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SAS Interface
54 C141-C013
1.4.4 Primitives used only inside SSP and SMP connections
1.4.4.1 ACK (acknowledge)
The ACK primitive indicates that an SSP frame is received normally. When a
drive receives an SSP frame, and the CRC field in the received SSP frame is
correct, the drive sends the ACK primitive within 1 ms.
1.4.4.2 CREDIT_BLOCKED
The CREDIT_BLOCKED primitive indicates that no more credits can be sent
during this connection. When a drive determines that it can give out no more
credits during the connection, the drive sends the CREDIT_BLOCKED primitive
to avoid credit timeout. A drive sends the CREDIT_BLOCKED primitive in any
of the following cases:
1) When the drive sends an OPEN frame and, then, receives the OPEN_ACCEPT
primitive from the initiator during the abort processing in the drive, the drive
sends the CREDIT_BLOCKED primitive instead of an RRDY primitive.
2) When the drive determines during the connection that it has entered a
condition where abort processing inside the drive is necessary, if an SSP
frame is received from the initiator, the drive sends the CREDIT_BLOCKED
primitive instead of an RRDY primitive.
After sending the CREDIT_BLOCKED primitive, the drive must wait until the
connection is closed before it can send an RRDY primitive.
Meanwhile, when a drive receives the CREDIT_BLOCKED primitive from the
initiator, the drive performs any of the following processing:
1) At the time of the receipt of the CREDIT_BLOCKED primitive, if the drive
holds credits that have been given before and has frames to send, the drive
can send as many frames as there are credits being held at this time.
2) At the time of the receipt of the CREDIT_BLOCKED primitive, if the drive holds
credits that have been given before but has no frames to send, the drive sends the
DONE (CREDIT TIMEOUT) primitive and starts the close processing.
3) At the time of the receipt of the CREDIT_BLOCKED primitive, if the drive
holds no credits, it sends the DONE (CREDIT TIMEOUT) primitive and
starts the close processing.
1.4.4.3 DONE
A DONE primitive indicates the start of the close processing of an SSP
connection. In the close processing, in principle, when no frame for processing
remains on the side of the OPEN frame sender (recipient of the OPEN_ACCEPT
primitive), a DONE primitive is sent. However, there is no rule concerning which
side should first start the close processing.
Table 1.15 contains DONE primitive definitions.