLOSE is used for orderly closing a connection.
Connections use a single pathway from the SAS INIT phy to the SAS TARG phy.
While a connection is open, only one pathway shall be used for that connection.
A wide port may have separate connections on each of its phys.
1.5.5.2 Connection request
The OPEN address frame is used to open a connection from a source port to a
destination port using one source phy and one destination phy.
To make a connection request, the source port shall transmit an OPEN address
frame through an available phy. The source phy shall transmit idle dwords after
the OPEN address frame until it receives a response or aborts the connection
request with BREAK.
After transmitting an OPEN address frame, the source phy shall initialize and start
a 1 ms Open Timeout timer. Whenever an AIP is received, the source phy shall
reinitialize and restart the Open Timeout timer. Source phys are not required to
enforce a limit on the number of AIPs received before aborting the connection
request. When any connection response is received, the source phy shall
reinitialize the Open Timeout timer. If the Open Timeout timer expires before a
connection response is received, the source phy may assume the destination port
does not exist and shall transmit BREAK to abort the connection request.
The OPEN address frame flows through expander devices onto intermediate
physical links. If an expander device on the pathway is unable to forward the
connect request because none of the prospective physical links support the
requested connection rate, the expander device shall return OPEN_REJECT
(CONNECTION RATE NOT SUPPORTED). If the OPEN address frame reaches
the destination, it shall return either OPEN_ACCEPT or OPEN_REJECT.
Rate matching shall be used on any physical links in the pathway with negotiated
physical link rates that are faster than the requested connection rate.