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E–12 Alpha Architecture Handbook
E.2.2.3 OpenVMS Alpha and DIGITAL UNIX Functions and Arguments
The functions execute only on a single (the current running) processor and are described in
Table E–4.
The OpenVMS Alpha MTPR_PERFMON instruction is called with a function code in R16, a
function-specific argument in R17, and status is returned in R0.
The DIGITAL UNIX wrperfmon instruction is called with a function code in a0, a function
specific argument in a1, and status is returned in v0.
9–8
MODE_SELECT
1
Select modes in which to count:
7–4 PCSEL1 Counter 1 selection. See Table E–13
3–0 PCSEL2 Counter 2 selection. See Table E–14
1
Windows NT Alpha uses bits 30 and 9–8 differently than as documented in the 21164 Hard-
ware Reference Manual; it uses the processor executive mode to run user (nonprivileged)
code. Therefore, bit 30 is always set to one and bits 9–8 are used to select the mode.
Table E–4: OpenVMS Alpha and DIGITAL UNIX Performance Monitoring
Functions
Function Register Usage Comments
Enable performance monitoring; do not reset counters
DIGITAL UNIX
Input: a0 = 1 Function code value
a1 = arg Argument from Table E–5
Output: v0 = 1 Success
v0 = 0 Failure (not generated)
OpenVMS Alpha
Input: R16 = 1 Function code value
R17 = arg Argument from Table E–5
Output: R0 = 1 Success
R0 = 0 Failure (not generated)
Table E–3: Bit Summary of PMCTR Register for Windows NT Alpha
(Continued)
Bits Name Meaning
Value Meaning
0 Count all modes
1 Count PALmode only
2 Count all modes except PALmode
3 Count only user mode