QUERY · ISSUE

ESP8266: PWM glitches when doing DHT measure

openby EddieParisopened 2021-02-21updated 2022-03-30

port-esp8266

When using a PWM channel in parallel of a DHT measure, there can be some glitches on the PWM channel at the measure time. This is because the DHT drivers locks interrupts for accurate protocol timing handling, and the PWM driver relies on these interrupts.

CANDIDATE · ISSUE

ESP8266: PWM glitches on a channel when setting duty on another one (ESP8266)

closedby EddieParisopened 2020-04-24updated 2020-06-10

port-esp8266

When having a PWM channel set on and changing the PWM duty on another channel, the first channel experiences glitches.

This is very visible when driving leds.

This is due to software PWM handling, the toggle between the current timing scheme and the prepared timing scheme can occur anytime.

Solution is to move the switch inside the interrupt when the last timer of the cycle occurs.

Assessment

Q Qwen · high

Both issues report PWM glitches on the ESP8266 port, but they describe different root causes and scenarios. Issue #6945 is about PWM glitches caused by the DHT driver disabling interrupts during measurement, affecting PWM channels that rely on those interrupts. Issue #5965 is about PWM glitches occurring when changing duty cycle on one channel affecting another channel due to unsynchronized timing scheme switching in the software PWM implementation. While both involve PWM glitches on ESP8266, the underlying mechanisms and triggers are distinct. The fix for #5965 (moving timing switch inside interrupt) would not address the interrupt masking issue described in #6945.

Suggested action

Keep both issues open as they address different problems. The maintainer may want to review if there's a common underlying interrupt handling issue that could be addressed, but the specific fixes required are different for each case.

ESP8266: PWM glitches when doing DHT measure

ESP8266: PWM glitches on a channel when setting duty on another one (ESP8266)

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