dcgong2917 opened a new pull request, #19881:
URL: https://github.com/apache/nuttx/pull/19881
## Summary
Add a shared NuttX PWM lower-half for the Realtek Ameba PWM timer and wire
it up on three Ameba SoCs. A single PWM-capable timer provides one time
base
feeding several compare channels: every channel runs at the same frequency
while each carries its own duty cycle, exposed as a single `/dev/pwm0`
character device through the stock upper-half PWM driver (the
`CONFIG_PWM_NCHANNELS` multi-channel form).
- New shared driver `arch/arm/src/common/ameba/ameba_pwm.c/.h`, driven
through the SDK fwlib. The time-base entry points resolve from on-chip
ROM; the compare/capture helpers are pulled in from
`fwlib ram_common/ameba_tim.c` only when `CONFIG_AMEBA_PWM` is set.
- Per-chip constants (timer index, channel count, register base, input
clock, IRQ, clock-enable masks and the per-channel pad-mux code table)
live in each chip's `ameba_pwm_chip.h`, so a port to another Ameba chip
only supplies a same-named header.
- Board wiring and a `pwm` defconfig (running `examples/pwm`) for
`pke8721daf` (RTL8721DX, TIM8), `rtl8720f_evb` (RTL8720F, TIM4) and
`rtl8721f_evb` (RTL8721F, TIM4).
- `RTIM_` added to the `tools/nxstyle.c` mixed-case allow-list.
The series is 3 commits: the shared driver (on RTL8721DX), then RTL8720F,
then RTL8721F.
## Impact
New feature, opt-in via `CONFIG_AMEBA_PWM`. No change to existing
configurations or to other architectures; the code is only built when the
`pwm` config is selected on one of the three affected boards. Board
`index.rst` documentation is updated for all three boards in the same
commits.
## Testing
Host: Ubuntu on WSL2 (x86_64), arm-none-eabi-gcc.
Hardware-verified on all three boards; PWM output pads were probed with a
logic analyzer (channel 1 / channel 2): RTL8721DX PB18/PB19, RTL8720F
PA23/PA24, RTL8721F PA24/PA25.
For each board, run from NSH via `examples/pwm`:
| Command | Expected (channel 1) | Result |
| --- | --- | --- |
| `pwm -f 1000 -d 25 -t 10` | 1 kHz, 25 % duty | pass |
| `pwm -f 1000 -d 50 -t 10` | 1 kHz, 50 % duty | pass |
| `pwm -f 100 -d 50 -t 10` | 100 Hz, 50 % duty | pass |
| `pwm -f 20000 -d 50 -t 10` | 20 kHz, 50 % duty | pass |
| `pwm -f 1000 -d 25 -d 75 -t 10` | ch1 25 %, ch2 75 %, both 1 kHz | pass |
The last case exercises the multi-channel path: two independent compare
channels off one shared time base output different duty cycles at the same
frequency. Measured frequency error was < 1 %, and the output stopped
cleanly when the run duration elapsed.
`tools/checkpatch.sh -g master..HEAD` is clean on the whole series, and the
three `pwm` defconfigs match `make savedefconfig` output.
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