Sun Microelectronics
122
UltraSPARC User’s Manual
Table 7-20
S_REPLY Type Definitions
Type
Definition
S_IDLE
Idle. Default state; no reply is asserted. SC should drive S_IDLE after Power-On Reset.
S_RTO
Read Time-out. No data is transferred. SC uses S_RTO to indicate time-outs on read transactions.
UltraSPARC generates an
instruction_access_error
or
data_access_error
exception and logs time out status
in the Asynchronous Fault Status Register.
S_ERR
Error. No data is transferred. SC asserts S_ERR for implementation-specific bus errors detected on read
transactions. UltraSPARC generates an
instruction_access_error
or
data_access_error
exception and logs
bus error status in the AFSR.
S_WAS
Write ACK Single to UltraSPARC. SC commands UltraSPARC’s output data queue to drive 16 bytes of
data on SYSDATA in response UltraSPARC prior P_NCWR_REQ request.
S_WAB
Write ACK Block to UltraSPARC. SC commands UltraSPARC’s output data queue to drive 64 bytes of
data on SYSDATA in response to UltraSPARC’s prior P_NCBWR_REQ, P_WRB_REQ, P_WRI_REQ, or
P_INT_REQ request.
S_OAK
Ownership ACK Block to UltraSPARC. No data is transferred. SC generates S_OAK in response to a
P_RDO_REQ from an UltraSPARC that has the data in its E-Cache but needs write permission on it.
S_RBU
Read Block Unshared ACK to UltraSPARC. SC commands the requesting UltraSPARC’s input data queue
to receive 64 bytes of unshared or noncached data on SYSDATA. Issued in response to a P_RDS_REQ,
P_RDO_REQ, or P_NCBRD_REQ request from UltraSPARC.
S_RBS
Read Block Shared ACK to UltraSPARC. SC commands the requesting UltraSPARC’s input data queue to
receive 64 bytes of shared data on SYSDATA. Issued in response to a P_RDS_REQ, P_RDSA_REQ, or
P_RDD_REQ request from UltraSPARC.
S_RAS
Read ACK Single to UltraSPARC. SC commands the requesting UltraSPARC’s input data queue to
receive 16 bytes of data on SYSDATA. Issued in response to a P_NCRD_REQ request from UltraSPARC.
S_CRAB
Copyback Read Block ACK to UltraSPARC. SC commands the output data queue of the UltraSPARC that
contains the block to drive 64 bytes of copyback data on SYSDATA. Issued in response to a P_SACK or
P_SACKD reply from UltraSPARC containing the block. This is last step in a cache-to-cache transfer
sequence in which the requesting UltraSPARC receives data from the copyback UltraSPARC. The entire
sequence is P_RD*_REQ
→
S_CBP_REQ / S_CPI_REQ / S_CPD_REQ
→
P_SACK / P_SACKD
→
S_CRAB. The S_CRAB reply allows SC to send the next coherent S_REQ transaction (S_INV_REQ,
S_CPI_REQ, S_CPB_REQ, or S_CPD_REQ).
S_SWIB
Interrupt Write Block ACK to UltraSPARC. SC commands target UltraSPARC’s Incoming Interrupt Vector
Data registers to accept 64 bytes of interrupt data from SYSDATA. (The registers actually receive only
the low-order 64 bits of each of the first three 128-bit data words, even though the entire 64 bytes is
transferred on the bus.) In parallel (on SYSADDR), SC forwards the P_INT_REQ request associated
with this block to the Interrupt Request Register of the target UltraSPARC.
S_WBCAN Writeback Cancel ACK to UltraSPARC. SC generates S_WBCAN if a previously sent P_WRB_REQ must
be cancelled. No data is transferred.
S_INAK
Interrupt NACK. No Data is transferred. SC generates S_INAK (instead of S_WAB) to NACK the source
UltraSPARC’s P_INT_REQ request when the interrupt target cannot accept another interrupt packet.
UltraSPARC records the NACK status in its Interrupt Vector Dispatch Register, signalling software to
retry sometime later. This is the only transaction that is NACKed by SC.
S_SRS
Slave Read Single. SC commands the output data queue of the slave port to drive 16 bytes of data on
SYSDATA in response to the slave’s P_RAS reply.
S_SRB
Slave Read Block. SC commands the output data queue of the slave port to drive 64 bytes of data on SYS-
DATA in response to the slave’s P_SACK reply. UltraSPARC never receives this S_REPLY.
S_SWB
Slave Write Block. SC commands the input data queue of the slave port to read 64 bytes of data from
SYSDATA in response to the slave’s P_SACK reply. UltraSPARC never receives this S_REPLY.
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