Use micros() instead of cycle counting. #93
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In the ESP32 Arduino library, noInterrupts() is a nop, so interrupts still occur while receiving a value. On my board there is at least one interrupt every time we try to read a value, which messes up the reading. Instead of counting cycles, use micros() to keep track of time. This increases the success rate of receiving data to 90% or so. A better fix would be to implement noInterrupts() for the ESP32, but that looks a lot harder. The new code path is probably not suitable for slower micros, but hopefully those use the __AVR code path anyway.
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use of micro() while interrupts are disabled leads to unexpected beviour on
some boards. if interrupts are disabled, the clock stops ticking after a
while... then... we're when and where it becomes unexpected trapped in
a task that rely on the clock.
…On 12 November 2017 at 20:12, Tim Newsome ***@***.***> wrote:
In the ESP32 Arduino library, noInterrupts() is a nop, so interrupts
still occur while receiving a value. On my board there is at least one
interrupt every time we try to read a value, which messes up the
reading. Instead of counting cycles, use micros() to keep track of time.
This increases the success rate of receiving data to 90% or so.
A better fix would be to implement noInterrupts() for the ESP32, but
that looks a lot harder. The new code path is probably not suitable for
slower micros, but hopefully those use the __AVR code path anyway.
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#93
Commit Summary
- Use micros() instead of cycle counting.
File Changes
- *M* DHT.cpp
<https://github.com/adafruit/DHT-sensor-library/pull/93/files#diff-0>
(21)
- *M* DHT.h
<https://github.com/adafruit/DHT-sensor-library/pull/93/files#diff-1>
(2)
Patch Links:
- https://github.com/adafruit/DHT-sensor-library/pull/93.patch
- https://github.com/adafruit/DHT-sensor-library/pull/93.diff
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@khjoen, that's good to know! So this code must definitely not be merged. It's working for me because interrupts aren't actually being disabled, but that is really the bug that should be fixed. |
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I can confirm the same issues using an ESP-WROOM-32. The changes in this branch solved them. Issues with unmodified code: I connected the DHT22 to pin 15 of the ESP32 and its 3.3V pin, using a 10k pullup resistor between data and 3.3V. I'm using the Arduino IDE to upload. My sketch consists of the basic DHT example. The data is read fine from the sensor. The checksum is consistently read incorrectly though. Example output of received data: In all of these readouts, the checksum read from the sensor (e.g. How I solved it:
I guess that although the changes cannot be merged as is, it would be great if these could be supplied as an option to the constructor. |
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Not sure if it helps, but you can take a look at https://github.com/beegee-tokyo/DHTesp/blob/master/DHTesp.cpp and see how it does the 'stop task switching' on esp32. |
In the ESP32 Arduino library, noInterrupts() is a nop, so interrupts
still occur while receiving a value. On my board there is at least one
interrupt every time we try to read a value, which messes up the
reading. Instead of counting cycles, use micros() to keep track of time.
This increases the success rate of receiving data to 90% or so.
A better fix would be to implement noInterrupts() for the ESP32, but
that looks a lot harder. The new code path is probably not suitable for
slower micros, but hopefully those use the __AVR code path anyway.
Thank you for creating a pull request to contribute to Adafruit's GitHub code!
Before you open the request please review the following guidelines and tips to
help it be more easily integrated:
I'm not sure this should be merged as-is, but I want it to be available to people who are running into the same problem.