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esp32: PWM duty will be changed when changing the frequency if more than one channel is used. #8345

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esp32: PWM duty will be changed when changing the frequency if more than one channel is used.#8345

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@Dreagonmon
Dreagonmon
opened on Feb 23, 2022

After upgrading mpy from 1.17 to 1.18, my buzzer can't play low frequency sounds any more.

With further test, it shows that the pwm has no output when frequencies < 611Hz.

from machine import PWM, Pin
pwm = PWM(Pin(5)) # also tested with Pin(2)
pwm.duty(512)
pwm.freq(611) # it works, digital multimeters shows freq 1222Hz
pwm.freq(610) # no pwm output, digital multimeters says freq is 0

And after switching back to mpy 1.17, pwm.freq(610) works fine. I'v tested with another board and I still got the same result. I'm sure this is an issue introduced by v1.18.

Activity

  1. Dreagonmon
    closed this as completedon Feb 23, 2022

  2. xky183 commented on Feb 26, 2022

    @xky183
    xky183
    on Feb 26, 2022

    meet same problem by v1.18，work fine by v1.17

  3. robert-hh commented on Feb 26, 2022

    @robert-hh
    robert-hh
    on Feb 26, 2022
    Contributor

    Fixed since a while. Please use a recent nightly build, and ignore the "unstable" label. The nightly builds are tested the same way than the release build.

  4. xky183 commented on Feb 26, 2022

    @xky183
    xky183
    on Feb 26, 2022

    Fixed since a while. Please use a recent nightly build, and ignore the "unstable" label. The nightly builds are tested the same way than the release build.

    Thank you very much，I just tested the version "esp32-20220226-unstable-v1.18-160-g0a217624e.bin", it can work in 1Hz now, but... the duty will be changed when changing the freq.

    >>> 
>>> pwm0
PWM(Pin(0), freq=2, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(200)
>>> pwm0
PWM(Pin(0), freq=200, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=2003, duty=1024, resolution=15, (duty=100.00%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.duty(512)
>>> pwm0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=20000, duty=8192, resolution=11, (duty=800.00%, resolution=0.049%), mode=0, channel=0, timer=1)
>>> pwm0.duty(512)
>>> pwm0.freq(20000)
>>> pwm0
PWM(Pin(0), freq=20000, duty=512, resolution=11, (duty=50.00%, resolution=0.049%), mode=0, channel=0, timer=1)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=2003, duty=32, resolution=15, (duty=3.13%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.duty(512)
>>> pwm0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.freq(200)
>>> pwm0
PWM(Pin(0), freq=200, duty=256, resolution=16, (duty=25.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.duty(512)
>>> pwm0
PWM(Pin(0), freq=200, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(20)
>>> pwm0
PWM(Pin(0), freq=20, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2)
>>> pwm0
PWM(Pin(0), freq=2, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>>

  5. Dreagonmon commented on Feb 26, 2022

    @Dreagonmon
    Dreagonmon
    on Feb 26, 2022
    Author

    maybe #8306 is the related issue.

    I created this issue and closed it soon when I realized that this is fixed in the nightly build. but it seems not really fixed.

  6. robert-hh commented on Feb 26, 2022

    @robert-hh
    robert-hh
    on Feb 26, 2022
    Contributor

    No. It is not. That is something which show up only once after hard reset. I just tested you sequence with my own builds, and it works fine. I just downloaded the nightly build and verify, which esp-idf and version is used.

  7. robert-hh commented on Feb 26, 2022

    @robert-hh
    robert-hh
    on Feb 26, 2022
    Contributor

    I cannot verify your findings. Everything looks as intended. Both the reporting in the print and the actual signal are fine.

    MicroPython v1.18 on 2022-02-26; ESP32 module (spiram) with ESP32
Type "help()" for more information.
>>> p0=PWM(Pin(0), 2, duty=512)
>>> p0
PWM(Pin(0), freq=2, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> p0.freq(200)
>>> p0
PWM(Pin(0), freq=200, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> p0.freq(2000)
>>> p0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=0)
>>> p0.freq(20000)
>>> p0
PWM(Pin(0), freq=20000, duty=512, resolution=11, (duty=50.00%, resolution=0.049%), mode=0, channel=0, timer=0)
>>> p0.freq(2000)
>>> p0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=0)
>>> p0.freq(200)
>>> p0
PWM(Pin(0), freq=200, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> p0.freq(2)
>>> p0
PWM(Pin(0), freq=2, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> import platform
>>> platform.platform()
'MicroPython-1.18.0-xtensa-IDFv4.2.2-with-newlib3.0.0'
>>>

  8. xky183 commented on Feb 27, 2022

    @xky183
    xky183
    on Feb 27, 2022

    I test twice，
    at the first time，only use one PWM0 channel，it works well。
    at the second time，use PWM0,PWM2,PWM4 channel，it seems timers for each pwm channel will be changed when changing the freq, and it will cause the changing of duty , maybe the problem is the counter of the timer is not set right value，

    `>>> 
>>> from machine import PWM
>>> pwm0 = PWM(Pin(0), freq=2, duty=512)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'Pin' isn't defined
>>> from machine import Pin
>>> pwm0 = PWM(Pin(0), freq=2, duty=512)
>>> pwm0
PWM(Pin(0), freq=2, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(20)
>>> pwm0
PWM(Pin(0), freq=20, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(200)
>>> pwm0
PWM(Pin(0), freq=200, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=0)
>>> pwm0.freq(20000)
>>> pwm0
PWM(Pin(0), freq=20000, duty=512, resolution=11, (duty=50.00%, resolution=0.049%), mode=0, channel=0, timer=0)
>>> pwm0.freq(200000)
>>> pwm0
PWM(Pin(0), freq=200000, duty=512, resolution=8, (duty=50.00%, resolution=0.391%), mode=0, channel=0, timer=0)
>>> pwm0.freq(20000)
>>> pwm0
PWM(Pin(0), freq=20000, duty=512, resolution=11, (duty=50.00%, resolution=0.049%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=0)
>>> pwm0.freq(200)
>>> pwm0
PWM(Pin(0), freq=200, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(20)
>>> pwm0
PWM(Pin(0), freq=20, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2)
>>> pwm0
PWM(Pin(0), freq=2, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> ets Jun  8 2016 00:22:57

rst:0x1 (POWERON_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:4540
ho 0 tail 12 room 4
load:0x40078000,len:12344
ho 0 tail 12 room 4
load:0x40080400,len:4124
entry 0x40080680
MicroPython v1.18 on 2022-02-26; ESP32 module with ESP32
Type "help()" for more information.
>>> from machine import Pin
>>> from machine import PWM
>>> pwm0 = PWM(Pin(0), freq=2, duty=512)
>>> pwm2 = PWM(Pin(2), freq=200, duty=512)
>>> pwm4 = PWM(Pin(4), freq=2000, duty=512)
>>> pwm0
PWM(Pin(0), freq=2, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(20)
>>> pwm0
PWM(Pin(0), freq=20, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(200)
>>> pwm0
PWM(Pin(0), freq=200, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=1)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=2003, duty=1024, resolution=15, (duty=100.00%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.duty(512)
>>> pwm0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.freq(20000)
>>> pwm0
PWM(Pin(0), freq=20000, duty=512, resolution=11, (duty=50.00%, resolution=0.049%), mode=0, channel=0, timer=0)
>>> pwm0.freq(200000)
>>> pwm0
PWM(Pin(0), freq=200000, duty=512, resolution=8, (duty=50.00%, resolution=0.391%), mode=0, channel=0, timer=0)
>>> pwm0.freq(20000)
>>> pwm0
PWM(Pin(0), freq=20000, duty=512, resolution=11, (duty=50.00%, resolution=0.049%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=2003, duty=32, resolution=15, (duty=3.13%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.duty(512)
>>> pwm0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.freq(200)
>>> pwm0
PWM(Pin(0), freq=200, duty=256, resolution=16, (duty=25.00%, resolution=0.002%), mode=0, channel=0, timer=1)
>>> pwm0.duty(512)
>>> pwm0
PWM(Pin(0), freq=200, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=1)
>>> pwm0.freq(20)
>>> pwm0
PWM(Pin(0), freq=20, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2)
>>> pwm0
PWM(Pin(0), freq=2, duty=512, resolution=16, (duty=50.00%, resolution=0.002%), mode=0, channel=0, timer=0)
>>> import platform
>>> platform.platform()
'MicroPython-1.18.0-xtensa-IDFv4.2.2-with-newlib3.0.0'
>>> 
>>> 
>>> `

  9. xky183 commented on Feb 27, 2022

    @xky183
    xky183
    on Feb 27, 2022

    maybe #8306 is the related issue.

    I created this issue and closed it soon when I realized that this is fixed in the nightly build. but it seems not really fixed.

    could you reopen this issue? thanks

  10. robert-hh commented on Feb 27, 2022

    @robert-hh
    robert-hh
    on Feb 27, 2022
    Contributor

    You are right. If more than one channel is used, there will be issues with the duty cycle. The basic PR which changed that behavior is #7817. The PR message explains the function and one can see the root of the problem, which is also visible in your log. If a channel's frequency is set to a frequency used by the other channel, it uses this channels timer. That does not take care of potentially different duty cycles.
    Dropping the timer re-use mechanism makes the PWM work as intended. However, it is then again limited to 8 channels.

  11. Dreagonmon commented on Feb 27, 2022

    @Dreagonmon
    Dreagonmon
    on Feb 27, 2022
    Author

    could you reopen this issue? thanks

    sure

  12. Dreagonmon
    reopened this on Feb 27, 2022
  13. Dreagonmon
    changed the title [-]esp32: PWM has no output when frequencies < 611Hz.[/-] [+]esp32: PWM duty will be changed when changing the frequency if more than one channel is used.[/+] on Feb 27, 2022

  14. robert-hh commented on Feb 27, 2022

    @robert-hh
    robert-hh
    on Feb 27, 2022
    Contributor

    So I made a small change to the code which forces the duty rate to be set on frequency changes. That was omitted when setting to a frequency which was already used in a different channel. The timer for that channel was reused, but still the duty rate had to be adapted. The change is based on a different PR I made earlier, and by chance it fixes #8306 as well. Output from going though the same series as @xky183 above:

    MicroPython v1.18-160-g0a217624e-dirty on 2022-02-27; ESP32 module (spiram) with ESP32
Type "help()" for more information.
>>> import platform
>>> platform.platform()
'MicroPython-1.18.0-xtensa-IDFv4.2.2-dirty-with-newlib3.0.0'
>>> pwm0 = PWM(Pin(0), freq=2, duty=512)
>>> pwm2 = PWM(Pin(22), freq=200, duty=512)
>>> pwm4 = PWM(Pin(4), freq=2000, duty=512)
>>> pwm0
PWM(Pin(0), freq=2, duty=512, resolution=18, (duty=50.00%, resolution=0.000%), mode=0, channel=0, timer=0)
>>> pwm0.freq(20)
>>> pwm0
PWM(Pin(0), freq=20, duty=512, resolution=20, (duty=50.00%, resolution=0.000%), mode=0, channel=0, timer=0)
>>> pwm0.freq(200)
>>> pwm0
PWM(Pin(0), freq=200, duty=512, resolution=18, (duty=50.00%, resolution=0.000%), mode=0, channel=0, timer=1)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.freq(20000)
>>> pwm0
PWM(Pin(0), freq=20000, duty=512, resolution=11, (duty=50.00%, resolution=0.049%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2000)
>>> pwm0
PWM(Pin(0), freq=2003, duty=512, resolution=15, (duty=50.00%, resolution=0.003%), mode=0, channel=0, timer=2)
>>> pwm0.freq(200)
>>> pwm0
PWM(Pin(0), freq=200, duty=512, resolution=18, (duty=50.00%, resolution=0.000%), mode=0, channel=0, timer=1)
>>> pwm0.freq(20)
>>> pwm0
PWM(Pin(0), freq=20, duty=512, resolution=20, (duty=50.00%, resolution=0.000%), mode=0, channel=0, timer=0)
>>> pwm0.freq(2)
>>> pwm0
PWM(Pin(0), freq=2, duty=512, resolution=18, (duty=50.00%, resolution=0.000%), mode=0, channel=0, timer=0)
>>>
  15. dpgeorge
    added a commit that references this issue on Mar 7, 2022

    esp32/machine_pwm: Always set the duty cycle when setting the frequency.

    55a0125

  16. dpgeorge commented on Mar 7, 2022

    @dpgeorge
    dpgeorge
    on Mar 7, 2022
    Member

    Fixed by 55a0125

  17. dpgeorge
    closed this as completedon Mar 7, 2022
  18. Wind-stormger
    added a commit that references this issue on Sep 14, 2023

    Merge pull request micropython#8345 from tannewt/s3_watchdog

    442f84d
  19. Taccart
    added a commit that references this issue on May 23, 2026

    esp32/machine_pwm: Always set the duty cycle when setting the frequency.

    c64a9ad
  20. jakub-vesely
    added a commit that references this issue on Sep 21, 2026

    esp32/machine_pwm: Always set the duty cycle when setting the frequency.

    4a116e9
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