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4–24 Cache and External Interfaces
21264/EV68A Hardware Reference Manual
System Port
Systems that require an explicit indication of ChangeToDirty status changes initi-
ated by STx_C instructions can assert Cbox CSR STC_ENABLE[0]. When this
register field = 000, CleanToDirty and SharedToDirty commands are used. The dis-
tinction between a ChangeToDirty command generated by a STx_C instruction and
one generated by a STx instruction is important to systems that want to service
ChangeToDirty commands with dirty data from a source processor. In this case, the
distinction between a locked exclusive instruction and a normal instruction is criti-
cal to avoid livelock for a LDx_L/STx_C sequence.
4.7.5 ProbeResponse Commands (Command[4:0] = 00001)
The 21264/EV68A responds to system probes that did not miss with a 4-cycle transfer
on SysAddOut_L[14:0]. As shown in Table 4–14, the Command[4:0] field for a Prob-
eResponse command equals 00001. Table 4–17 shows the format of the 21264/EV68A
ProbeResponse command.
Table 4–16 Programming SET_DIRTY_ENABLE[2:0]
SET_DIRTY_ENABLE
[2,0] (DS,CS,C) Cbox Action
000 Everything acknowledged internally (uniprocessor).
001 Only clean blocks generate external acknowledge (CleanToDirty commands only).
010 Only clean/shared blocks generate external acknowledge (SharedToDirty command
only).
011 Clean and clean/shared blocks generate external acknowledge.
100 Only dirty/shared blocks generate external acknowledge (SharedToDirty commands
only).
101 Only dirty/shared and clean blocks generate external acknowledge.
110 Only dirty/shared and clean/shared blocks generate external acknowledge.
111 All transactions generate external acknowledge.
Table 4–17 21264/EV68A ProbeResponse Command
SysAddOut_L[14:2] SysAddOut_L[1] SysAddOut_L[0]
Cycle 1 0 00001 Status[1:0] DM VS VDB
[2:0]
XX
Cycle 2 0 MS MAF
[2:0]
XX
Cycle 3 0 X X X
Cycle 4 X X X