methodmissing opened a new pull request, #20522:
URL: https://github.com/apache/nuttx/pull/20522
## Summary
`CONFIG_ARCH_PERF_EVENTS` defaults to on for ARMv7-M, but the imxrt port
never calls
`up_perf_init()`, so the DWT cycle counter is never enabled and
`perf_gettime()` returns zero.
Anything timed with it reports nothing: `rpmsg ping` prints 0 ns for min,
average and maximum and a
rate of 4294.967295 Mbits/s. Call `up_perf_init()` with
`BOARD_CPU_FREQUENCY` in `imxrt_start.c`
after the MPU is set up, as samv7 and stm32h7 do. Every imxrt board defines
that macro.
Found while bringing up the RT1170 CM4 RPTUN backend (apache/nuttx#TBD);
independent of it.
## Impact
* New feature: NO. Existing feature changed: YES, perf counters on imxrt now
count.
* User: perf-timed output becomes meaningful. Build: NO. Hardware: imxrt,
all parts.
* Documentation: NO. Security: NO. Compatibility: NO.
## Testing
* Host: macOS, GNU Arm Embedded 9-2020-q2 (gcc 9.3.1), standalone
`fmu-v6xrt:rptun` on
apache/nuttx master with apache/nuttx-apps master.
* Target: Pixhawk 6X-RT (i.MX RT1176 rB0), stock nsh over USB CDC/ACM, with
the RT1170 RPTUN
backend and a CM4 remote to ping.
Logs before change:
```
nsh> rpmsg ping /dev/rpmsg/cm4 100 64 3 0
nsh> dmesg
ping times: 100
buffer_len: 1008, send_len: 64
avg: 0 s, 0 ns
min: 0 s, 0 ns
max: 0 s, 0 ns
rate: 4294.967295 Mbits/sec
```
Logs after change:
```
nsh> rpmsg ping /dev/rpmsg/cm4 100 64 3 0
nsh> dmesg
ping times: 100
buffer_len: 1008, send_len: 64
avg: 0 s, 18208 ns
min: 0 s, 16215 ns
max: 0 s, 47375 ns
rate: 28.119507 Mbits/sec
```
## PR verification Self-Check
* [x] This PR introduces only one functional change.
* [x] I have updated all required description fields above.
* [x] My PR adheres to Contributing Guidelines and Documentation.
* [ ] My PR is still work in progress (not ready for review).
* [x] My PR is ready for review and can be safely merged into a codebase.
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