Controlling GPIOs and LEDs

This example demonstrates how to use GPIOs with ZentriOS in general, and how to use GPIOs to control LEDs on Zentri evaluation boards. For details of using GPIOs and peripherals, see Peripherals.

In ZentriOS, a GPIO may have two functions: a standard IO function or an alternative function such as a system indicator, status GPIO or control GPIO. See GPIO Configuration.

When a GPIO is configured with an alternative function, the standard IO function is NOT available and the gpio_dir, gpio_set, and gpio_get commands are disabled for that GPIO.

Before a GPIO can be used to control an LED, it is necessary to first check whether the GPIO is being used for an alternative function. If a GPIO is not being used for an alternative function, but is already in use as a standard GPIO (for another purpose), the GPIO must first be freed up by setting the direction of the GPIO to none using the gpio_dir command.

GPIO Usage

The gpio.usage variable makes it easy to get a list of GPIOs that are already in use. The session in the following table shows the GPIO usage after factory reset for a Mackerel Evaluation Board (schematics: AMW004-E03 Rev 1).

ZentriOS Session (AMW004-E03 Rev 1)

> get gpio.usage
! #   Description
#10 - Standard I/O
#11 - Standard I/O
#13 - UART1 RX
#14 - UART1 TX
#17 - SPI CLK
#18 - SPI MOSI
#19 - SPI MISO
#21 -
#22 - system.indicator.wlan

LED Control

The following example is based on the first revision of a Mackerel evaluation board which only has two LEDs connected to GPIO 21 & 22. These LEDs are factory configured as system indicators to dynamically indicate the state of the Wi-Fi and network connection (as shown in the table above). To repurpose the GPIOs as standard IOs for use with LEDs, try the ZentriOS command sequence shown in the table below.

Note! Don't forget to adjust the GPIO numbers to suit your specific board!

ZentriOS Commands (for AMW004-E03 Rev1) Command Description

set system.indicator.gpio wlan    -1
set system.indicator.gpio network -1

set gpio.alias 21 LED1
set gpio.alias 22 LED2

gpio_dir LED1 out
gpio_dir LED2 out

gpio_set LED1 1
gpio_set LED2 1

gpio_set LED1 0
gpio_set LED2 0

<- Disable the wlan system indicator
<- Disable the network system indicator
<- Save & reboot since system indicator
   functions are setup after a reset

<- Setup a friendly alias for the LED on GPIO 21
<- Setup a friendly alias for the LED on GPIO 22

<- Set the GPIO direction to output
<- Set the GPIO direction to output

<- Turn on LED 1
<- Turn on LED 2

<- Turn off LED 1
<- Turn off LED 2

To re-instate the system indicators, either factory reset the module, or use the following commands.

ZentriOS Commands Command Description

gpio_dir LED1 none
gpio_dir LED2 none

set system.indicator.gpio wlan    LED1
set system.indicator.gpio network LED2

<- Free up the GPIO aliased to LED1
<- Free up the GPIO aliased to LED2

<- Set the wlan system indicator GPIO to LED1
<- Set the wlan system indicator GPIO to LED2
<- Save & reboot since system indicator
   functions are setup after a reset

GPIO Initialization

To simplify GPIO setup (on boot up), ZentriOS provides the option to automatically configure GPIOs with a GPIO configuration script set using the gpio.config_file variable. Alternatively, GPIOs may be individually configured for initialization after reset using the gpio.init variable. Don't forget to save & reboot to make sure recent GPIO initialization changes take effect.

Supporting ZentriOS Editions and Versions

Change Log