User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 4: System Control and Debug Unit
Page
61
S
YSTEM
P
ERFORMANCE
C
OUNTERS
There are four system performance counters. They count system events and interrupt when saturated. All four
counters are cleared and/or enabled simultaneously. When one counter saturates, all counters are frozen.
Thus, the readings across the four counters cover the same interval. The counters are writable; if they are
written while active the count will continue from the new value (note that the time from the CPU issuing a store
to the counter getting the new value is UNPREDICTABLE).
The counters are all controlled by the
perf_cnt_cfg
register. This is used to configure the count source for each
counter, to enable or disable all the counters and to clear all the counters. The counter clear bit is write only,
the counters will all be cleared to zero at the end of the cycle that this bit is written with a 1. If both the enable
and clear bits are written with 1 in the same write, the counters are cleared and will start counting the cycle
after the write completes.
If any counter reaches its maximum count the counters will all be disabled (the enable bit in the
perf_cnt_cfg
register is cleared) and the perf_cnt_int interrupt will be raised. The interrupt is removed and all the counters
are cleared when the clear bit in the
perf_cnt_cfg
register is written with a 1.
Since it takes a cycle to disable the counters there is one additional cycle sampled after one (or more) of the
counts reaches
FF_FFFF_FFFF
during which the counter may overflow (if its source is still active). There is
an additional bit in the performance counters that gets set when they overflow, thus the counter (or counters)
that disabled monitoring could have the value
FF_FFFF_FFFF
or
100_0000_0000
when the interrupt is seen.
Table 29: ZBbus Count Register
zbbus_cycle_count -
00_1003_0000
READ ONLY
Note
00_1003_0008 - 00_1003_FFFF
is safe for user space access
Bits
Name
Default
Description
63:0
count
64'h0
Count of ZBbus cycles since reset. Writes will be ignored.
Table 30: ZBbus Count Compare Registers
zbbus_cycle_cp0 -
00_1002_0C00
zbbus_cycle_cp1 -
00_1002_0C08
Bits
Name
Default
Description
63:0
compare
64'hFFFF_FFFF
_FFFF_FFFF
Value is compared to zbbus_cycle_count and the interrupt corresponding to
the register is raised when the count is equal to the value. The interrupt is
cleared by any write to the compare register.
Table 31: System Performance Counter Configuration Registers
perf_cnt_cfg -
00_1002_04C0
Bits
Name
Default
Description
7:0
Counter 0 source
8'b0
Sets the source for counter 0.
15:8
Counter 1 source
8'b0
Sets the source for counter 1.
23:16
Counter 2 source
8'b0
Sets the source for counter 2.
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