Porting PR #8040 by @hoihu to SAMD, following the commit
5873390226.
One small addition: before executing keyboard interrupt, the input buffer
is cleared.
The SAMD21 implementation is an adaption of @jimmo's code for STM32Lxx.
The only changes are the addresses and names of the port registers and the
timing parameters.
SAMD21: The precision is about +/-25ns at 48MHz clock frequency. The first
two cycles are about 40-60 ns longer than set. But still good enough to
drive a neopixel device.
SAMD51: The precision is about +/-30ns at 120MHz clock frequency. Good
enough to drive a neopixel device.
And use mp_hal_ticks_us() for SAM21's mp_hal_ticks_cpu(). The SAMD21 has
no CYCCNT register, and the SysTick register has only a 1 ms span (== 48000
count range).
Features are:
- 3 to 5 different frequency groups.
- Freq range of 1Hz - 24 MHz.
- Duty rate stays stable on freq change.
Keyword options to the PWM constructor:
- device=n Select a specific PWM device. If no device is specified, a free
device is chosen, if available at that pin.
- freq=nnnn
- duty_u16=nnnn
- duty_ns=nnnn
- invert=True/False Allowing two outputs on the same device/channel to have
complementary signals.
If both freq and duty are provided, PWM output will start immediately.
Pins at the same device have the same frequency. If the PWM output number
exceeds the number of channels at the PWM device, the effctive channel_no
is output_no % channel_count. So with a channel count of 4, output 7 is
assigned to channel 3. Pins at a certain channel have the same frequency
and duty rate, but may be seperately inverted.
Changes in this commit are:
- Use mphal_xx functions whenever possible.
- Remove obsolete includes.
- Clean up traces of a non-functional pin.irq() from earlier builds.
Pin.irq() will be added in further commits in a working manner.
The changes in this commit are:
- Add an interface for pin open-drain mode.
- Improve ticks_us() by using the us-counter.
- Improve ticks_cpu() by using the CPU's SysTick.
- Makefile: update to use new ASF4 files, support frozen manifest, and
include source files in upcoming commits
- boards/manifest.py: add files to freeze
- boards/samd51p19a.ld: add linker script for this MCU
- help.c: add custom help text
- main.c: execute _boot.py, boot.py and main.py on start-up
- modules/_boot.py: startup file to freeze
- modutime.c: add gmtime, localtime, mktime, time functions
- mpconfigport.h: enabled more features for sys and io and modules
- mphalport.h: add mp_hal_pin_xxx macros
- mphalport.c: add mp_hal_stdio_poll
