Compaq EV68A specifications Initialization Mode Processing, Evictenable BCWRTSTS30 Bcbankenable

Initialization Mode Processing

Table 7–9 WRITE_MANY Chain CSR Values for Bcache Initialization (Continued)

WRITE_MANY Chain CSRs	Required Value at Initialization Mode
EVICT_ENABLE	0
BC_WRT_STS[3:0]	0
BC_BANK_ENABLE	0

Except for INIT_MODE, all the CSR registers have been described in earlier sections. When asserted, INIT_MODE has the following behavior:

•Cache block updates to the Dcache set the block to the Clean state.

•Updates to the Bcache use the BC_WRT_STS[3:0] bits.

•WrVictimBlk command generation to the system interface are squashed.

Using the INVAL_TO_DIRTY_ENABLE and INIT_MODE registers, initialization code loaded from the SROM can generate and delete blocks inside the 21264/EV68A without system interaction. This behavior is very useful for initialization and startup processing, when the system interfaces are not fully functional. Figure 7–4shows a code example for initializing Bcache.

Figure 7–4 Example for Initializing Bcache

Reset chip and load Icache with this code
set init_mode	;now all WrVictims are ignored
	;bc_enable_a	1
	;zeroblk_enable_a	1
	;set_dirty_enable_a	0
	;init_mode_a	1
	;enable_evict_a	0
	;bc_wrt_sts_a	0
	;bc_bank_enable_a	0
	;bc_size_a	15
	;now all writes to Bcache actually invalidate
	;the Bcache. (if space was needed for scratch
	;pad, the status bits could just as
	;well be Valid)
for 2 X bc_size	;This loop generates legal ECC data, and
{ WH64 address }	;invalidate tags which are written to the
	;Bcache for all but the final 64KB of address.
turn_off_bcache:	;bc_enable_a	0
	;init_mode_a	0
	;bc_size_a	0
	;zeroblk_enable_a	1
	;enable_evict_a	0
	;set_dirty_enable_a	0
	;bc_bank_enable_a	0
	;bc_wrt_sts_a	0

21264/EV68A Hardware Reference Manual Initialization and Configuration 7–13