Compaq ECQD2KCTE Laptop User Manual


 
Instruction Descriptions 4–143
4.11.8 Read Processor Cycle Counter
Format:
Operation:
Ra {cycle counter}
Exceptions:
Instruction mnemonics:
Qualifiers:
Description:
Register Ra is written with the processor cycle counter (PCC). The PCC register consists of
two 32-bit fields. The low-order 32 bits (PCC<31:0>) are an unsigned, wrapping counter,
PCC_CNT. The high-order 32 bits (PCC<63:32>), PCC_OFF, are operating-system depen-
dent in their implementation.
See Section 3.1.5 for a description of the PCC.
If an operating system uses PCC_OFF to calculate the per-process or per-thread cycle count,
that count must be derived from the 32-bit sum of PCC_OFF and PCC_CNT. The following
example computes that cycle count, modulo 2**32, and returns the count value in R0. Notice
the care taken not to cause an unwanted sign extension.
RPCC R0 ; Read the process cycle counter
SLL R0, #32, R1 ; Line up the offset and count fields
ADDQ R0, R1, R0 ; Do add
SRL R0, #32, R0 ; Zero extend the count to 64 bits
The following example code returns the value of PCC_CNT in R0<31:0> and all zeros in
R0<63:32>.
RPCC R0
ZAPNOT R0,#15,R0
RPCC Ra.wq
!Memory format
None
RPCC Read Processor Cycle Counter
None