gpio-ts

Linux driver: streaming GPIO timestamps

Project source can be downloaded from https://github.com/alex-konshin/gpio-ts

Author and Contributors

Alex Konshin akonshin@gmail.com

Overview

This project contains source code of Linux driver that currently tested on Raspberry Pi 3, Banana Pi M3, ODROID C2, MinnowBoard Turbot. The main goal of this driver is to simplify developing of applications that need to receive some high frequency signals from GPIO, for example, from RF or IR receivers.
I use this driver for receiving and decoding messages from RF sensors like thermometers. See my another project https://github.com/alex-konshin/f007th-rpi that can use this driver.

What this driver does?

• The driver can serve several GPIO simultaneously. Each GPIO is represented by a separate device file /dev/gpiots*. Each GPIO file may have different filtering settings.
• The driver supports blocking and non-blocking reading and select/poll calls.
• When user application opens device file the driver starts listening of GPIO level changes and creates a stream of 4-byte items. 2 highest bits of an item are the status (0, 1, NOISE or LOST_DATA). Other bits represent the durations of this status in microseconds. Status LOST_DATA means lost interruption due to delays or buffer overflow.
• The driver has built-in filter for received data. It considers too short or too long signals as noise. It also can ignore too short sequences of "good" signals. Basically it allows effectively separate good RF signals from noise for further decoding of them in user application.
• User application actually receives only "good" sequences separated by "noise" items.
• User application can set parameters of the filter by calling ioctl() after opening the device file but before the very first call of select(), poll() or read().
• Application does not need root permissions to open this device file.

Files

How to build

Building on Raspberry Pi

Install Linux headers - see instruction https://www.raspberrypi.org/documentation/linux/kernel/headers.md

Download this driver sources and build it:

cd ~
git clone https://github.com/alex-konshin/gpio-ts.git
cd gpio-ts
make all

The driver file gpio-ts.ko is created in folder ~/gpio-ts.

Building on ODROID C2

Download and setup Linux headers:

git clone --depth 1 https://github.com/hardkernel/linux.git -b odroidc2-3.14.y
cd /lib/modules/$(uname -r)
sudo ln -s /usr/src/linux-headers-$(uname -r) build

Download this driver sources and build it:

cd ~
git clone https://github.com/alex-konshin/gpio-ts.git
cd gpio-ts
make all

The driver file gpio-ts.ko is created in folder ~/gpio-ts.

Building on MinnowBoard

Install Linux headers:

sudo apt-get install linux-headers-$(uname -r)

Install make, gcc and g++ if they are not installed yet:

sudo apt install make
sudo apt install gcc
sudo apt install g++

Download this driver sources and build it:

cd ~
git clone https://github.com/alex-konshin/gpio-ts.git
cd gpio-ts
make all

The driver file gpio-ts.ko is created in folder ~/gpio-ts.

Building on Banana Pi M3

Building Linux kernel module on BPI-M3 is currently a nightmare. I finally figured out how to cross-compile it on another machine and after some hacks I was able to load and use it. But I don't remember all steps I did to achieve it. To make your life easier I provided compiled driver for the current BPI-M3 kernel. Take it from folder bpi-m3-kernel-3.4.39.

Loading and unloading the driver.

Important note for Banana Pi M3

Not all GPIOs allow to set interruptions handler. This is a hardware limitation. The following GPIO numbers are supported on BPI-M3:
32, 33, 34, 35, 202, 203, 204, 205, 226, 227, 228, 229, 234, 360, 361, 362.
See output of command gpio readall to find these GPIOs on the connector.

Module parameters:

gpios

The comma-separated list of GPIOs that will be served by this driver. Device /dev/gpiots* will be created for each GPIO from this list.

min_duration

Minimum duration of the same level to be accepted. This is an optional parameter. It sets the default value that can be changed for a particular GPIO by user application.

max_duration

Maximum duration of the same level to be accepted. This is an optional parameter. It sets the default value that can be changed for a particular GPIO by user application.

min_seq_len

Minimum sequence length to be accepted. This is an optional parameter. It sets the default value that can be changed for a particular GPIO by user application.

Examples:

sudo insmod gpio-ts.ko gpios=27
sudo insmod gpio-ts.ko gpios=21,27 min_duration=400 max_duration=1100 min_seq_len=100

Unloading the driver

sudo rmmod gpio-ts