8000 Reading the value of an output pin behaves differently in ESP32S2 than in SAMD · Issue #3353 · adafruit/circuitpython · GitHub
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Reading the value of an output pin behaves differently in ESP32S2 than in SAMD #3353

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anecdata opened this issue Aug 30, 2020 · 2 comments · Fixed by #3495
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Reading the value of an output pin behaves differently in ESP32S2 than in SAMD #3353

anecdata opened this issue Aug 30, 2020 · 2 comments · Fixed by #3495
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bug espressif applies to multiple Espressif chips good first issue
Milestone
6.x.x - Bug Fixes

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@anecdata
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anecdata commented Aug 30, 2020 •
edited
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Is this a bug, or is it explicitly undefined behavior to read the value of an output?

>>> import board
>>> from digitalio import DigitalInOut, Direction
>>> led = DigitalInOut(any_gpio)
>>> led.direction = Direction.OUTPUT

PyPortal (alpha.3):

>>> led.value = True
>>> led.value
True

(the LED is ON)

vs.

Saola (alpha.3):

>>> led.value = True
>>> led.value
False

(the LED is ON)

[edited to explicitly show pin is set up in either case as an output]
@jepler
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jepler commented Aug 30, 2020

If it's not intended to be able to read back the value previously set on an output pin, accessing the value property to read it should give an exception.

I think the problem arises because the esp-idf defines the return value of this routine in a surprising way, rather than returning the value currently driven onto the pin:

 * @brief  GPIO get input level
 *
 * @warning If the pad is not configured for input (or input and output) the returned value is always 0.
 *
 * @param  hw Peripheral GPIO hardware instance address.
 * @param  gpio_num GPIO number. If you want to get the logic level of e.g. pin GPIO16, gpio_num should be GPIO_NUM_16 (16);
 *
 * @return
 *     - 0 the GPIO input level is 0
 *     - 1 the GPIO input level is 1

@anecdata
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anecdata commented Aug 30, 2020 •
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FWIW, input behaves the same on both. It's conceptually an easier case to make that it's an error since the value is controlled by an external source:

>>> pin = DigitalInOut(any_gpio)
>>> pin.direction = Direction.INPUT
>>> pin.value
False
>>> pin.value = True
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: Cannot set value when direction is input.

addendum...

analog outputs don't allow reading the value:

>>> import board
>>> from analogio import AnalogOut
>>> a = AnalogOut(board.A0)
>>> a.value
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: unreadable attribute

@dhalbert dhalbert added the espressif applies to multiple Espressif chips label Aug 31, 2020
@dhalbert dhalbert added this to the 6.x.x - Bug Fixes milestone Aug 31, 2020
@tannewt tannewt mentioned this issue Sep 30, 2020
Merged
tannewt added a commit that referenced this issue Oct 1, 2020
@tannewt
Add Metro ESP32S2
a739d31 
Also fix two bugs:
* Crash when resetting board.SPI when it hasn't been inited.
* Reading back the output value is always false. Fixes #3353
@anecdata anecdata mentioned this issue Sep 29, 2022
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Add Metro ESP32S2 tannewt/circuitpython
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