Chapter 2. Programming Model
2-31
The MPC7400 Processor Register Set
The L2CR register can be accessed with the
mtspr
and
mfspr
instructions using SPR 1017.
20
L2HWF
L2 hardware ush. When the processor detects the value of L2HWF set to 1, the L2 will begin
a hardware ush. The ush will be done by starting with low cache indices and increment
these indices, for way 0 of the cache, one index at a time until the maximum index value is
obtained. Then, the index will be cleared to 0 and the same process is repeated for way 1 of
the cache. For each index and way of the cache, the processor will generate a castout
operation to the system bus for all modiTed 32-byte sectors. At the end of the hardware ush,
all lines in the L2 tag will be invalidated.
During the ush, all memory activity from the icache and dcache are blocked from accessing
the L2 until the ush is complete. Snoops, however, are fully serviced by the L2 during the
ush.
When the L2 Tags have been fully ushed of all valid entries, this bit will be reset to 0b0000 by
hardware. When this bit is cleared, it does not necessarily guarantee that all lines from the L2
have been written completely to the system interface. L2 copybacks can still be queued in the
bus interface unit.
Below is the code which must be run to use L2 hardware ush. When the Tnal
sync
completes, all modiTed lines in the L2 will have been written to the system address bus.
¥ Disable interrupts
¥
dssall
¥ sync
¥ set L2HWF
¥
sync
21
L2IO
L2 instruction-only.
Setting this bit enables instruction-only operation in the L2 cache. For this operation, only
transactions from the L1 instruction cache are allowed to be reloaded in the L2 cache. Data
addresses already in the cache will still hit for the L1 data cache. When both L2DO and L2IO
are asserted, the L2 cache is effectively locked.
22
L2CLKSTP
L2 clock stop.
Setting this bit enables the automatic stopping of the L2CLK_OUT signals for cache RAMs
that support this function. While L2CLKSTP is set, the L2CLK_OUT signals will automatically
be stopped when MPC7400 enters nap or sleep mode, and automatically restarted when
MPC7400 exits nap or sleep.
23
L2DRO
L2DLL rollover checkstop enable.
Setting this bit enables a potential rollover (or actual rollover) condition of the DLL to cause a
checkstop for the processor. A potential rollover condition occurs when the DLL is selecting
the last tap of the delay line, and thus can risk rolling over to the Trst tap with one adjustment
while in the process of keeping in sync. Such a condition is improper operation for the DLL,
and while this condition is not expected, this bit allows detection for added security. This bit
can be set when the DLL is Trst enabled (set with the L2CLK bits) to detect rollover during
initial synchronization. It can also be set when the L2 cache is enabled (with L2E bit) after the
DLL has achieved initial lock.
24D30
Reserved.
31
L2IP
L2 global invalidate in progress (read only).
This read-only bit indicates whether an L2 global invalidate is occurring. It should be
monitored after an L2 global invalidate has been initiated by the L2I bit to determine when it
has completed.
Table 2-17. L2CR Field Descriptions (Continued)
Bits
Name
Function