Sun Microelectronics
120
UltraSPARC User’s Manual
S_REPLY takes a single interconnect clock cycle. SC asserts S_REPLY to initiate
data transfer to/from UltraSPARC and to acknowledge P_REQs from
UltraSPARC. Table 7-19 specifies the S_REPLY encodings.
SC must obey the following rules when generating S_REPLYs:
1.
There is no ordering of S_REPLYs between transaction classes. Within each
Class, however, S_REPLYs must be strongly ordered.
2.
Figure 7-24 on page 123 and Figure 7-25 on page 123 show S_REPLY timing
to the source and sink of data. UltraSPARC drives data 2 clock cycles after
receiving S_WAB, S_WAS, S_SRS or S_CRAB. UltraSPARC receives data 1
clock cycle after S_RBU, S_RBS, S_RAS, or S_SWIB.
3.
Figure 7-26 on page 123 shows S_REPLY read data timing after receiving a
P_REPLY from UltraSPARC. There are a minimum of two clock cycles
between when SC receives the P_REPLY and when it can send the
S_REPLY to initiate the data transfer. Figure 7-26 also shows the handshake
for delivering data to UltraSPARC.
4.
Figure 7-27 on page 124 shows the timing for back-to-back S_REQs for
Copyback. The earliest that SC can send another S_REQ to the same
UltraSPARC is the cycle after it sends the S_REPLY.
Table 7-19
S_REPLY Encoding
S_REPLY
Name
Reply to Transaction
Type
S_IDLE
Idle
Default State
0000
S_ERR
Error
Report Read Error
0001
S_CRAB
Coherent Read ACK Block
To slave for P_SACK or P_SACKD reply
0010
S_WBCAN Writeback Cancel
To master for P_WRB_REQ
0011
S_WAS
Write ACK Single
To master for P_NCWR_REQ
0100
S_WAB
Write ACK Block
To master for any block write
0101
S_OAK
Ownership ACK
To master for P_RDO_REQ
0110
S_INAK
Interrupt NACK
To master for P_INT_REQ
0111
S_RBU
Read Block ACK Unshared To master for any block read
1000
S_RBS
Read Block ACK Shared
To master for coherent shared read
1001
S_RAS
Read ACK Single
To master for P_NCRD_REQ
1010
S_RTO
Read Time Out
To master, forwarding P_RTO, read to unimplemented address
1011
S_SRS
Slave Read Single
Read 16 bytes of data from slave
1110
S_SWIB
Slave Write Interrupt Block Write 64 bytes of interrupt data to slave
1101
Reserved
—
—
1111
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