IRBlaster

IRBlaster is a Linux kernel driver for transmitting IR signals on Raspberry Pi using hardware PWM.

Features

• Hardware PWM for maximum accuracy and low CPU overhead
• Implemented as Linux kernel driver
• All the heavy lifting done within the driver (High-precision, time-constrained operations)
• Holds the scheduler with spinlock and disables interrupts for duration of the transmission
• Bypasses GPIO root requirements by creating character device: /dev/irblaster
• Comes with header-only usermode library for simple access as well as usage examples (Go & C)
• Supports all Raspberry Pi devices from zero to 4 (Only tested with 3B+)

Limitations

• Currently only GPIO 18 supported.

Portability

• Should work with any "modern" Raspbian installation
• Should also work on other distributions (not tested)

Installation

First make sure you are up-to-date:

$ apt-get update -y
$ apt-get upgrade -y

Kernel headers

In order to build linux kernel modules, you'll have to have matching kernel headers to the kernel you are running.

If you are on Raspbian, you can just run:

$ sudo apt-get install raspberrypi-kernel-headers

On Debian-based platforms:

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

On other distributions, you'll have to figure this out yourself.

You can check that the header are successfully installed by running:

$ ls /lib/modules/$(uname -r)/build

If the build folder is not found or is empty, headers have not been properly installed for your kernel version.

Non-root access (optional)

The driver will create a character device at /dev/irblaster, which by default requires root privileges.

You can make it accessible to non-root users without sudo by creating udev rule file:

$ sudo touch /etc/udev/rules.d/99-irblaster.rules

and writing inside the file:

KERNEL=="irblaster", SUBSYSTEM=="ir", MODE="0666"

Build the driver

Build the driver (and example):

$ make         # build the driver for rpi 2/3 (most common target) and usage examples (Go & C)
$ make rpi#    # replace the # with anything from 0-4 depending on your Raspberry Pi model.
$ make example # build only the usage examples (Go & C)

Load the driver to Kernel

$ sudo insmod kernel/irblaster.ko

You can check from /var/log/kern.log whether the driver was successfully loaded.

Usage

Make sure your IR led or controlling transistor is plugged into (BCM#) GPIO 18.

You can send IR transmissions by writing to the device.

NEC-protocol implementation in the example/test.c:

#include "../user/ib.h"
 
int main() {
   char *buffer;
   unsigned lpw = 9000;  // leading pulse width
   unsigned lgw = 4500;  // leading gap width
   unsigned opw = 560;   // one pulse width
   unsigned ogw = 1680;  // one gap width 
   unsigned zpw = 560;   // zero pulse width
   unsigned zgw = 560;   // zero gap width
   unsigned utp = 560;   // trailing pulse width
   unsigned f = 38000;   // frequency in hz (NEC: 38 kHz)
   unsigned dc_n = 50;   // Pulse within duty cycle period
   unsigned dc_m = 100;  // Duty cycle period
   char *binary = "11001101001100100000111111110000"; // actual payload to be transmitted

   sendIR(lpw, lgw, opw, ogw, zpw, zgw, utp, f, dc_n, dc_m, binary);
   return 0;
}

For detailed example of writing to the device see user/ib.h user mode library.

All the variables are 32-bit unsigned integers except the data string which can be up to 200 bytes.

Contributing

• Pull requests are welcome.
• For major changes, please open an issue first to discuss what you would like to change.
• Project uses Google C style. You can use the clang-format bash script to automatically format all the .h and .c files in the project.

Roadmap

Near future

• Support for different GPIOs and PWM channels

Some day

• Direct Memory Access (DMA) support to transmit on any GPIO

References

• BCM2835 ARM Peripherals
• Linux Device Drivers, Third Edition

License

MIT