General Purpose Input/Output (GPIO)

The NXP i.MX6UL 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 6UL platforms

On the ConnectCore 6UL system-on-module:
- Many of the i.MX6UL GPIOs are available at the system-on-module, multiplexed with other functions (labeled GPIOxIOy where _x is the port and y is the GPIO pin). See Hardware reference manuals for information about GPIO pins and their multiplexed functionality.
- Eight MCA GPIO pins are available (labeled MCA_IOx where x is the GPIO pin).
On the ConnectCore 6UL SBC Express, the expansion connector allows direct access to several i.MX6UL GPIOs and MCA GPIOs.
On the ConnectCore 6UL SBC Pro board, an I/O Expander chip features up to 39 GPIO pins (multiplexed with Analog-to-Digital Converter (ADC) functionality). See I/O Expander GPIO for additional information on I/O Expander GPIOs. The GPIO connector allows direct access to several i.MX6UL GPIOs, MCA GPIOs, and I/O Expander 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

You can manage the user space interface with GPIOs through the kernel configuration option:

/sys/class/gpio/… (sysfs interface) (CONFIG_GPIO_SYSFS)

This option is enabled as built-in on the default ConnectCore 6UL kernel configuration file.

Support for i.MX6UL GPIOs is automatically provided through the non-visible option CONFIG_GPIO_MXC.

Kernel driver

The driver for the i.MX6UL GPIO is located at:

File	Description
drivers/gpio/gpio-mxc.c	i.MX6UL GPIO driver

File

Description

drivers/gpio/gpio-mxc.c

i.MX6UL GPIO driver

Device tree bindings and customization

The i.MX6UL GPIO device tree binding is documented at Documentation/devicetree/bindings/gpio/fsl-imx-gpio.txt.

One GPIO controller is defined for each i.MX6UL GPIO port in the common i.MX6UL device tree file:

i.MX6UL device tree

gpio1: gpio@0209c000 {
	compatible = "fsl,imx6ul-gpio", "fsl,imx35-gpio";
	reg = <0x0209c000 0x4000>;
	interrupts = <GIC_SPI 66 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 67 IRQ_TYPE_LEVEL_HIGH>;
	gpio-controller;
	#gpio-cells = <2>;
	interrupt-controller;
	#interrupt-cells = <2>;
	gpio-ranges = <&iomuxc  0 23 10>, <&iomuxc 10 17 6>,
			<&iomuxc 16 33 16>;
};

[...]

gpio5: gpio@020ac000 {
	compatible = "fsl,imx6ul-gpio", "fsl,imx35-gpio";
	reg = <0x020ac000 0x4000>;
	interrupts = <GIC_SPI 74 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 75 IRQ_TYPE_LEVEL_HIGH>;
	gpio-controller;
	#gpio-cells = <2>;
	interrupt-controller;
	#interrupt-cells = <2>;
	gpio-ranges = <&iomuxc 0 7 10>, <&iomuxc 10 5 2>;
};

The ConnectCore 6UL device tree include file and the carrier board device tree files use the i.MX6UL GPIOs.

For example, on the ConnectCore 6UL, GPIO5_IO04 is used as interrupt line from the MCA, and GPIO4_IO14 is used to activate internal circuitry during the MCA firmware update:

ConnectCore 6UL device tree

mca_cc6ul: mca@7e {
	compatible = "digi,mca-cc6ul";
	reg = <0x7e>;
	interrupt-parent = <&gpio5>;
	interrupts = <4 IRQ_TYPE_EDGE_FALLING>;
	interrupt-controller;
	#interrupt-cells = <2>;
	fw-update-gpio = <&gpio4 14 GPIO_ACTIVE_LOW>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_mca_cc6ul>;

[...]
};

For example, on the ConnectCore 6UL SBC Pro, GPIO5_IO06 is used to reset the PHY of ENET2 Ethernet interface:

ConnectCore 6UL SBC Pro device tree

&fec2 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_enet2>,
		    <&pinctrl_enet2_mdio>,
		    <&pinctrl_enet2_gpio>;
	phy-mode = "rmii";
	phy-handle = <&ethphy1>;
	phy-reset-gpios = <&gpio5 6 GPIO_ACTIVE_LOW>;
	phy-reset-duration = <26>;
	digi,phy-reset-in-suspend;

	[...]
};

IOMUX configuration

You must configure the pads that are to be used as i.MX6UL 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 6UL example from above, mca_cc6ul node configures pinctrl_mca_cc6ul:

ConnectCore 6UL device tree

pinctrl_mca_cc6ul: mcagrp {
	fsl,pins = <
		/* MCA_nINT */
		MX6UL_PAD_SNVS_TAMPER4__GPIO5_IO04	0xb0b1
		/* MCA_FW_UPDATE */
		MX6UL_PAD_NAND_CE1_B__GPIO4_IO14	0x30
	>;
};

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 6UL SBC Express expansion connector:

Pad	Signal	GPIO
11	GPIO3_4	GPIO3_IO04
12	JTAG_TDI/GPIO1_13	GPIO1_IO13
13	GPIO3_10_PROT	GPIO3_IO10
15	JTAG_MOD/GPIO1_10	GPIO1_IO10
16	JTAG_TMS/GPIO1_11	GPIO1_IO11
18	GPIO3_12_PROT	GPIO3_IO12
27	PWM2/I2C3_SCL_PROT	GPIO3_IO06
29	GPIO5	GPIO1_IO05
32	PWM4_PROT	GPIO3_IO08
33	GPIO3_7/PWM3_PROT	GPIO3_IO07
35	JTAG_TDO/GPIO1_12	GPIO1_IO12
36	CSI_MCLK	GPIO4_IO17
37	CSI_PIXCLK	GPIO4_IO18
38	JTAG_nTRST/GPIO1_15	GPIO1_IO15
40	JTAG_TCK/GPIO1_14	GPIO1_IO14

Pad

Signal

GPIO

GPIO3_4

GPIO3_IO04

JTAG_TDI/GPIO1_13

GPIO1_IO13

GPIO3_10_PROT

GPIO3_IO10

JTAG_MOD/GPIO1_10

GPIO1_IO10

JTAG_TMS/GPIO1_11

GPIO1_IO11

GPIO3_12_PROT

GPIO3_IO12

PWM2/I2C3_SCL_PROT

GPIO3_IO06

GPIO5

GPIO1_IO05

PWM4_PROT

GPIO3_IO08

GPIO3_7/PWM3_PROT

GPIO3_IO07

JTAG_TDO/GPIO1_12

GPIO1_IO12

CSI_MCLK

GPIO4_IO17

CSI_PIXCLK

GPIO4_IO18

JTAG_nTRST/GPIO1_15

GPIO1_IO15

JTAG_TCK/GPIO1_14

GPIO1_IO14

On the ConnectCore 6UL SBC Pro GPIO connector:

Pad Signal GPIO

12

EXP_GPIO_2

GPIO1_IO03

Pad	Signal	GPIO
12	EXP_GPIO_2	GPIO1_IO03

SION bit

It is not possible to read the real signal level of a GPIO pin that is configured as an output. You can use the software input on (SION) bit to read the value of an output GPIO.

SION bit mode increases the power consumption of the module, so it is disabled by default.

To enable the SION bit, set the bit 30 (special value). In other words, do an OR mask of your previous value with 0x40000000:

ConnectCore 6UL SBC Express device tree

&iomuxc {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_hog>;

	pinctrl_hog: hoggrp {
		fsl,pins = <
			/* GPIO3_IO04 on Expansion connector (SION enabled)*/
			MX6UL_PAD_LCD_RESET__GPIO3_IO04         0x4000f030
		>;
	};

	[...]
};

For more information, see the NXP Application Note AN5078.

Using the GPIOs

You can access the GPIOs from the sysfs. See the Linux kernel documentation at Documentation/gpio/sysfs.txt.

Calculate the Linux GPIO number of a GPIO pin

For each GPIO controller entry on the device tree, Linux creates an entry /sys/class/gpio/gpiochipN, where N is an integer number starting at 0, with the following read-only attributes:

base: same as N, the first GPIO managed by this chip
label: provided for diagnostics (not always unique)
ngpio: the number of GPIOs this controller manages (from N to N + ngpio - 1)

GPIOs on the ConnectCore 6UL system-on-module

Every GPIO port of the i.MX6UL CPU is a different GPIO controller and thus has its own /sys/class/gpio/gpiochipN entry on the sysfs.

On the default ConnectCore 6UL system-on-module device tree, the i.MX6UL CPU’s GPIO ports are probed first:

PORT1: /sys/class/gpio/gpiochip0
PORT2: /sys/class/gpio/gpiochip32
PORT3: /sys/class/gpio/gpiochip64
PORT4: /sys/class/gpio/gpiochip96
PORT5: /sys/class/gpio/gpiochip128

Calculate the Linux GPIO number for a certain GPIO pin by adding the GPIO pin index to the port base index. For instance:

i.MX6UL GPIO2_IO4 (port 2, pin 4) is: 32 + 4 = 36

Since the i.MX6UL CPU has five ports, all of which have 32 pins, the following formula also applies to i.MX6UL CPU GPIOs (without requiring the user to know the GPIO base of each port):

\$"LinuxGPIO_num" = ("<imx6ul_gpio_port>" - 1) * 32 + "<imx6ul_gpio_pin>"\$

For example, i.MX6UL GPIO2_IO4 (port 2, pin 4) translates to:

\$(color(red)(2) - 1) * 32 + color(red)(4) = 36\$

Example: write from sysfs

The ConnectCore 6UL SBC Express has GPIO3_IO04 on the expansion connector. To drive this as an ouput:

Calculate the Linux GPIO number:

\$"GPIO3_IO04" -> (color(red)(3) - 1) * 32 + color(red)(4) = 68\$
Request the GPIO:
```
~# echo 68 > /sys/class/gpio/export
```

Configure the GPIO as output:

~# echo out > /sys/class/gpio/gpio68/direction

Drive the GPIO high:

~# echo 1 > /sys/class/gpio/gpio68/value

Drive the GPIO low:

~# echo 0 > /sys/class/gpio/gpio68/value

When you are done using the GPIO, free it with:
```
~# echo 68 > /sys/class/gpio/unexport
```

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 6UL 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.

See I/O Expander for additional information on I/O Expander GPIOs.