CM5 GPIO

General Purpose I/O — Hardware & Software Guide

Platform	Raspberry Pi CM5
OS	Ubuntu 24.04 LTS
Connector	SM10B-GHS (10-pin)

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Hardware Overview

The CM GPIO port is a 10-pin JST GH connector (SM10B-GHS) on the Lectron PI5 Autopilot board. It exposes six general-purpose I/O lines from the Raspberry Pi CM5, a 5 V power supply pin, and a ground reference. Pins 8 and 9 carry UART2 TX/RX and are not covered in this document.

Board Photos

The image below shows the CM GPIO connector with an LED test harness connected.

The connector is located on the board side panel:

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Pin Assignment

The table below lists all 10 pins of the CM GPIO connector. The six GPIO pins are the focus of this document.

Pin	Signal	Voltage	Direction	Notes
1	SYSTEM 5V	+5V	Power	Board supply voltage
2	CM5 GPIO22	+3.3V	I/O	General purpose I/O
3	CM5 GPIO23	+3.3V	I/O	General purpose I/O
4	CM5 GPIO24	+3.3V	I/O	General purpose I/O
5	CM5 GPIO25	+3.3V	I/O	General purpose I/O
6	CM5 GPIO26	+3.3V	I/O	General purpose I/O
7	CM5 GPIO27	+3.3V	I/O	General purpose I/O
8	CM5 UART2 TX	+3.3V	Output	UART2 transmit (not covered here)
9	CM5 UART2 RX	+3.3V	Input	UART2 receive (not covered here)
10	GROUND	GND	Power	Common ground reference

UART2 Pins

Pins 8 and 9 (UART2 TX/RX) share the same connector but are documented separately in the UART interface guide.

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Linux GPIO Interface

GPIO Chip

On Ubuntu 24.04 with the CM5, the main RP1 GPIO controller is exposed as gpiochip4. This is the chip that controls GPIO22–GPIO27.

$ sudo gpiodetect
gpiochip0 [gpio-brcmstb@107d508500] (32 lines)
gpiochip1 [gpio-brcmstb@107d508520] (4 lines)
gpiochip2 [gpio-brcmstb@107d517c00] (15 lines)
gpiochip3 [gpio-brcmstb@107d517c20] (6 lines)
gpiochip4 [pinctrl-rp1] (54 lines)    <-- this one

Verify GPIO Lines

Confirm GPIO22–27 are available and unused:

$ sudo gpioinfo gpiochip4 | grep -E 'GPIO2[2-7]'
line  22: "GPIO22"  unused  input  active-high
line  23: "GPIO23"  unused  input  active-high
line  24: "GPIO24"  unused  input  active-high
line  25: "GPIO25"  unused  input  active-high
line  26: "GPIO26"  unused  input  active-high
line  27: "GPIO27"  unused  input  active-high

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Command-Line Usage (gpiod)

The gpiod package is pre-installed on Ubuntu 24.04. All commands require sudo.

Set a Single Pin HIGH

# Drive GPIO22 HIGH for 3 seconds
sudo gpioset --mode=time -s 3 gpiochip4 22=1

Set All GPIO Pins HIGH

# Drive all six GPIO pins HIGH for 5 seconds
sudo gpioset --mode=time -s 5 gpiochip4 22=1 23=1 24=1 25=1 26=1 27=1

Read a Pin State

# Read the current state of GPIO22
sudo gpioget gpiochip4 22

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C Programming Example

The following C program uses the Linux kernel's gpio.h interface directly via ioctl — no additional libraries are required beyond standard Linux headers.

Build

gcc -o gpio_led_test gpio_led_test.c
sudo ./gpio_led_test

Source Code

gpio_led_test.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <linux/gpio.h>
#include <sys/ioctl.h>

#define GPIO_CHIP "/dev/gpiochip4"
#define NUM_LEDS  6

int main() {
    int chip_fd;
    struct gpiohandle_request req;
    struct gpiohandle_data data;
    int gpio_lines[NUM_LEDS] = {22, 23, 24, 25, 26, 27};

    chip_fd = open(GPIO_CHIP, O_RDONLY);
    if (chip_fd < 0) {
        fprintf(stderr, "Failed to open %s: %s\n",
                GPIO_CHIP, strerror(errno));
        return 1;
    }

    memset(&req, 0, sizeof(req));
    for (int i = 0; i < NUM_LEDS; i++)
        req.lineoffsets[i] = gpio_lines[i];
    req.lines = NUM_LEDS;
    req.flags = GPIOHANDLE_REQUEST_OUTPUT;
    strcpy(req.consumer_label, "led_test");

    if (ioctl(chip_fd, GPIO_GET_LINEHANDLE_IOCTL, &req) < 0) {
        fprintf(stderr, "Failed to get line handle: %s\n",
                strerror(errno));
        close(chip_fd);
        return 1;
    }

    /* All ON */
    memset(&data, 1, sizeof(data));
    ioctl(req.fd, GPIOHANDLE_SET_LINE_VALUES_IOCTL, &data);
    sleep(2);

    /* One by one ON */
    memset(&data, 0, sizeof(data));
    for (int i = 0; i < NUM_LEDS; i++) {
        data.values[i] = 1;
        ioctl(req.fd, GPIOHANDLE_SET_LINE_VALUES_IOCTL, &data);
        usleep(400000);
    }

    /* Blink 5 times */
    for (int b = 0; b < 5; b++) {
        memset(&data, 1, sizeof(data));
        ioctl(req.fd, GPIOHANDLE_SET_LINE_VALUES_IOCTL, &data);
        usleep(300000);
        memset(&data, 0, sizeof(data));
        ioctl(req.fd, GPIOHANDLE_SET_LINE_VALUES_IOCTL, &data);
        usleep(300000);
    }

    close(req.fd);
    close(chip_fd);
    return 0;
}

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Result

With the LED test harness connected, running the program drives the GPIO lines and lights the LEDs as shown below.