Compaq EV67 User Manual
Alpha 21264/EV67 Hardware Reference Manual
Cache and External Interfaces
4–21
System Port
System designers can minimize pin count for systems with a small memory by config-
uring both the bank interleave on cache block boundary mode and the page hit mode
formats into a short bus format. The pin SysAddOut_L[1] and/or SysAddOut_L[0]
are not used (selected by Cbox CSR SYS_BUS_SIZE[1:0]). Table 4–13 lists the values
for SYSBUS_FORMAT and SYS_BUS_SIZE[1:0] and shows the maximum physical
memory size.
uring both the bank interleave on cache block boundary mode and the page hit mode
formats into a short bus format. The pin SysAddOut_L[1] and/or SysAddOut_L[0]
are not used (selected by Cbox CSR SYS_BUS_SIZE[1:0]). Table 4–13 lists the values
for SYSBUS_FORMAT and SYS_BUS_SIZE[1:0] and shows the maximum physical
memory size.
Because addresses above the maximum PA are not visible to the external system, any
memory transaction generated to addresses above the maximum PA are detected and
converted to transactions to NXM (nonexistent memory) and processed internally by
the 21264/EV67.
memory transaction generated to addresses above the maximum PA are detected and
converted to transactions to NXM (nonexistent memory) and processed internally by
the 21264/EV67.
4.7.4 21264/EV67-to-System Commands Descriptions
Table 4–14 describes the 21264/EV67-to-system commands.
Table 4–13 Maximum Physical Address for Short Bus Format
SYSBUS_
FORMAT
FORMAT
SYSBUS_
SIZE[1:0]
SIZE[1:0]
Maximum PA
Comment
0
00
42
Bank interleave + full address
0
01
36
Bank interleave + SysAddOut_L[0] unused
0
10
Illegal
Illegal combination
0
11
34
Bank interleave + both SysAddOut_L[1:0] are used for I/O
1
00
38
Page hit mode + full address
1
01
36
Page hit mode + SysAddOut_L[0] unused
1
10
Illegal
Illegal combination
1
11
34
Page hit mode + both SysAddOut_L[1:0] are unused
Table 4–14 21264/EV67-to-System Commands Descriptions
Command
Command
[4:0]
[4:0]
Function
NOP
00000
The 21264/EV67 drives this command on idle cycles during reset. After
the clock forward reset period, the first NZNOP is generated and this
command is no longer generated.
the clock forward reset period, the first NZNOP is generated and this
command is no longer generated.
ProbeResponse
00001
Returns probe status and ID number of the VDB entry holding the
requested cache block.
requested cache block.
NZNOP
00010
This nonzero NOP helps to parse the command packet.
VDBFlushRequest
00011
VDB flush request. The 21264/EV67 sends this command to the system
when an internally generated transaction Bcache index matches a Bcache
victim or probe in the VDB. The system should flush VDB entries
associated with all probe and WrVictimBlk transactions that occurred
before this command.
when an internally generated transaction Bcache index matches a Bcache
victim or probe in the VDB. The system should flush VDB entries
associated with all probe and WrVictimBlk transactions that occurred
before this command.
MB
1
00111
Indicates an MB was issued, optional when Cbox CSR
SYSBUS_MB_ENA[0] is set.
SYSBUS_MB_ENA[0] is set.
ReadBlk
10000
Memory read.