BananaPro/Pi: GPIO library

4. Test GPIO output (LED blink)

Physical setup: Connect LED anode (long leg) to GPIO pin via 220O resistor, cathode to GND.

# Find GPIO line number for your pin
# Example: Physical pin 7 is often PH2 (varies by board)
gpioinfo | grep PH2

# Set pin as output and turn on (replace gpiochip0 and line number)
gpioset gpiochip0 98=1  # Turn on (line 98 example, verify your board!)
sleep 1
gpioset gpiochip0 98=0  # Turn off

Simple blink script:

#!/bin/bash
CHIP=\"gpiochip0\"
LINE=\"98\"  # Change to your GPIO line number

for i in {1..10}; do
  gpioset $CHIP $LINE=1
  sleep 0.5
  gpioset $CHIP $LINE=0
  sleep 0.5
done

5. Test GPIO input (button read)

Physical setup: Connect one side of push button to GPIO pin, other side to GND. Enable internal pull-up or use external pull-up resistor (10kO to 3.3V).

# Read pin state (returns 0 or 1)
gpioget gpiochip0 98

# Monitor pin changes in real-time
gpiomon --num-events=10 gpiochip0 98
# Press button, watch for \"event\" lines

# Read with pull-up enabled (if kernel supports)
# Note: Not all kernels expose bias settings to gpioset
# May require Python gpiod library or kernel configuration

6. Python GPIO example

#!/usr/bin/env python3
import gpiod
import time

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

# Get GPIO line (change line number for your pin)
line = chip.get_line(98)

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

# Blink 10 times
for _ in range(10):
    line.set_value(1)
    time.sleep(0.5)
    line.set_value(0)
    time.sleep(0.5)

# Release line
line.release()

Concrete example (identify GPIO chips)

ls -l /dev/gpiochip*
gpioinfo 2>/dev/null | head -n 60

# Test specific pin (PH2 example - line 98 on many A20 boards)
gpioset gpiochip0 98=1  # LED on
sleep 1
gpioset gpiochip0 98=0  # LED off

Troubleshooting

Wrong pin toggles; unexpected behavior

• Symptoms: LED on wrong pin lights up; button input reads from different pin; multiple pins toggle together.
• Steps:
  1. Verify pin numbering scheme. Physical pin 7 ? GPIO 7 ? WiringPi pin 7. Use gpioinfo | grep PH to map Allwinner names to line numbers.
  2. Check board schematic or pinout diagram. Some pins have alternate functions (I2C, SPI) that may be active.
  3. Test with known-good pin: PH2 (often line 98) is usually safe for testing on Banana Pi/Pro.
  4. Disable conflicting services: systemctl status and check for SPI, I2C drivers claiming pins.
  5. Use gpioinfo to see which lines are marked \"used\" by kernel drivers.

Permission denied when accessing GPIO

• Symptoms: gpiodetect requires sudo; gpioset fails with \"Permission denied\"; /dev/gpiochip* owned by root.
• Steps:
  1. Check group membership: groups. Should include gpio or users.
  2. Add user to gpio group: sudo usermod -aG gpio $USER, then log out/in.
  3. Verify udev rules exist: ls /etc/udev/rules.d/*gpio*. Create 99-gpio.rules if missing (see step 3 above).
  4. Check /dev/gpiochip* permissions: ls -l /dev/gpiochip*. Should be crw-rw---- gpio or users group.
  5. Reload udev: sudo udevadm control --reload-rules && sudo udevadm trigger.

Pin conflicts with other services

• Symptoms: gpioinfo shows line \"used\"; gpioset fails with \"Device or resource busy\"; I2C/SPI not working after GPIO use.
• Steps:
  1. Check which driver is using the line: gpioinfo | grep used shows consumer name.
  2. Disable conflicting service: sudo systemctl stop i2c or blacklist kernel module.
  3. Choose different GPIO pin that's not claimed by hardware drivers.
  4. Check device tree overlays: Some images use overlays that pre-claim GPIO for specific functions.

No /dev/gpiochip* devices found

• Symptoms: ls /dev/gpiochip* returns \"No such file\"; gpiodetect shows nothing.
• Steps:
  1. Check kernel GPIO support: zcat /proc/config.gz | grep GPIO. Need CONFIG_GPIOLIB=y, CONFIG_GPIO_SYSFS=y or CONFIG_GPIO_CDEV=y.
  2. Verify kernel modules loaded: lsmod | grep gpio. Should see gpio_sunxi or similar.
  3. Try legacy sysfs interface: ls /sys/class/gpio. If present, kernel uses old interface (not recommended).
  4. Update kernel or switch to image with GPIO support enabled.

FAQ

Can I use 5V signals with Banana Pi GPIO?

No. Banana Pi GPIO pins are 3.3V only. Connecting 5V signal will damage the SoC. Use level shifter (bidirectional logic level converter) or voltage divider for 5V devices. Many I2C/SPI devices tolerate 3.3V even if powered by 5V.

What's the maximum current I can draw from a GPIO pin?

Safe continuous current: 4-6mA per pin. Absolute maximum: 10mA. Total for all GPIO pins: ~100mA. For loads >5mA (relays, motors, high-power LEDs), use transistor or MOSFET driver circuit powered from external 5V rail.

Which GPIO library should I use for new projects?

Use libgpiod (modern, kernel-supported). Avoid WiringPi (deprecated since 2019, unmaintained). Kernel sysfs interface (/sys/class/gpio) is deprecated but still works on older kernels. Python: python3-libgpiod. C/C++: libgpiod-dev.

How do I find GPIO line number for a physical pin?

Use board pinout diagram to find Allwinner port/pin (e.g., PH2), then gpioinfo | grep PH2 to get line number. No universal mapping; varies by kernel and device tree. Test with LED before connecting real hardware.

Can I use hardware PWM on GPIO pins?

Some A20 pins support hardware PWM (PWM0, PWM1 on specific pins). Check board schematic. Software PWM possible on any GPIO but has timing jitter (not suitable for precise motor control or servo). Use hardware PWM via /sys/class/pwm interface.

Why does WiringPi not work on my image?

WiringPi was deprecated in 2019 and removed from many modern distributions. If your image includes it, consider migrating to libgpiod. WiringPi may have incorrect pin mappings for newer kernels or board revisions.

How do I enable internal pull-up/pull-down resistors?

Depends on kernel and device tree configuration. libgpiod v2+ supports bias flags (LINE_REQ_FLAG_BIAS_PULL_UP). Older kernels require device tree modification. For reliability, use external pull-up/pull-down resistors (10kO).

Can I use interrupts to detect button presses?

Yes. Use gpiomon for command-line monitoring, or Python libgpiod with event_wait() for edge detection (rising, falling, both). More efficient than polling. Requires kernel interrupt support for GPIO lines.

External reference

• libgpiod documentation
• Linux Kernel GPIO documentation
• linux-sunxi GPIO documentation (Allwinner-specific)

Related pages

• WiringPi (deprecated, archival)
• LeMaker Banana Pro / Pi (board hub)
• Main Page

Author: LeMaker Documentation Team
Last updated: 2026-01-11