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FreeRTOS: LED Blinking And Button Polling

FreeRTOS is one of the most widely used open-source real-time operating systems (RTOS). In this article, we will look at a very simple FreeRTOS program: a push-button will enable/disable the blinking of an LED. The program is developed and tested using the LPCXpresso54102 board with NXP's LPC54102 microcontroller. The program can be easily adapted for

2020-10-20T23:58:11+03:00By |Categories: Embedded Systems|Tags: , |0 Comments

Using Callbacks in Firmware Development

In its classic form, a callback (aka callback function) is a function that is passed as an argument to another function. The function that accepts the callback as an argument is expected to call back on it (execute it) at a certain point in time. The callback mechanism allows a lower-level software layer to call

2020-10-05T09:01:21+03:00By |Categories: Embedded Systems|Tags: , |0 Comments

Aligned and Unaligned Memory Access

Unaligned memory access is the access of data with a size of N number of bytes from an address that is not evenly divisible by the number of bytes N. If the address is evenly divisible by N, we have aligned memory access. We can express this as Address/N, where Address is the memory address

2020-07-19T16:56:39+03:00By |Categories: Embedded Systems|Tags: , |0 Comments

Little-Endian vs Big-Endian in Embedded Systems

To better understand the concept of little-endian and big-endian formats we first have to look at how memory is accessed. The memory space of a microprocessor is expected to be byte-addressable. When a CPU has a 32-bit address bus this means that it can access a total of 232 addresses each with a size of

2020-06-07T21:07:09+03:00By |Categories: Embedded Systems|Tags: , |0 Comments

Peripheral Access Layer for Microcontrollers

The peripheral access layer is a layer of the firmware that provides access to the registers of a microcontroller's peripheral units. It has to be easy to use, well structured, and efficient. This layer is part of the software packages every microcontroller vendor provides for free with their Software Development Kits (SDK) and Integrated Development

2020-04-26T14:42:59+03:00By |Categories: Embedded Systems|Tags: , |0 Comments

RTOS: Mutex and Semaphore Basics

Designing an embedded system that employs a real-time operating system (RTOS) with multitasking behavior means that there will be resources that must be shared between the tasks. These shared resources (e.g peripheral modules, data structures, communication interfaces, etc.) by their nature do not support multiple concurrent accesses. Accessing them without any rules in place may

2020-03-16T06:18:21+02:00By |Categories: Embedded Systems|Tags: , , |0 Comments

Exception Context Switching on ARM Cortex-M

This article is a natural extension on the topics we covered in Function Calls on ARM Cortex-M Microprocessors. Due to the hardware specifics of the Cortex-M architecture, there is actually a lot of common in how function calls and exceptions are handled. The good thing for us as developers is that all exception handlers can

2020-02-24T07:20:40+02:00By |Categories: Embedded Systems|Tags: , |0 Comments

STM32 Bootloader Design – Part 3

Here is the bootloader code, let's go through it and explain it step by step: /* Includes ------------------------------------------------------------------*/ #include "main.h" #include "flash.h" #include "srecord.h" #define USER_APPLICATION_BASE_ADDRESS 0x8004000U uint8_t srec_data[16]; void __svc(1) EnablePrivilegedMode(void ); void __SVC_1 (void){ __disable_irq(); __set_CONTROL((__get_CONTROL( ))& 0xFFFFFFFE); // enter priv mode __enable_irq(); } static void BootJump(uint32_t *Address) { /* 1. Make sure,

2020-02-17T18:37:00+02:00By |Categories: Embedded Systems|Tags: , |0 Comments

RTOS Task Context Switching

In our article covering the scheduling algorithms of real-time operating systems (RTOS), we stated that they can run tasks in such a way that leaves the impression of a multitasking behavior. This is achieved by giving the RTOS the capability to interrupt a currently executing task and to start executing another one. At some point

2020-01-06T05:50:26+02:00By |Categories: Embedded Systems|Tags: , , |0 Comments

RTOS Scheduling Algorithms

We already introduced the basic concepts of real-time operating systems (RTOS) and now we will take a deeper look into one of the most important things when designing an embedded system using an RTOS - the scheduling of the tasks and the algorithms that are used. Scheduling Process Scheduling is the process of deciding which

2019-12-10T20:49:41+02:00By |Categories: Embedded Systems|Tags: , , |0 Comments
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