libgpiod: The Modern Standard for GPIO Control on Raspberry Pi

With the deprecation of sysfs GPIO interfaces, libgpiod has emerged as the standard solution for GPIO control in modern Linux systems. As documented in Raspberry Pi's technical whitepaper [RP-006553-WP], libgpiod provides a robust, kernel-integrated approach to GPIO management.

Understanding libgpiod

libgpiod is a C library and toolkit for interacting with Linux GPIO character devices (/dev/gpiochipX). It's the recommended solution for production applications requiring GPIO control.

Version Considerations

There are two major versions of libgpiod:

• Version 1: Currently included in Raspberry Pi OS
• Version 2: Available but not yet default in Raspberry Pi OS

Raspberry Pi's Custom Kernel Modifications

State Persistence

Raspberry Pi has made special kernel modifications to make libgpiod more user-friendly:

1. Default Behavior

• Standard libgpiod releases revert GPIO states when programs exit
• Raspberry Pi's kernel maintains GPIO states after program termination

2. Configuration Options

• Add to config.txt: dtparam=strict_gpiod to enable standard behavior
• Or add to cmdline.txt: pinctrl_bcm2835.persist_gpio_outputs=n

Key Features

• Guaranteed GPIO line exclusivity
• Kernel-level access control
• Clean integration with Linux GPIO subsystem

Command-line Tools

Core Utilities:

gpiodetect    # List available GPIO chips
gpioinfo      # Display GPIO line information
gpioget       # Read GPIO values
gpioset       # Set GPIO values
gpiomon       # Monitor GPIO events
gpionotify    # Watch for GPIO changes
gpiofind      # Locate specific GPIO lines

Example Usage:

# List GPIO chips
gpiodetect

# Set GPIO output (Version 1)
gpioset --mode=wait gpiochip0 18=1

# Set GPIO output (Version 2)
gpioset gpiochip0 18=1

# Monitor GPIO changes
gpiomon gpiochip0 17

Programming with libgpiod

C Example:

#include 

struct gpiod_chip *chip;
struct gpiod_line *line;

// Open GPIO chip
chip = gpiod_chip_open("/dev/gpiochip0");

// Get GPIO line
line = gpiod_chip_get_line(chip, 18);

// Configure as output
gpiod_line_request_output(line, "my-led", 0);

// Set value
gpiod_line_set_value(line, 1);

Python Example (using gpiod module):

import gpiod

# Open chip
chip = gpiod.Chip('gpiochip0')

# Get line
line = chip.get_line(18)

# Configure as output
line.request(consumer="my-led", type=gpiod.LINE_REQ_DIR_OUT)

# Set value
line.set_value(1)

Best Practices

1. Error Handling

try:
    chip = gpiod.Chip('gpiochip0')
    line = chip.get_line(18)
except OSError as e:
    print(f"Failed to access GPIO: {e}")

2. Resource Management

with gpiod.Chip('gpiochip0') as chip:
    line = chip.get_line(18)
    with line.request(consumer="my-led",
                     type=gpiod.LINE_REQ_DIR_OUT) as requested_line:
        requested_line.set_value(1)

3. Event Handling

# Monitor GPIO events
with line.request(consumer="button",
                 type=gpiod.LINE_REQ_EV_BOTH_EDGES) as requested_line:
    while True:
        event = requested_line.event_wait(nsec=1000000000)
        if event:
            event_type = event.event_type
            timestamp = event.timestamp

Migration Tips

From sysfs:

# Old sysfs method
echo "18" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio18/direction
echo "1" > /sys/class/gpio/gpio18/value

# New libgpiod method
gpioset gpiochip0 18=1

From WiringPi/RPi.GPIO:

• Replace direct pin numbering with chip/line references
• Use libgpiod's event handling instead of polling
• Implement proper resource cleanup

Conclusion

libgpiod represents the future of GPIO control on Linux systems, including Raspberry Pi. With Raspberry Pi's kernel modifications for state persistence and the robust features provided by libgpiod, it offers a reliable and future-proof solution for GPIO control in production environments.

For detailed specifications and further reading, refer to the official Raspberry Pi GPIO whitepaper [RP-006553-WP] and the libgpiod documentation.