Sun Microelectronics
108
UltraSPARC User’s Manual
If NDP=1, UltraSPARC replies with:
• P_SACK if the block is in the E-Cache.
• P_SACKD if the block has been victimized from the E-Cache but not yet
written back.
• P_SNACK if the block is not present in the E-Cache or the writeback buffer.
The P_SACK or P_SACKD reply indicates that UltraSPARC is ready to transfer
the requested data. SC initiates the data transfer by sending S_CRAB. If NDP=0
and the block was not present in the cache, UltraSPARC drives undefined data in
response to the S_CRAB.
UltraSPARC responds more quickly if NDP=0; SC should assert NDP only in sys-
tems that do not support Dtags. Section 7.10, “S_REQ,” on page 111 for more tim-
ing information.
SC can buffer the P_SACKD reply and cancel the P_WRB_REQ when it appears.
UltraSPARC-I supports one outstanding coherent system request. SC can send its
next coherent request on the cycle after the S_CRAB reply.
7.7.10 CopybackToDiscard (S_CPD_REQ)
Non-destructive copyback request from SC to UltraSPARC. Generated by SC to
service a ReadToDiscard (P_RDD_REQ) request from another processor. This
transaction does not generate a state change for the E-Cache line.
No state change in Etag.
UltraSPARC issues its P_REPLY depending on the state of the E-Cache line and
the setting of the No Dual tag Present (NDP) bit in the S_CPI_REQ.
If NDP=0, UltraSPARC replies with:
• P_SACK if the block is in the E-Cache. UltraSPARC also asserts P_SACK if the
block is not in the cache, but this is an error condition in systems that support
Dtags (NDP=0).
• P_SACKD if the block has been victimized from the E-Cache but not yet
written back
If NDP=1, UltraSPARC replies with:
• P_SACK if the block is in the E-Cache.
• P_SACKD if the block has been victimized from the E-Cache but not yet
written back.
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