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i2cioexpander inconsistencies and problems

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Evaluación

Dificultad
4/5
Tiempo estimado
3-5 días
Aptitud para principiantes
45/100
Tipo de issue
Error
Claridad
Bastante claro
Estado de actividad
Tranquilo
Stack tecnológico
c
Área
embedded-iot

Línea de trabajo

Start by reading reset_board_buses() in shared-module/board/__init__.c and compare its behavior with common_hal_i2cioexpander_ioexpander_construct() and common_hal_i2cdisplaybus_i2cdisplaybus_construct(). Then trace the CIRCUITPY_I2CIOEXPANDER defaults across ports. Done means the intended bus and pin reset behavior is consistent, including for external I2C devices and user-created expanders.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

bug digitalio
CircuitPython version and board name
main
Code/REPL
n.a.
Behavior

There are a number of inconsistencies across ports regarding the i2cioexpander module. Also, the behavior is not as intended:

  1. CIRCUITPY_I2CIOEXPANDER defaults to 0 for all ports except raspberrypi. That port sets the value to =1 (instead of ?=1), so it is impossible to override it in a mpconfigboard.mk file. While this sounds like just another module for the raspberrypi port, it also changes behavior as a side effect. Setting CIRCUITPY_I2CIOEXPANDER prevents resetting the board I2C bus (see reset_board_buses() in shared-module/board/__init__.c. So none of the raspberrypi boards reset the board I2C bus, while all espressif boards except the yotas do the reset.
  2. The coding in reset_board_buses() has two additional problems. It silently assumes that the ioexpander is an internal peripheral and not just a normal external i2c device. This assumption can be wrong.
  3. Major problem: not resetting the bus in this way does not prevent resetting the SCL/SDA pins. So although the bus is not explicitely reset, it is still unusable after the cleanup routines from main.c.

(1) is easy to solve.
(2) is debateble: treating ioexpanders as something special is possible, but the current implementation treats them differently if they are not on the board I2C bus.
(3) common_hal_i2cioexpander_ioexpander_construct() could call common_hal_busio_i2c_never_reset(), like common_hal_i2cdisplaybus_i2cdisplaybus_construct() does. As an alternative, this can be added to all boards that create an ioexpander and treat all ioexpander instances created from user code as "normal" i2c devices.

Description

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Additional information

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Lenguaje dominante
C
Estrellas
4.6k
Forks
1.4k
Merge medio
1 d 8 h
PR fusionados (30 d)
155

Preparar el entorno

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Primeros pasos

  1. Lee el issue completo y luego la guía de contribución del proyecto.
  2. Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

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