Compaq 21264 - Manual (Page 115)

Alpha 21264/EV67 Hardware Reference Manual Cache and External Interfaces 4–27
System Port
Table 4–20 describes the system-to-21264/EV67 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/EV67 Probe Commands Fields Descriptions
SysAddIn_L[14:0]
Field
Description
Probe[4:0] Probe type and next tag state (see Tables 4–21 and 4–22).
SysDc[4:0] Controls data movement in and out of the 21264/EV67. See Table 4–24 for a list of data
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/EV67 decrements its command outstand-
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.
C Commit bit. This bit decrements the uncommitted event counter (MB_CNTR) used for
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