Multitasking on Raspberry Pi using Execve and Fork Commands

The advantage of having an Operating System running on a microcontroller board other than simple embedded c code is Multitasking. The Raspberrypi is a microcontroller board which is powerful enough to run large operating systems like Linux, Mac and Windows. The Raspberrypi is a microcontroller board which runs on a SoC chip from the Broadcom with ARM11 processor at the core. The Board is a mini computer itself without any input or output devices but ports provided to connect them.

The Raspberrypi is called a mini-computer because the SoC has the powerful ARM11 processor which runs on 700 MHz at its core and having the peripherals like timers, interrupt controller, GPIO, PCM / I2S, DMA controller, I2C, SPI slave, PWM, UART, USB, graphical processing unit (GPU) which includes VideoCore, MPEG-2 and MPEG-4 and a 512 MB SDRAM. There is an Ethernet port which can be used to connect the board to a computer network. Those who don’t want to use a HDTV and separate keyboard and mouse for the Rspberrypi board can plug the board using a LAN cable to the Ethernet port of the PC and do remote access in TUI or GUI mode.

Multitasking on Raspberry Pi using Execve and Fork Commands

The term ‘Process’ refers to the piece of code which is currently in execution. The fork () is a function which can be used in the C code to start a new process as a ‘Child process’. The process or the code which is in execution which makes a call to the function fork () is called the ‘Parent process’ and the new process created by the fork () is called a ‘Child process’. The ‘Parent process’ and the ‘Child process’ executes parallel (high speed processor makes it feel like parallel processing) and independently and thus achieves multi-tasking. The fork () most of the time uses the execve () function to create a new process as Child.

In this project the Raspberrypi board is loaded with Ubuntu and is remotely accessed using VNC. The Raspberrypi board is also connected to the internet. There are 26 connectors which can be taken out from the connector port of the Raspberrypi board. All the connector pins are taken out using 13*2 pin female connectors and at the other end of their wire 26 pin Burg stick male connectors are attached. The Burg stick male connectors allow each pin out from the Raspberrypi board to be plugged into the holes of a breadboard.  To access the pins that coming out of the Broadcom controller of the Raspberrypi board using C language, a C library is available called “bcm2835” which has been downloaded and installed.

There are eight general purpose IO pins on the 13*2 pin connectors of the Raspberrypi board and to each one of them a LED is connected through 1K resistor. Separate code has been written to blink the LEDs individually and made them into executable files named blink2, blink3, blink4, blink5, blink6, blink7 and blink8. It is suggested to keep all the .c files and the executable files in a single folder for this particular project.

The user can run any of the LED blinking programs from the command line. For example to execute the file ‘blink1’, the user can use the following command;

./blink1

The user can perform multi-tasking on them by entering the following commands one after the other. The user can perform multi-tasking with the eight LED codes by entering the following eight commands one after the other.

 

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