The NXP i.MX8M Mini CPU has five GPIO ports. Each port can generate and control 32 signals.

The MCA also features a number of GPIO pins (multiplexed with Analog-to-Digital Converter (ADC) functionality). See MCA I/O pads for a list of all available MCA IOs and their capabilities.

GPIOs on the ConnectCore 8M Mini platforms

  • On the ConnectCore 8M Mini system-on-module:

    • Many of the i.MX8M Mini GPIOs are available at the system-on-module, multiplexed with other functions (labeled GPIOx_IOy where x is the port and y is the GPIO pin). See Hardware reference manuals for information about GPIO pins and their multiplexed functionality.

    • 15 MCA GPIO pins are available (labeled MCA_IOx where x is the GPIO pin).

  • On the ConnectCore 8M Mini Development Kit, the expansion connectors allow direct access to some of the i.MX8M Mini GPIOs.

GPIOs on the SOM and carrier board are used for many purposes, such as:

  • Power enable line for transceivers

  • Reset line for controllers

  • LCD backlight control

  • Interrupt line

  • User LED

  • User button

Kernel configuration

Support for i.MX8M Mini GPIOs is automatically provided through the non-visible option CONFIG_GPIO_MXC.

Kernel driver

The driver for the i.MX8M Mini GPIO is located at:

File Description

drivers/gpio/gpio-mxc.c

i.MX8M Mini GPIO driver

Device tree bindings and customization

The i.MX8M Mini GPIO device tree binding is documented at Documentation/devicetree/bindings/gpio/fsl-imx-gpio.txt.

One GPIO controller is defined for each i.MX8M Mini GPIO port in the common i.MX8M Mini device tree file:

i.MX8M Mini device tree
	gpio1: gpio@30200000 {
		compatible = "fsl,imx8mm-gpio", "fsl,imx35-gpio";
		reg = <0x0 0x30200000 0x0 0x10000>;
		interrupts = <GIC_SPI 64 IRQ_TYPE_LEVEL_HIGH>,
			     <GIC_SPI 65 IRQ_TYPE_LEVEL_HIGH>;
		gpio-controller;
		#gpio-cells = <2>;
		interrupt-controller;
		#interrupt-cells = <2>;
	};
 
[...]
 
	gpio5: gpio@30240000 {
		compatible = "fsl,imx8mm-gpio", "fsl,imx35-gpio";
		reg = <0x0 0x30240000 0x0 0x10000>;
		interrupts = <GIC_SPI 72 IRQ_TYPE_LEVEL_HIGH>,
			     <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>;
		gpio-controller;
		#gpio-cells = <2>;
		interrupt-controller;
		#interrupt-cells = <2>;
	};

The ConnectCore 8M Mini device tree include file and the carrier board device tree files use the i.MX8M Mini GPIOs.

For example, on the ConnectCore 8M Mini, GPIO3_IO08 is used as the MCA interrupt line, and GPIO1_IO4 is used to activate internal circuitry during the MCA firmware update:

ConnectCore 8M Mini device tree
	mca_cc8m: mca@63 {
		compatible = "digi,mca-cc8m";
		reg = <0x63>;
		interrupt-parent = <&gpio2>;
		interrupts = <10 IRQ_TYPE_LEVEL_HIGH>;
		interrupt-controller;
		#interrupt-cells = <2>;
		fw-update-gpio = <&gpio1 5 GPIO_ACTIVE_LOW>;
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_mca_cc8m>;
 
		[...]
};

For example, on the ConnectCore 8M Mini Development Kit, GPIO5_IO3 is used to reset the PHY of ENET1 Ethernet interface:

ConnectCore 8M Mini Development Kit device tree
&fec1 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_fec1_gpio>,
		    <&pinctrl_fec1>;
	phy-mode = "rgmii-id";
	phy-handle = <&ethphy0>;
	digi,mdio-lt-supply = <&reg_1v8_ext>;
	phy-supply = <&reg_3v3_eth0>;
	phy-reset-gpios = <&gpio5 3 GPIO_ACTIVE_LOW>;
	phy-reset-duration = <1>;
	digi,phy-reset-in-suspend;
	fsl,magic-packet;
	status = "okay";

	[...]
};

IOMUX configuration

You must configure the pads that are to be used as i.MX8M Mini GPIOs. See Pin multiplexing (IOMUX).

For GPIOs that are managed by other drivers, you must configure their pad IOMUX inside the driver node specific pinctrl-0 to work according to the specified interface functionalities.

On the ConnectCore 8M Mini example from above, mca_cc8m node configures pinctrl_mca_cc8m:

ConnectCore 8M Mini device tree
pinctrl_mca_cc8m: mcagrp {
	fsl,pins = <
		/* MCA_nINT */
		MX8MM_IOMUXC_SD1_RESET_B_GPIO2_IO10	0x56
		/* MCA_FW_UPDATE */
		MX8MM_IOMUXC_GPIO1_IO05_GPIO1_IO5	0x16
	>;
};

For GPIOs that are not associated with any interface or that can’t be handled by a driver, see Configure independent pin IOMUX and pad control. The following external pads are configured as GPIOs on the default device tree:

  • On the ConnectCore 8M Mini Development Kit J46 expansion connector:

    Pad Signal GPIO

    3

    GPIO1_IO10

    GPIO1_IO10

    4

    GPIO1_IO15

    GPIO1_IO15

    5

    GPIO1_IO11

    GPIO1_IO11

    7

    GPIO1_IO13

    GPIO1_IO13

    9

    GPIO1_IO14

    GPIO1_IO14

  • On the ConnectCore 8M Mini Development Kit J48 expansion connector:

    Pad Signal GPIO

    5

    EXP_I2C_IRQ_N

    GPIO5_IO27

    7

    EXP_I2C_GPIO

    GPIO5_IO26

  • User LED 3 is GPIO2_IO19

  • User button 2 is GPIO2_IO20

GPIO pads power domains

The i.MX8M Mini GPIOs are configurable and can work at 1.8V or 3.3V depending on the power domain of the pad they are on.

To determine the working voltage of a given GPIO:

  1. Locate the pad of a given signal on the ConnectCore 8M Mini Development Kit schematics. For instance, on the ConnectCore 8M Mini Development Kit, signal UART4_TX comes from pad UART4_TXD of the ConnectCore 8M Mini SOM:

    dwg gpiopad sch 8m

  2. Locate this pad on the IMOUX section of the ConnectCore 8M Mini Hardware Reference Manual. This table lists the associated GPIO of the pad, and the power domain it is on:

    dwg gpiopad hrm som 8m

  3. Locate the power domain (VDD_UART on the example) on the ConnectCore 8M Mini Development Kit schematics. Here you can tell the voltage of the power domain:

    dwg power domain sch 8m

Using the GPIOs

The package libgpiod (added by packagegroup-dey-core) provides a set of tools (gpioset, gpioget…​) for controlling the GPIOs from user space.

You can still control the GPIOs from the sysfs, but this ABI is not recommended. See https://www.kernel.org/doc/html/latest/admin-guide/gpio/sysfs.html.

Detect GPIO ports

Use gpiodetect to list the GPIO ports detected by the kernel:

~# gpiodetect
gpiochip0 [gpio1] (32 lines)
gpiochip1 [gpio2] (32 lines)
gpiochip2 [gpio3] (32 lines)
gpiochip3 [gpio4] (32 lines)
gpiochip4 [gpio5] (32 lines)
gpiochip5 [mca-gpio] (19 lines)
gpiochip6 [spi2.0] (2 lines)

where:

  • Ports gpio1 to gpio5 are the i.MX8M Mini GPIO ports.

  • Port mca-gpio is the MCA GPIO port.

  • Port spi2.0 is the external CAN controller on the ConnectCore 8M Mini Development Kit.

Information about a GPIO port

Use gpioinfo to list the lines of a given port:

~# gpioinfo gpio1
gpiochip0 - 32 lines:
	line   0:      unnamed       unused   input  active-high
	line   1:      unnamed       unused   input  active-high
	line   2:      unnamed       unused   input  active-high
	line   3:      unnamed        "rts"  output  active-high [used]
	line   4:      unnamed       unused   input  active-high
	line   5:      unnamed "mca-fw-update" output active-high [used]
	line   6:      unnamed "regulators:regulator@4" output active-high [used]
	line   7:      unnamed       unused  output  active-high
	line   8:      unnamed       unused  output  active-high
	line   9:      unnamed       unused   input  active-high
	line  10:      unnamed       unused   input  active-high
	line  11:      unnamed       unused   input  active-high
	line  12:      unnamed       unused  output  active-high
	line  13:      unnamed       unused   input  active-high
	line  14:      unnamed       unused   input  active-high
	line  15:      unnamed       unused   input  active-high
	line  16:      unnamed       unused   input  active-high
	line  17:      unnamed       unused   input  active-high
	line  18:      unnamed       unused   input  active-high
	line  19:      unnamed       unused   input  active-high
	line  20:      unnamed       unused   input  active-high
	line  21:      unnamed       unused   input  active-high
	line  22:      unnamed       unused   input  active-high
	line  23:      unnamed       unused   input  active-high
	line  24:      unnamed       unused   input  active-high
	line  25:      unnamed       unused   input  active-high
	line  26:      unnamed       unused   input  active-high
	line  27:      unnamed       unused   input  active-high
	line  28:      unnamed       unused   input  active-high
	line  29:      unnamed       unused   input  active-high
	line  30:      unnamed       unused   input  active-high
	line  31:      unnamed       unused   input  active-high

Set an output high/low

Use gpioset to set a i.MX8M Mini GPIO as output, such as GPIO5_IO27. Use =1 to set it high, or =0 to set it low:

~# gpioset gpio5 27=1
~# gpioset gpio5 27=0

Read an input

Use gpioget to read the value of a i.MX8M Mini GPIO input, such as GPIO5_IO27:

~# gpioget gpio5 27
0

Use a GPIO as interrupt

Use gpiomon to wait for an event on a given GPIO, such as GPIO5_IO27:

~# gpiomon --num-events 1 --rising-edge gpio5 27

See the README of libgpiod for more information on the usage of these tools.

Sample application

An example application called apix-gpio-example is included in the dey-examples-digiapix recipe (part of dey-examples package) of meta-digi layer. This application shows how to manage GPIO lines using the Digi APIx library on the ConnectCore 8M Mini platform.

Go to GitHub to see the application instructions and source code.

See GPIO API for more information about the GPIO APIx.

See MCA General Purpose Input/Output (GPIO) for additional information on MCA GPIOs.