1.6.5.3 Paced Transfer - Fujitsu MAW3073 SERIES Specifications

1.6.5.3 Paced transfer

(1) Paced transfer overview
If a paced transfer agreement has been established it shall be used in DT DATA phase and
information unit transfers shall be used. The transfer agreement also specifies the REQ/ACK offset
and the transfer period.
When paced transfers are being used data shall be transferred using DT data transfers on 16-bit
wide buses that transmit and receive data using LVD transceivers.
If driver precompensation is enabled at the SCSI device, that SCSI device shall apply driver
precompensation to all the data, parity, REQ, and ACK signals.
During paced DT data transfers, if the phase of the P1 signal indicates data is valid (see 1.6.5.3.3)
on REQ or ACK assertions, data shall be clocked by the originating SCSI device by both the
assertion and negation of the REQ or ACK signal lines. The receiving SCSI device shall clock DT
data on both the assertion and negation of the REQ or ACK signal line after having been processed
by the receiving SCSI device. If the phase of the P1 signal indicates data is invalid on REQ or
ACK assertions, data shall not be clocked by the originating SCSI device and shall be ignored by
the receiving SCSI device. If driver precompensation is enabled at the originating SCSI device, the
originating SCSI device shall apply driver precompensation to all the data signals, the P_CRCA
signal, the P1 signal, and the REQ, and or ACK signal. For paced DT DATA IN phases the
REQ/ACK offset specifies the maximum number of data valid state REQ assertions that shall be
sent by the TARG in advance of the number of ACK assertions received from the INIT. If the
number of data valid state REQ assertions exceeds the number of ACK assertions by the
REQ/ACK offset, the TARG will change P1 to enable the data invalid state prior to the next
assertion of REQ and will not change P1 to enable a data valid state until after the next ACK
assertion is received. For successful completion of a paced DT DATA IN phase the number of data
valid state REQ assertions and ACK assertions shall be equal. Each assertion indicates a single 32-
bit data transfer.
For paced DT DATA OUT phases the REQ/ACK offset specifies the maximum number of REQ
assertions that will be sent by the TARG in advance of the number of data valid state ACK
assertions received from the INIT. If the number of REQ assertions exceeds the number of data
valid state ACK assertions by the REQ/ACK offset, the TARG will not assert REQ until after the
next data valid state ACK assertion is received. For successful completion of a paced DT DATA
OUT phase the number of REQ assertions and data valid state ACK assertions shall be equal. Each
assertion indicates a single 32-bit data transfer. Implementors shall not use the following
subclauses for timing requirements.
(2) Paced transfer training pattern
If retain training information is disabled a training pattern shall be transferred at the start of the
first DT data phase for each data transfer direction after each physical connect and physical
reconnect. The training pattern shall not be transferred again until after a physical disconnection
occurs.
If the retain training information is enabled a training pattern shall be transferred at the start of the
first DT data phase for each data transfer direction after the retain training information is enabled.
The SCSI device shall save training configuration values for each I_T nexus that has negotiated to
retain training information. The SCSI device shall use the saved training configuration values for
all paced transfers. The TARG retrains an I_T nexus if it determines the training configuration
values are invalid, without having to renegotiate the retain training information protocol option.
C141-C011 1-75