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3–12
Hardware Interface
29 September 1997 – Subject To Change
21164PC Signal Names and Functions
pwr_fail_irq_h
I
1
Power failure interrupt request. This signal has multiple modes
of operation. During initialization, this signal is used to set up
sys_clk_out2_ h delay (see Table 4–3). During normal opera-
tion, this signal is used to signal a power failure.
srom_clk_h
O
1
Serial ROM clock. Supplies the clock that causes the SROM to
advance to the next bit. The cycle time of this clock is 128
times the cycle time of the CPU clock.
srom_data_h
I
1
Serial ROM data. Input for the SROM.
srom_oe_l
O
1
Serial ROM output enable. Supplies the output enable to the
SROM.
srom_present_l
1
B
1
Serial ROM present. Indicates that SROM is present and ready
to load the Icache.
st_clk1_h
O
1
STRAM clock. Clock for synchronously timed RAMs
(STRAMs). For Bcache, this signal is synchronous with
index_h<21:4> during private read and write operations, and
with sys_clk_out1_h during read and fill operations.
st_clk2_h
O
1
This signal is a duplicate of st_clk1_h, to increase the fanout
capability of the signal.
st_clk3_h
O
1
This signal is another duplicate of st_clk1_h, to increase the
fanout capability of the signal.
sys_clk_out1_h
O
1
System clock output. Programmable system clock
(cpu_clk_out_h divided by a value of 3 to 15) is used for
board-level cache and system logic.
sys_clk_out2_h
O
1
System clock output. A version of sys_clk_out1_h delayed by
a programmable amount from 0 to 7 CPU cycles.
sys_mch_chk_irq_h
I
1
System machine check interrupt request. This signal has multi-
ple modes of operation. During initialization, it is used to set
up sys_clk_out2_h delay (see Table 4–3). During normal
operation, it is used to signal a machine interrupt check
request.
sys_reset_l
I
1
System reset. This signal protects the 21164PC from damage
during initial power-up. It must be asserted until dc_ok_h is
asserted. After that, it is deasserted and the 21164PC begins its
reset sequence.
Table 3–1 21164PC Signal Descriptions
(Sheet 9 of 10)
Signal
Type Count Description