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esp32/machine_pwm: Keep duty constant when changing frequency.

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Save and restore the same duty cycle when the frequency (or frequency
resolution) is changed.  This allows a smooth frequency change.

Also update the esp32 PWM quickref to be clearer.
This commit is contained in:
IhorNehrutsa
2021-12-12 14:16:53 +02:00
committed by Damien George
parent 4189c64869
commit 09fe80d091
2 changed files with 39 additions and 36 deletions
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14
docs/esp32/quickref.rst
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@@ -224,14 +224,18 @@ Use the :ref:`machine.PWM <machine.PWM>` class::
from machine import Pin, PWM
pwm0 = PWM(Pin(0)) # create PWM object from a pin
pwm0.freq() # get current frequency (default 5kHz)
freq = pwm0.freq() # get current frequency (default 5kHz)
pwm0.freq(1000) # set PWM frequency from 1Hz to 40MHz
pwm0.duty() # get current duty cycle, range 0-1023 (default 512, 50%)
duty = pwm0.duty() # get current duty cycle, range 0-1023 (default 512, 50%)
pwm0.duty(256) # set duty cycle from 0 to 1023 as a ratio duty/1023, (now 25%)
duty_u16 = pwm0.duty_u16() # get current duty cycle, range 0-65535
pwm0.duty_u16(2**16*3//4) # set duty cycle from 0 to 65535 as a ratio duty_u16/65535, (now 75%)
pwm0.duty_u16() # get current duty cycle, range 0-65535
duty_ns = pwm0.duty_ns() # get current pulse width in ns
pwm0.duty_ns(250_000) # set pulse width in nanoseconds from 0 to 1_000_000_000/freq, (now 25%)
pwm0.duty_ns() # get current pulse width in ns
pwm0.deinit() # turn off PWM on the pin
pwm2 = PWM(Pin(2), freq=20000, duty=512) # create and configure in one go
@@ -246,7 +250,7 @@ Number of groups (speed modes) 2 1
Number of timers per group 4 4 4
Number of channels per group 8 8 6
----------------------------------------------------- -------- -------- --------
Different of PWM frequencies (groups * timers) 8 4 4
Different PWM frequencies (groups * timers) 8 4 4
Total PWM channels (Pins, duties) (groups * channels) 16 8 6
===================================================== ======== ======== ========