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7. UltraSPARC External Interfaces
Table 7-18 specifies the P_REPLY types.
7.13.2 S_REPLY
S_REPLY is a 4-bit physical interface between each SC and each UltraSPARC. SC
drives the S_REPLY pins radially to each UltraSPARC. Figure 7-23 shows the
S_REPLY packet format.
Figure 7-23 S_REPLY Packet Format
Table 7-18 P_REPLY Type Definitions
Type Definition
P_IDLE Idle. The default state when no reply is asserted. UltraSPARC drives P_IDLE after Power-On Reset.
P_RERR Read Error. Returned by UltraSPARC in response to a noncached block read request from SC. No data is
transferred. Cacheable read requests produce undefined results.
P_FERR Fatal Error. Indicates that system coherency has been lost and SC should generate a system-wide
Power-on-Reset (POR). UltraSPARC sends P_FERR when it detects a parity error on SYSADDR or in
the E-Cache tags. UltraSPARC can assert P_FERR at any time, not only in response to an S_REQ.
P_RAS Read ACK Single. UltraSPARC is ready to drive 16 bytes of read data on SYSDATA for the
P_NCRD_REQ request from SC. The next noncacheable P_REQ can be sent.
P_IAK Interrupt Acknowledge. Reply to a P_INT_REQ from SC. UltraSPARC acknowledges that the interrupt
transaction has been serviced; SC can send the next P_INT_REQ request and its data.
P_SACK Coherent Read ACK Block. Asserted for coherent S_REQ when the datum is in the cache and not pending
a Writeback due to victimization. If the S_REQ is for Copyback, P_SACK also indicates that
UltraSPARC is ready to transfer 64 bytes of data to SYSDATA.
P_SACKD Coherent Read ACK Block Dirty Victim. Asserted for S_INV_REQ or S_CPI_REQ when the datum has
been victimized and is pending a Writeback. SC can use this reply to cancel the subsequent Writeback
transaction for the dirty victim when this UltraSPARC issues it. UltraSPARC issues either P_SACK or
P_SACKD or S_CPB_REQ or S_CPD_REQ when the datum is pending a Writeback; no cancellation is
needed in this case. If the S_REQ is for Copyback, P_SACKD also indicates that UltraSPARC is ready to
transfer 64 bytes of data to SYSDATA.
P_SNACK NonExistent Block. No data is transferred. Reply to any coherent S_REQ with NDP=1 when the block
does not exist in the E-Cache. This is not a valid reply when NDP=0.
Type
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