Compaq EV68A Manual De Usuario
21264/EV68A Hardware Reference Manual
Cache and External Interfaces
4–27
System Port
Table 4–20 describes the system-to-21264/EV68A probe commands fields descriptions.
The probe command field Probe[4:0] has two sections, Probe[4:3] and Probe[2:0].
Table 4–21 lists the data movement selected by Probe[4:3].
Table 4–22 lists the next cache block state selected by Probe[2:0].
Table 4–20 System-to-21264/EV68A Probe Commands Fields Descriptions
SysAddIn_L[14:0]
Field
Field
Description
Probe[4:0]
SysDc[4:0]
Controls data movement in and out of the 21264/EV68A. See Table 4–24 for a list of data
movement types.
movement types.
RVB
Clears the victim or I/O write buffer (IOWB) valid bit specified in ID[3:0].
RPB
Clears probe valid bit specified in ID[2:0].
A
Command acknowledge. When set, the 21264/EV68A decrements its command outstand-
ing counter (SYSBUS_ACK_LIMIT[4:0]).
ing counter (SYSBUS_ACK_LIMIT[4:0]).
ID[3:0]
Identifies the victim data buffer (VDB) number or the I/O write buffer (IOWB) number.
Bit [3] is only asserted for the IOWB.
Bit [3] is only asserted for the IOWB.
C
Commit bit. This bit decrements the uncommitted event counter (MB_CNTR) used for
MB acknowledge.
MB acknowledge.
Table 4–21 Data Movement Selection by Probe[4:3]
Probe[4:3]
Data Movement Function
00
NOP
01
Read if hit, supply data to system if block is valid.
10
Read if dirty, supply data to system if block is valid/dirty.
11
Read anyway, supply data to the system at index of probe.
Table 4–22 Next Cache Block State Selection by Probe[2:0]
Probe[2:0]
Next Tag State
000
NOP
001
Clean
010
Clean/Shared
011
Transition3
1
: Clean
⇒ Clean/Shared
Dirty
⇒ Invalid
Dirty/Shared
⇒ Clean/Shared
100
Dirty/Shared