README

rpi-lgpio is a compatibility package intended to provide compatibility with the rpi-gpio (aka RPi.GPIO) library, on top of kernels that only support the gpiochip device (and which have removed the deprecated sysfs GPIO interface).

Warning

You cannot install rpi-lgpio and rpi-gpio (aka RPi.GPIO, the library it emulates) at the same time, in the same Python environment. Both packages attempt to install a module named RPi.GPIO and obviously this will not work.

Contents

Installation

rpi-lgpio is distributed in several formats. The following sections detail installation from a variety of formats. But first a warning:

Warning

You cannot install rpi-lgpio and rpi-gpio (aka RPi.GPIO, the library it emulates) at the same time, in the same Python environment. Both packages attempt to install a module named RPi.GPIO and obviously this will not work.

apt/deb package

If your distribution includes rpi-lgpio in its archive of apt packages, then you can simply:

$ sudo apt remove python3-rpi.gpio
$ sudo apt install python3-rpi-lgpio

If you wish to go back to rpi-gpio:

$ sudo apt remove python3-rpi-lgpio
$ sudo apt install python3-rpi.gpio

wheel package

If your distribution does not include a “native” packaging of rpi-lgpio, you can also install using pip (preferably in a Python virtual environment):

$ pip uninstall rpi-gpio
$ pip install rpi-lgpio

On some platforms you may need to use a Python 3 specific alias of pip:

$ pip3 uninstall rpi-gpio
$ pip3 install rpi-lgpio

The instructions above assume that rpi-gpio is already installed by pip as well, but this may not be the case. For instance, you may have rpi-gpio installed from, say, apt, but your particular distro doesn’t also include rpi-lgpio. In this case you may need to remove rpi-gpio from apt first:

$ sudo apt remove python3-rpi.gpio
$ pip3 install rpi-lgpio

If you wish to install system-wide with pip, you may need to place sudo in front of the pip (or pip3) commands too. Please be aware that on modern versions of pip you will need to explicitly accept the risk of trying to co-exist apt and pip packages as follows:

$ sudo pip3 install --break-system-packages rpi-lgpio

Differences

Many of the assumptions underlying RPi.GPIO – that it has complete access to, and control over, the registers controlling the GPIO pins – do not work when applied to the Linux gpiochip devices. To that end, while the library strives as far as possible to be “bug compatible” with RPi.GPIO, there are differences in behaviour that may result in incompatibility.

Bug Compatible?

What does being “bug compatible” mean? It is not enough for the library to implement the RPi.GPIO API. It must also:

  • Act, as far as possible, in the same way to the same calls with the same values

  • Raise the same exception types, with the same messages, in the same circumstances

  • Break (i.e. fail to operate correctly) in the same way, as far as possible

This last point may sound silly, but a library is always used in unexpected or undocumented ways by some applications. Thus anything that tries to take the place of that library must do more than simply operate the same as the “documented surface” would suggest.

That said, given that the underlying assumptions are fundamentally different this will not always be possible…

Pi Revision

The RPi.GPIO module attempts to determine the model and revision of Raspberry Pi board that it is running on when the module is imported, raising RuntimeError at import time if it finds it is not running on a Raspberry Pi. rpi-lgpio emulates this behaviour, but this can be inconvenient for certain situations including testing, but also usage of rpi-lgpio on other single board computers.

To that end rpi-lgpio permits a Raspberry Pi revision code to be manually specified via the environment in the RPI_LGPIO_REVISION value. For example:

$ RPI_LGPIO_REVISION='c03114' python3
Python 3.10.6 (main, Aug 10 2022, 11:40:04) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from RPi import GPIO
>>> GPIO.RPI_INFO
{'P1_REVISION': 3, 'REVISION': 'c03114', 'TYPE': 'Pi 4 Model B',
'MANUFACTURER': 'Sony UK', 'PROCESSOR': 'BCM2711', 'RAM': '4GB'}
>>> exit()
$ RPI_LGPIO_REVISION='902120' python3
Python 3.10.6 (main, Aug 10 2022, 11:40:04) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from RPi import GPIO
>>> GPIO.RPI_INFO
{'P1_REVISION': 3, 'REVISION': '902120', 'TYPE': 'Zero 2 W',
'MANUFACTURER': 'Sony UK', 'PROCESSOR': 'BCM2837', 'RAM': '512M'}
>>> exit()

GPIO Chip

The lgpio library needs to know the number of the /dev/gpiochip device it should open. By default this will be calculated from the reported Pi Revision (which may be customized as detailed in that section). In practice this means the chip defaults to “4” on the Raspberry Pi Model 5B, and “0” on all other boards.

You may also specify the chip manually using the RPI_LGPIO_CHIP environment variable. For example:

$ ls /dev/gpiochip*
crw-------  1 root root    254, 0 Oct  1 15:00 /dev/gpiochip0
crw-------  1 root root    254, 1 Oct  1 15:00 /dev/gpiochip1
crw-------  1 root root    254, 2 Oct  1 15:00 /dev/gpiochip2
crw-------  1 root root    254, 3 Oct  1 15:00 /dev/gpiochip3
crw-rw----+ 1 root dialout 254, 4 Oct  1 15:00 /dev/gpiochip4
crw-------  1 root root    254, 5 Oct  1 15:00 /dev/gpiochip5
$ RPI_LGPIO_CHIP=5 python3
Python 3.11.5 (main, Aug 29 2023, 15:31:31) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from RPi import GPIO
>>> GPIO.setmode(GPIO.BCM)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/RPi/GPIO/__init__.py", line 513, in setmode
    _chip = _check(lgpio.gpiochip_open(int(chip_num)))
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/lgpio.py", line 645, in gpiochip_open
    return _u2i(handle)
           ^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/lgpio.py", line 458, in _u2i
    raise error(error_text(v))
lgpio.error: 'can not open gpiochip'

This is primarily useful for other boards where the correct gpiochip device is something other than 0.

Alternate Pin Modes

The gpio_function() function can be used to report the current mode of a pin. In RPi.GPIO this may return several “alternate” mode values including SPI, I2C, and HARD_PWM. rpi-lgpio will only ever return the basic IN and OUT values however, as the underlying gpiochip device cannot report alternate modes.

For example, under RPi.GPIO:

>>> from RPi import GPIO
>>> GPIO.setmode(GPIO.BCM)
>>> GPIO.gpio_function(2) == GPIO.I2C
True

Under rpi-lgpio:

>>> from RPi import GPIO
>>> GPIO.setmode(GPIO.BCM)
>>> GPIO.gpio_function(2) == GPIO.I2C
False
>>> GPIO.gpio_function(2) == GPIO.IN
True

Stack Traces

While every effort has been made to raise the same exceptions with the same messages as RPi.GPIO, rpi-lgpio does raise the exceptions from pure Python so the exceptions will generally include a larger stack trace than under RPi.GPIO. For example, under RPi.GPIO:

>>> from RPi import GPIO
>>> GPIO.setmode(GPIO.BCM)
>>> GPIO.setup(26, GPIO.IN)
>>> GPIO.output(26, 1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: The GPIO channel has not been set up as an OUTPUT

Under rpi-lgpio:

>>> from RPi import GPIO
>>> GPIO.setmode(GPIO.BCM)
>>> GPIO.setup(26, GPIO.IN)
>>> GPIO.output(26, 1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/dave/projects/rpi-lgpio/rpi-lgpio/RPi/GPIO.py", line 626, in output
    _check_output(mode, 'The GPIO channel has not been set up as an OUTPUT')
  File "/home/dave/projects/rpi-lgpio/rpi-lgpio/RPi/GPIO.py", line 242, in _check_output
    raise RuntimeError(msg)
RuntimeError: The GPIO channel has not been set up as an OUTPUT

Simultaneous Access

Two processes using RPi.GPIO can happily control the same pin. This is simply not permitted by the Linux gpiochip device and will fail under rpi-lgpio. For example, if another process has reserved GPIO26, and our script also tries to allocate it:

>>> from RPi import GPIO
>>> GPIO.setmode(GPIO.BCM)
>>> GPIO.setup(26, GPIO.OUT)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/dave/projects/rpi-lgpio/rpi-lgpio/RPi/GPIO.py", line 569, in setup
    initial = _check(lgpio.gpio_read(_chip, gpio))
  File "/home/dave/envs/rpi-lgpio/lib/python3.10/site-packages/lgpio.py", line 894, in gpio_read
    return _u2i(_lgpio._gpio_read(handle&0xffff, gpio))
  File "/home/dave/envs/rpi-lgpio/lib/python3.10/site-packages/lgpio.py", line 461, in _u2i
    raise error(error_text(v))
lgpio.error: 'GPIO not allocated'

Debounce

Debouncing of signals works fundamentally differently in RPi.GPIO, and in lgpio (the library underlying rpi-lgpio). Rather than attempt to add more complexity in between users and lgpio, which would also inevitably slow down edge detection (with all the attendant timing issues for certain applications) it is likely preferable to just live with this difference, but document it thoroughly.

RPi.GPIO debounces signals by tracking the last timestamp at which it saw a specified edge and suppressing reports of edges that occur within the specified number of milliseconds after that.

lgpio (and thus rpi-lgpio) debounces by waiting for a signal to be stable for the specified number of milliseconds before reporting the edge.

For some applications, there will be little/no difference other than rpi-lgpio reporting an edge a few milliseconds later than RPi.GPIO would (specifically, by the amount of debounce requsted). The following diagram shows the waveform from a “bouncy” switch being pressed once, along with the positions in time where RPi.GPIO and rpi-lgpio would report the rising edge when debounce of 3ms is requested:

 0ms    2ms     4ms     6ms     8ms
 |      |       |       |       |
 |      ┌─┐ ┌─┐ ┌─────────────────┐
 |      │ │ │ │ │           :     │
 |      │ │ │ │ │           :     │
 ───────┘ └─┘ └─┘           :     └────────────────────────
        :                   :
        :                   :
     RPi.GPIO             rpi-lgpio

RPi.GPIO reports the edge at 2ms, then suppresses the edges at 3ms and 4ms because they are within 3ms of the last edge. By contrast, rpi-lgpio ignores the first and second rising edges (because they didn’t stay stable for 3ms) and only reports the third edge at 7ms (after it’s spent 3ms stable).

However, consider this same scenario if debounce of 2ms is requested:

 0ms    2ms     4ms     6ms     8ms
 |      |       |       |       |
 |      ┌─┐ ┌─┐ ┌─────────────────┐
 |      │ │ │ │ │       :         │
 |      │ │ │ │ │       :         │
 ───────┘ └─┘ └─┘       :         └────────────────────────
        :       :       :
        :       :       :
    RPi.GPIO  RPi.GPIO  rpi-lgpio

In this case, RPi.GPIO reports the switch twice because the third edge is still 2ms after the first edge. However, rpi-lgpio only reports the switch once because only one edge stayed stable for 2ms. Also note in this case, that rpi-lgpio’s report time has moved back to 6ms because it’s not waiting as long for stability.

This implies that you may find shorter debounce periods preferable when working with rpi-lgpio, than with RPi.GPIO. They will still debounce effectively, but will reduce the delay in reporting edges.

One final scenario to consider is a waveform of equally spaced, repeating pulses (like PWM) every 2ms:

 0ms    2ms     4ms     6ms     8ms     10ms    12ms
 |      |       |       |       |       |       |
 |      ┌────┐  ┌────┐  ┌────┐  ┌────┐  ┌────┐  ┌────┐  ┌──
 |      │    │  │    │  │    │  │    │  │    │  │    │  │
 |      │    │  │    │  │    │  │    │  │    │  │    │  │
 ───────┘    └──┘    └──┘    └──┘    └──┘    └──┘    └──┘
        :               :               :               :
        :               :               :               :
   RPi.GPIO        RPi.GPIO        RPi.GPIO        RPi.GPIO

If we request rising edge detection with a debounce of 3ms, RPi.GPIO reports half of the edges; it’s suppressing every other edge as they occur within 3ms of the edge preceding them. rpi-lgpio, on the other hand, reports no edges at all because none of them stay stable for 3ms.

PWM on inputs

RPi.GPIO (probably erroneously) permits PWM objects to continue operating on pins that are switched to inputs:

>>> from RPi import GPIO
>>> GPIO.setmode(GPIO.BCM)
>>> GPIO.setup(26, GPIO.OUT)
>>> p = GPIO.PWM(26, 1000)
>>> p.start(75)
>>> GPIO.setup(26, GPIO.IN)
>>> p.stop()
>>> p.start(75)
>>> p.stop()

This will not work under rpi-lgpio:

>>> from RPi import GPIO
>>> GPIO.setmode(GPIO.BCM)
>>> GPIO.setup(26, GPIO.OUT)
>>> p = GPIO.PWM(26, 1000)
>>> p.start(75)
>>> GPIO.setup(26, GPIO.IN)
>>> p.stop()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/dave/projects/rpi-lgpio/rpi-lgpio/RPi/GPIO.py", line 190, in stop
    lgpio.tx_pwm(_chip, self._gpio, 0, 0)
  File "/home/dave/envs/rpi-lgpio/lib/python3.10/site-packages/lgpio.py", line 1074, in tx_pwm
    return _u2i(_lgpio._tx_pwm(
  File "/home/dave/envs/rpi-lgpio/lib/python3.10/site-packages/lgpio.py", line 461, in _u2i
    raise error(error_text(v))
lgpio.error: 'bad PWM micros'

Though note that the error occurs when the PWM object is next acted upon, rather than at the point when the GPIO is switched to an input.

API Reference

The API of rpi-lgpio (naturally) follows that of rpi-gpio (aka RPi.GPIO) as closely as possible. As such the following is simply a re-iteration of that API.

Initialization

RPi.GPIO.setmode(new_mode)[source]

Set up the numbering mode to use for the pins on the board. The options for new_mode are:

  • BOARD - Use Raspberry Pi board numbers

  • BCM - Use Broadcom GPIO 00..nn numbers

If a numbering mode has already been set, and new_mode is not the same as the result of getmode(), a ValueError is raised.

Parameters:

new_mode (int) – The new numbering mode to apply

RPi.GPIO.getmode()[source]

Get the numbering mode used for the pins on the board. Returns BOARD, BCM or None.

RPi.GPIO.setup(chanlist, direction, pull_up_down=20, initial=None)[source]

Set up a GPIO channel or iterable of channels with a direction and (optionally, for inputs) pull/up down control, or (optionally, for outputs) and initial state.

The GPIOs to affect are listed in chanlist which may be any iterable. The direction is either IN or OUT.

If direction is IN, then pull_up_down may specify one of the values PUD_UP to set the internal pull-up resistor, PUD_DOWN to set the internal pull-down resistor, or the default PUD_OFF which disables the internal pulls.

If direction is OUT, then initial may specify zero or one to indicate the initial state of the output.

Parameters:

  • chanlist (list or tuple or int) – The list of GPIO channels to setup

  • direction (int) – Whether the channels should act as inputs or outputs

  • pull_up_down (int or None) – The internal pull resistor (if any) to enable for inputs

  • initial (bool or int or None) – The initial state of an output

RPi.GPIO.cleanup(chanlist=None)[source]

Reset the specified GPIO channels (or all channels if none are specified) to INPUT with no pull-up / pull-down and no event detection.

Parameters:

chanlist (list or tuple or int or None) – The channel, or channels to clean up

Pin Usage

RPi.GPIO.input(channel)[source]

Input from a GPIO channel. Returns 1 or 0.

This can also be called on a GPIO output, in which case the value returned will be the last state set on the GPIO.

Parameters:

channel (int) – The board pin number or BCM number depending on setmode()

RPi.GPIO.output(channel, value)[source]

Output to a GPIO channel or list of channels. The value can be the integer LOW or HIGH, or a list of integers.

If a list of channels is specified, with a single integer for the value then it is applied to all channels. Otherwise, the length of the two lists must match.

Parameters:

  • channel (list or tuple or int) – The GPIO channel, or list of GPIO channels to output to

  • value (list or tuple or int) – The value, or list of values to output

Edge Detection

RPi.GPIO.wait_for_edge(channel, edge, bouncetime=None, timeout=None)[source]

Wait for an edge on the specified channel. Returns channel or None if timeout elapses before the specified edge occurs.

Note

Debounce works significantly differently in rpi-lgpio than it does in rpi-gpio; please see Debounce for more information on the differences.

Parameters:

  • channel (int) – The board pin number or BCM number depending on setmode() to watch for changes

  • edge (int) – One of the constants RISING, FALLING, or BOTH

  • bouncetime (int or None) – Time (in ms) used to debounce signals

  • timeout (int or None) – Maximum time (in ms) to wait for the edge

RPi.GPIO.add_event_detect(channel, edge, callback=None, bouncetime=None)[source]

Start background edge detection on the specified GPIO channel.

If callback is specified, it must be a callable that will be executed when the specified edge is seen on the GPIO channel. The callable must accept a single parameter: the channel on which the edge was detected.

Note

Debounce works significantly differently in rpi-lgpio than it does in rpi-gpio; please see Debounce for more information on the differences.

Parameters:

  • channel (int) – The board pin number or BCM number depending on setmode() to watch for changes

  • edge (int) – One of the constants RISING, FALLING, or BOTH

  • callback (callable or None) – The callback to run when an edge is detected; must take a single integer parameter of the channel on which the edge was detected

  • bouncetime (int or None) – Time (in ms) used to debounce signals

RPi.GPIO.add_event_callback(channel, callback)[source]

Add a callback to the specified GPIO channel which must already have been set for background edge detection with add_event_detect().

Parameters:

  • channel (int) – The board pin number or BCM number depending on setmode() to watch for changes

  • callback – The callback to run when an edge is detected; must take a single integer parameter of the channel on which the edge was detected

RPi.GPIO.event_detected(channel)[source]

Returns True if an edge has occurred on the specified channel since the last query of the channel (if any). Querying this will also reset the internal edge detected flag for this channel.

The channel must previously have had edge detection enabled with add_event_detect().

Parameters:

channel (int) – The board pin number or BCM number depending on setmode()

Miscellaneous

RPi.GPIO.gpio_function(channel)[source]

Return the current GPIO function (IN, OUT, HARD_PWM, SERIAL, I2C, SPI) for the specified channel.

Note

This function will only return IN or OUT under rpi-lgpio as the underlying kernel device cannot report the alt-mode of GPIO pins.

Parameters:

channel (int) – The board pin number or BCM number depending on setmode()

RPi.GPIO.setwarnings(value)[source]

Enable or disable warning messages. These are mostly produced when calling setup() or cleanup() to change channel modes.

PWM

class RPi.GPIO.PWM(channel, frequency)[source]

Initializes and controls software-based PWM (Pulse Width Modulation) on the specified channel at frequency (in Hz).

Call start() and stop() to generate and stop the actual output respectively. ChangeFrequency() and ChangeDutyCycle() can also be used to control the output.

Note

Letting the PWM object go out of scope (and be garbage collected) will implicitly stop the PWM.

ChangeDutyCycle(dc)[source]

Changes the duty cycle (percentage of the time that the pin is “on”) to dc.

ChangeFrequency(frequency)[source]

Changes the frequency of rising edges output by the pin.

start(dc)[source]

Starts outputting a wave on the assigned pin with a duty-cycle (which must be between 0 and 100) given by dc.

Parameters:

dc (float) – The duty-cycle (the percentage of time the pin is “on”)

stop()[source]

Stops outputting a wave on the assigned pin, and sets the pin’s state to off.

Constants

RPi.GPIO.RPI_INFO

A dictionary that provides information about the model of Raspberry Pi that the library is loaded onto. Includes the following keys:

P1_REVISION

The revision of the P1 header. 0 indicates no P1 header (typical on the compute module range), 1 and 2 vary on the oldest Raspberry Pi models, and 3 is the typical 40-pin header present on all modern Raspberry Pis.

REVISION

The hex board revision code as a str.

TYPE

The name of the Pi model, e.g. “Pi 4 Model B”

MANUFACTURER

The name of the board manufacturer, e.g. “Sony UK”

PROCESSOR

The name of the SoC used on the board, e.g. “BCM2711”

RAM

The amount of RAM installed on the board, e.g. “4GB”

The board revision can be overridden with the RPI_LGPIO_REVISION environment variable; see Pi Revision for further details.

RPi.GPIO.RPI_REVISION

The same as the P1_REVISION key in RPI_INFO

RPi.GPIO.BOARD

Indicates to setmode() that physical board numbering is requested

RPi.GPIO.BCM

Indicates to setmode() that GPIO numbering is requested

RPi.GPIO.PUD_OFF

Used with setup() to disable internal pull resistors on an input

RPi.GPIO.PUD_DOWN

Used with setup() to enable the internal pull-down resistor on an input

RPi.GPIO.PUD_UP

Used with setup() to enable the internal pull-up resistor on an input

RPi.GPIO.OUT

Used with setup() to set a GPIO to an output, and gpio_function() to report a GPIO is an output

RPi.GPIO.IN

Used with setup() to set a GPIO to an input, and gpio_function() to report a GPIO is an input

RPi.GPIO.HARD_PWM
RPi.GPIO.SERIAL
RPi.GPIO.I2C
RPi.GPIO.SPI

Used with gpio_function() to indicate “alternate” modes of certain GPIO pins.

Note

In rpi-lgpio these values will never be returned as the kernel device cannot report if pins are in alternate modes.

RPi.GPIO.LOW = 0

Used with output() to turn an output GPIO off

RPi.GPIO.HIGH = 1

Used with output() to turn an output GPIO on

RPi.GPIO.RISING

Used with wait_for_edge() and add_event_detect() to specify that rising edges only should be sampled

RPi.GPIO.FALLING

Used with wait_for_edge() and add_event_detect() to specify that falling edges only should be sampled

RPi.GPIO.BOTH

Used with wait_for_edge() and add_event_detect() to specify that all edges should be sampled

Changelog

Release 0.4 (2023-10-03)

  • Add compatibility with Raspberry Pi 5 (auto-selection of correct gpiochip device)

  • Add ability to override gpiochip selection; see GPIO Chip

  • Convert bouncetime -666 to None (bug compatibility, which also ensures this should work with GPIO Zero’s rpigpio pin driver)

  • Fix pull_up_down default on setup()

  • Fix changing pull_up_down of already-acquired input

  • Ensure PWM.stop() is idempotent

Release 0.3 (2022-10-14)

Release 0.2 (2022-10-14)

Release 0.1 (2022-10-14)

  • Initial release

License

The MIT License (MIT)

Copyright (c) 2022 Dave Jones

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Indexes