System Port

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.

 

 

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 4–17shows the format of the 21264/EV68A ProbeResponse command.

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

X

X

 

 

 

 

 

 

[2:0]

 

 

 

 

 

 

 

 

 

 

 

Cycle 2

 

0

 

MS

MAF

X

X

 

 

 

 

 

 

[2:0]

 

 

 

 

 

 

 

 

 

 

 

Cycle 3

0

 

 

X

 

 

X

X

 

 

 

 

 

 

 

 

 

Cycle 4

 

 

X

 

 

X

X

 

 

 

 

 

 

 

 

 

4–24Cache and External Interfaces

21264/EV68A Hardware Reference Manual

Page 112
Image 112
Compaq ProbeResponse Commands Command40 =, Programming SETDIRTYENABLE20, 17 21264/EV68A ProbeResponse Command