Working with A20 OLinuXino or SOM GPIOs when using new Armbian based A20 universal Linux image

a20

A20 GPIO ports are 32 bit registers listed in alphabetical order PA, PB, PC, PD, PE, PF, PG, PH, PI.

In Armbian GPIO ports are numbered from 0 to 287 corresponding from PA0 to PI31.

The GPIO number is calculating using this formula:

gpioNumber = (Port Letter - 'A') * 32 + pinNumber

 

For instance GREEN STATUS LED on A20-OLinuXino-LIME2 is connected to port PH2. This will correspond to GPIO number:

('H'-'A' = 7) * 32 + 2 = 226

 

All GPIO operations in shell should be made as super user. First we have to register the gpio in the Linux Kernel with this command:

sudo echo 226 > /sys/class/gpio/export

 

to check if we did registered this gpio successfully we use ls command:

sudo ls /sys/class/gpio

 

If you did everything correctly you will see gpio226 listed.

Then you have to specify what will be this GPIO input or output. This is done with writing “in” or “out” in gpioxx direction directory. In this case we want to drive the STATUS LED so we have to make it output:

sudo echo out > /sys/class/gpio/gpio226/direction

 

Once we set the GPIO as output we can write 1 or 0 to it’s value and this will make GPIO port to supply 3.3V when 1 is written or 0V when 0 is written.

To switch the LED on we have to write 1:

sudo echo 1 > /sys/class/gpio/gpio226/value

 

Yay the green LED is now lighting. If we want to switch it off we have to write 0:

sudo echo 0 > /sys/class/gpio/gpio226/value

 

To read the GPIO state it has to be set as input first with the command:

sudo echo in > /sys/class/gpio/gpioXXX/direction

 

where XXX is GPIO port number calculated as described above. Then to read the GPIO state you use this command:

sudo cat /sys/class/gpio/gpioXXX/value

the result will be 0 if the GPIO voltage is between 0.0-1.0V and 1 if the voltage is between 2.3-3.3V. If the voltage on the GPIO is between 1.0 and 2.3V the attempt to read will return randomly value 0 or 1.

Be careful when playing with the GPIO ports, some of them are wired to important peripherials like LCD, Ethernet, USB, SATA etc and writing bad values may break the functionality or even damage the board. Test your knowledge on GPIOs which are not connected to anything is best approach.

We are prepare now new version of PyA20 Python module which will add access to GPIO, SPI, I2C, Serial resources of A20 directly from Python code to work with the new universal A20 Armbian Linux image.

EDIT 2019-01-25 14:24:

We got question how fast is the access to the GPIOs via shell. Sure it’s not fast and made just for slow processes like switching on and off relays, or polling status of buttons or sensors which do not change often their state. Running this code below:

nano toggle_led_lime2.sh

 

Enter inside the file this code:

#!/bin/bash
# the lime2 led is PH2 - 32*(8-1) + 2 = 226

echo 226 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio226/direction
while [ 1 -eq 1 ]
do
echo 1 > /sys/class/gpio/gpio226/value
echo 0 > /sys/class/gpio/gpio226/value
done

 

Save and exit, then make executable and run

chmod +x toggle_led_lime2.sh
./toggle_led_lime2.sh

 

We can see square wave with oscilloscope on PH2 with frequency between 3 and 4 kHz. i.e. pulses with high state 125-150uS and low state 125-150uS.

Shell is slow, if we write same code in C:

#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>

#define PH2        226    // (32 * 7) + 2
#define GPIO_PATH  "/sys/class/gpio/gpio226/value"

int main() {
    int ret;
    int fd;

    fd = open(GPIO_PATH, O_RDWR);
    if (fd < 0)
        return errno;

    while(1) {
        ret = write(fd, "1", 1);
        ret = write(fd, "0", 1);
    }

    return 0;
}

 

The new code produces square wave with 2.13 us high and low state i.e. approx 235 kHz or about 50 times faster than access via shell.

ESP32-EVB our new board for IoT first prototypes are ready

esp32-evbesp32-evb-2

ESP32-EVB is our new board with ESP32-WROOM32 module. It has:

  • ESP32-WROOM32 module
  • two relays 10A/250VAC
  • Ethernet 100Mb interface
  • LiPo charger and step up converter allowing ESP32-EVB to run from LiPo battery
  • microSD card connector
  • two user buttons
  • UEXT connector to attach different sensors and modules
  • 40 pin GPIO 0.1″ step connector with all resources of ESP32
  • 5V power jack
  • three mount holes

Now time to write some examples and if everything works to launch production.

The sale price will be EUR 22.00

Python modules for access to GPIO, I2C and SPI to all OLinuXino boards and SOMs on GitHub

python-logo

We made modules which work same way on all our OLinuXino and SOM boards. The sources are on GitHub.

You can address the GPIOs in two ways – as connector pins and as processor ports.

connector.gpio1p5  means connector GPIO1 pin number 5, same signal can be addressed with port.PG0

Getting started with A13-OLinuXino blog post on element14

Image

 

We spotted blog post on element14 about Getting started with A13-OLinuXino

pyA10Lime 0.1.0. Python library for GPIO access

Image

We just uploaded pyA10Lime https://pypi.python.org/pypi/pyA10Lime/

>>>import A10Lime as lime

# Initialize module
>>>lime.init()

# Read configuration of GPIO
>>>lime.getcfg(lime.PC3)
# or you can use
>>>lime.getcfg(lime.PIN1_29)

# You can address GPIO either by pin numeration or port name
# For example PG0 pin on GPIO-1 connector can be accessed with lime.PG0 or lime.PIN1_5

# Set configuration
>>>lime.setcfg(lime.PC3, lime.OUTPUT)
>>>lime.setcfg(lime.PC3, lime.INPUT)

# Set output level
>>>lime.output(lime.PC3, lime.HIGH)
>>>lime.output(lime.PC3, lime.LOW)

# Read input state
>>>lime.input(lime.PC3)

# Read detailed info about pin
>>>lime.info(lime.PC3)
>>>lime.info(lime.PIN1_29)

New Product in stock: A10-OLinuXino-LIME-UEXT adapter

Image

A10-OLinuXino-LIME-UEXT is adapter board with Male connector on 0.05″ which can connect to A10-OLinuXino-LIME GPIOs with  0.05″ step ribbon CABLE-40-40-10CM and allow LIME GPIOs to be used with BREADBOARD-1, or with A13-LCD43TS, A13-LCD7TS or A13-LCD10TS.

For the moment A20-LCD15.6 is not supported as LVDS signals got noisy when pass through A10-OLinuXino-LIME-UEXT but we are looking for solution.

UEXT signals can be used only when connected to GPIO1. On the other connectors UEXT signals will be not present.

New A20 Android 4.2.2 image now supports all A20-OLinuXino-MICRO hardware features

Image

We received A20-SDK2.0 from Allwinner few weeks ago and were working to generate image for A20-OLinuXino but our aim was to add support to all hardware features the board offers. The process was pretty slow as the compilation is very heavy and even small change requires hours of waiting the image generation to complete.

Now we are ready, the only two features left unsupported are the SATA and second SD-MMC card on the bottom but we think that we should give it a break for a while or our heads will explode 🙂

Two images are uploaded on Wiki: one for 7″LCD and one for 10″LCD, the good news is that the Android 4.2.2 with SDK2.0 now support higher resolution as previous SDK for ICS 4.0.3 had hardcoded 800×600 max resolution which made 10″LCD and HDMI useless.

The image have:

  • LCD and HDMI support at same time
  • Touchscreen support
  • GPIO support – we prepare Android application demo code which show how you can access and use GPIOs under Android
  • I2C1 and I2C2 support – we prepare Android application demo code which show how you can access and use I2C under Android
  • 100Mbit Ethernet
  • USB-Ethernet AX88772
  • USB WiFi RTL8188
  • microSD
  • Audio Out, Audio In
  • USB-OTG device and host with Low/Full/High speed
  • USB HOST upper and bottom with Low/Full/High speed
  • UART6 and UART7 support on UEXT connectors  – we prepare Android application demo code which show how you can access and use UART6,7 under Android
  • Buttons

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