RTOS (REAL TIME OPERATING SYSTEM)

When it Matters, it Runs on RTOS

Realtime computing Myth V/S Truth

Myth : RTC (Real Time computing) is fast computing with higher performance

Truth : RTC is predictable computing , timeliness is more important than perfomance.

• RTOS deals with gurantees , not with raw speed . having more processor , more RAM ,faster BUS interfaces does't make a system real time , it deals with GUARANTEES

What RTOS needs to be Deterministic

• Interrupt & Context switch

• Preemption

• Latency

• Jitter

• Faster

• Linux mainline kernel was not designed as RTOS

Distributions

• FreeRTOS : FreeRTOS is a class of RTOS that is designed to be small enough to run on a microcontroller - although its use is not limited to microcontroller applications.

• QNX : QNX is real time RTOS, which support ARM, MIPS, PowerPC, SH and X86 Processor family.

• Vxworks :Vxworks is also real time rtos, it support wide range of processor architectures like ARM, PowerPC, ColdFire, MIPS etc.

• RTlinux :RTLinux is a hard realtime real-time operating system (RTOS) microkernel that runs the entire Linux operating system as a fully preemptive process. The hard real-time property makes it possible to control robots, data acquisition systems, manufacturing plants, and other time-sensitive instruments and machines from RTLinux applications. Even with a similar name it is not related the Real-Time Linux project of the Linux Foundation.

• ChibiOS/RT: is designed for embedded applications on 8, 16 and 32 bit microcontrollers; size and execution efficiency are the main project goals.[2] As reference, the kernel size can range from a minimum of 1.2 Kib up to a maximum of 5.5 KiB with all the subsystems activated on a STM32 Cortex-M3 processor. The kernel is capable of over 220,000 created/terminated threads per second and is able to perform a context switch in 1.2 microseconds on an STM32 @ 72 MHz. Similar metrics for all the supported platforms are included in the source distribution as test reports.

  • Efficient and portable preemptive kernel.
  • Best in class context switch performance.
  • Many supported architectures and platforms.
  • Static architecture, everything is statically allocated at compile time.
  • Dynamic extensions, dynamic objects are supported by an optional layer built on top of the static core.
  • Rich set of primitives: threads, virtual timers, semaphores, mutexes, condition variables, messages, mailboxes, event flags, queues.
  • Support for priority inheritance algorithm on mutexes.
  • Hardware Abstraction Layer (HAL) component supporting a variety of abstract device drivers: Port, Serial, ADC, CAN, EXT, GPT, I2C, ICU, MAC, MMC, PWM, RTC, SDC, SPI, UART, USB, USB-CDC.
  • Support for external components uIP, lwIP, FatFs.
  • Extensive test suite with benchmarks.
  • Support for C++ applications.

github :https://github.com/ChibiOS/

projects

1. Arduino UNO (ATmega328P 8-bit μc) OS: FreeRTOS lib:https://github.com/feilipu/Arduino_FreeRTOS_Library

   • Example 1 [blink AnalogRead]
   • Example 2 [ultrasonic sensor response at Real time]

2. Raspberry Pi 3 Model B+

   OS :RTlinux

   cross compile the RTlinux on any linux distro

   Step 1. Download the Raspberrypi tool , Kernel sources.

   $ https://github.com/raspberrypi/tools.git

   $ git clone -b rpi-3.18.9-rt5 https://github.com/emlid/linux-rt-rpi.git

   $ cd Linux-rt-rpi

   step 2. Export the following variables to specify cross-compilation

   $ export ARCH=arm

   $ export CROSS_COMPILE=~/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf

   For Raspberry Pi 3:

   $ make bcm2709_rt_defconfig

   compile the kernel

   $ make -j5

   Install modules, will result in "lib" folder with modules and firmware:

   $ mkdir kernel-rt

   $ INSTALL_MOD_PATH=kernel-rt make modules_install

   Testing real-time capabilites using cyclictest utility

   git clone git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git

   cd rt-tests

   make all

   sudo cp ./cyclictest /usr/bin/

   cd ~

   sudo cyclictest -l1000000 -m -n -a0 -t1 -p99 -i400 -h400 -q

   RTOS for single processor Systems