GPIOs

Breakout header

pin	Beta	Mk I
1	Ground	Ground
2	USB 5V	USB 5V
3	GPIO5[27] (CSI0_DAT9)	GPIO5[26] (CSI0_DAT8)
4	UART1_TX / GPIO5[28] (CSI0_DAT10)	GPIO5[27] (CSI0_DAT9)
5	UART1_RX / GPIO5[29] (CSI0_DAT11)	UART1_TX / GPIO5[28] (CSI0_DAT10)
6	GPIO5[30] (CSI0_DAT12)	UART1_RX / GPIO5[29] (CSI0_DAT11)
7	GPIO5[31] (CSI0_DAT13)	GPIO5[30] (CSI0_DAT12)

The breakout header can be accessed, among other options, with a solderless header such as this one or this one (346-87-107-41-036101).

The serial port can be connected to via a USB to TTL cable.

The header can also be used to route I²C (Inter-Integrated Circuit) and SPI (Serial Peripheral Interface) interfaces.

GPIO Sysfs Interface on Linux

When using Linux the 5 GPIOs, exposed on the breakout header (pins 2-7), are easily configurable using the GPIO Sysfs interface.

The following example shows how to set bit 30 of the i.MX53 GPIO5 interface, corresponding to pin 7, in output mode and write 1 and 0 from a Linux shell.

echo 158 > /sys/class/gpio/export             # 128 (GPIO5[0]) + 30 = GPIO5[30]
echo out > /sys/class/gpio/gpio158/direction
echo 1 > /sys/class/gpio/gpio158/value
echo 0 > /sys/class/gpio/gpio158/value

LED Control

The Mk I LED can be controlled in different ways depending on your Linux kernel and Device Tree (dts) configuration. The following examples shows usage on default Debian and Arch Linux images.

Debian examples:

# unload the default LED modules
modprobe -r leds_gpio led_class ledtrig_heartbeat

echo 123 > /sys/class/gpio/export             # 96 (GPIO4[0]) + 27 == GPIO4[27]

# full brightness
echo out > /sys/class/gpio/gpio123/direction
echo 1 > /sys/class/gpio/gpio123/value        # LED off
echo 0 > /sys/class/gpio/gpio123/value        # LED on

# mid-brightness trick
echo in > /sys/class/gpio/gpio123/direction

To permanently disable the default LED usage comment the ledtrig_heartbeat line from /etc/modules and prevent loading of leds_gpio and led_class:

sed -i /etc/modules -e 's/ledtrig_heartbeat/#ledtrig_heartbeat/'
echo -e "blacklist leds_gpio\nblacklist led_class" > /etc/modprobe.d/led-blacklist.conf

Arch Linux examples:

# trigger on USB activity
echo usb-gadget > /sys/devices/platform/leds/leds/LED/trigger

# trigger on microSD activity
echo mmc0 > /sys/devices/platform/leds/leds/LED/trigger

# disable trigger
echo none > /sys/devices/platform/leds/leds/LED/trigger

# LED on
echo 1 > /sys/devices/platform/leds/leds/LED/brightness

# LED off
echo 0 > /sys/devices/platform/leds/leds/LED/brightness