Running RTEMS on Raspberry Pi 4B

Shaunak Datar
#RTEMS  #Raspberry Pi  #Bare-metal  #GSoC 

RTEMS (Real-Time Executive for Multiprocessor Systems) is a real-time operating system used in embedded systems, offering a rich set of Board Support Packages (BSPs) for various platforms. One such platform is the Raspberry Pi 4B, a popular board among hobbyists, educators, and industry professionals. In this post, I’ll walk you through setting up RTEMS on the Raspberry Pi 4B from scratch.

Let’s dive in!

🚀 Setting Up the Environment

First, create a working directory. Ensure that git is installed on your host machine.

mkdir -p $HOME/quick-start/src
cd $HOME/quick-start/src

Clone the necessary repositories:

git clone https://gitlab.rtems.org/rtems/tools/rtems-source-builder.git rsb
git clone https://gitlab.rtems.org/rtems/rtos/rtems.git

The rtems repo contains the RTEMS source, while rsb (RTEMS Source Builder) helps you build the toolchain and BSP.

🔧 Installing the Toolchain

Now, build and install the AArch64 toolchain for the Raspberry Pi 4B:

cd $HOME/quick-start/src/rsb/rtems
../source-builder/sb-set-builder --prefix=$HOME/quick-start/rtems/7 7/rtems-aarch64

Once completed, verify the toolchain:

$HOME/quick-start/rtems/7/bin/aarch64-rtems7-gcc --version

🧱 Building the BSP

Let’s build the aarch64/raspberrypi4b BSP.

cd $HOME/quick-start/src/rtems
echo "[aarch64/raspberrypi4b]" > config.ini
./waf configure --prefix=$HOME/quick-start/rtems/7
./waf
./waf install

📝 Creating the RTEMS Application

Now that the BSP is ready, let’s write a basic RTEMS application.

mkdir -p $HOME/quick-start/src/app/hello
cd $HOME/quick-start/src/app/hello

Download Waf and make it executable:

curl https://waf.io/waf-2.0.19 > waf
chmod +x waf

Initialize a Git repo and add RTEMS Waf support:

git init
git submodule add https://gitlab.rtems.org/rtems/tools/rtems_waf.git rtems_waf

🛠 wscript

from __future__ import print_function

rtems_version = "7"

try:
    import rtems_waf.rtems as rtems
except:
    print('error: no rtems_waf git submodule')
    import sys
    sys.exit(1)

def init(ctx):
    rtems.init(ctx, version = rtems_version, long_commands = True)

def bsp_configure(conf, arch_bsp):
    pass

def options(opt):
    rtems.options(opt)

def configure(conf):
    rtems.configure(conf, bsp_configure = bsp_configure)

def build(bld):
    rtems.build(bld)

    bld(features = 'c cprogram',
        target = 'hello.exe',
        cflags = '-g -O2',
        source = 'hello.c')

💬 hello.c

#include <rtems.h>
#include <stdlib.h>
#include <stdio.h>

rtems_task Init(rtems_task_argument ignored)
{
  printf("\nHello World\n");
  printf("I am Shaunak Datar\n");
  exit(0);
}

#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
#define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
#define CONFIGURE_UNLIMITED_OBJECTS
#define CONFIGURE_UNIFIED_WORK_AREAS
#define CONFIGURE_RTEMS_INIT_TASKS_TABLE
#define CONFIGURE_INIT

#include <rtems/confdefs.h>

Configure and build the app:

./waf configure --rtems=$HOME/quick-start/rtems/7 --rtems-bsp=aarch64/raspberrypi
./waf

Create the bootable kernel image:

~/quick-start/rtems/7/bin/aarch64-rtems7-objcopy -Obinary build/aarch64-rtems7-raspberrypi4b/hello.exe build/kernel8.img

Copy kernel8.img to your SD card. In the SD card’s config.txt, add:

arm_64bit=1
dtoverlay=disable-bt

📟 Connecting to the Raspberry Pi

Wiring (via USB-to-UART):

  • Pi Pin 8 (TX) → USB RX
  • Pi Pin 10 (RX) → USB TX
  • Pi GND → USB GND

Find your USB device:

ls /dev/cu.*

Use minicom or any serial terminal at 115200 baud, 8N1 settings.

You should see something like this: RTEMS Hello World on Raspberry Pi

That’s it! You’ve now got RTEMS running on your Raspberry Pi 4B.

Want to know more about my work on this? Check out my GSoC 2025 RTEMS project.

Happy hacking! 🤓