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Getting Started with MPLAB® Harmony v3 Drivers on SAM C21 MCUs Using FreeRTOS™

Last modified by Microchip on 2024/06/24 06:31

Objective

MPLAB® Harmony v3 is a flexible, fully integrated embedded software development framework for 32-bit MCUs and MPUs.

MPLAB Harmony v3 includes the MPLAB Code Configurator (MCC) tool, a set of modular devices, and middleware libraries. Additionally, there are numerous example applications, all of which are designed to help the developers quickly and easily develop powerful and efficient embedded software for Microchip’s 32-bit PIC® and SAM devices.

This tutorial shows you how to use MCC to create an application that gets you started in developing applications on SAM C21 MCUs using the MPLAB Harmony v3 software framework FreeRTOS™.

Contents

​In this tutorial, you will use Arm® Cortex® Microcontroller Software Interface Standard - Real-Time Operating System (CMSIS-RTOS) adoption of FreeRTOS version 10.4.6. FreeRTOS is a market-leading real-time operating system for microcontrollers having ports for Microchip’s microcontrollers. The FreeRTOS kernel is released under the MIT open-source license.

MPLAB Harmony v3 Drivers support Asynchronous and Synchronous modes of operation.

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Asynchronous Mode

  • Non-blocking Application Program Interfaces (APIs)
  • Works seamlessly in bare-metal and RTOS environments
  • Interrupt and thread-safe

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Synchronous Mode

  • Blocking APIs
  • Suitable for use in RTOS environment
  • Interrupt and thread-safe
  • Blocking API: A blocking API hangs up execution flow until it has performed its function and returns a result.
  • Non-blocking API: Non-blocking API receives the application request and returns immediately without providing the result. The result of the non-blocking API call is provided separately through an asynchronous event. The application verifies the event to take further action.
  • Interrupt-safe: A sequence of code is said to be “interrupt-safe” when the occurrence of an interrupt(s) doesn't alter the output or functional behavior of the code. To be "interrupt-safe," the sequence of code in consideration must be atomic (indivisible and uninterruptible), and the relevant interrupts must be disabled before entering the sequence.
  • Thread-safe: In an RTOS-based environment, a driver and its clients may each run in their own RTOS thread. If the RTOS is preemptive, the scheduler may interrupt any of these threads at any time and switch to another. If the other thread happens to also non-atomically access the same shared resource or executes the same critical section of code, that section of code must be guarded and made atomic. The sequence of code with such guards is known as “thread-safe” code.

In this tutorial, you will use MPLAB Harmony drivers in the Synchronous mode of operation.

The application makes use of the SAM C21 Xplained Pro Evaluation Kit and I/O1 Xplained Pro Extension Kit (sold separately).

The application reads the current room temperature from the temperature sensor on the I/O1 Xplained Pro Extension Kit. The temperature reading is displayed on a serial console periodically every second. Further, the application writes the temperature readings to EEPROM. When a character is entered on the console, the last five written temperature values are read from the EEPROM and displayed on the console. Also, an LED (LED0) is toggled every time the temperature is displayed on the serial console.

The application you create will utilize:

  • I²C Synchronous Driver to read the temperature from a temperature sensor and store/retrieve to/from EEPROM.
  • Universal Synchronous Asynchronous Receiver Transmitter (USART) Synchronous Driver to print the temperature values on a COM (serial) port terminal application running on a PC.
  • PORTS Peripheral Library to toggle an LED.
  • FreeRTOS library to create application threads and intercommunicate between application threads.

In the process, the lab will also demonstrate the use of callback functions.

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Two Ways to Use This Tutorial

  1. Create the project from scratch:
    • Use the provided source files and step-by-step instructions below.
  2. Use the solution project as an example:
    • Build the solution project and download it to the SAM C21 Xplained Pro Evaluation Kit Board to observe the expected behavior.

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Lab Objectives

  1. Create an MPLAB Harmony v3 project for a SAM C21 microcontroller from scratch.
  2. Use MCC to configure and generate MPLAB Harmony Synchronous Driver code for I²C and USART peripherals.
  3. Along with the configuration of drivers for I²C and USART peripherals, use MCC to configure and generate MPLAB Harmony v3 peripheral libraries for the I²C, USART, and PORTS peripherals.
  4. Use MCC to configure application threads using FreeRTOS.
  5. Use the MPLAB Harmony v3 Driver, Peripheral Library APIs, and FreeRTOS APIs to implement the application.

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Reference Materials

Hardware Tools

​The Xplained Pro series evaluation kits include an onboard Embedded Debugger (EDBG). No external tools are necessary to program or debug the ATSAMC21J18A. For programming/debugging, the EDBG connects to the host PC through the USB Micro-B connector on the SAM C21 Xplained Pro Evaluation Kit.

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Hardware Connection Setup

Hardware Setup

Figure: Hardware Setup

Hardware Connection Setup

Apart from the hardware tools listed above, the following items are required:

  • USB Type-A male to Micro-B male cable for programming/debugging.

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Connection Diagram

The application has the temperature sensor and EEPROM connected to the SAM C21 over the I²C interface and the console (serial terminal) on a PC connected over the USART interface (through USB to USART converter).

Connection Diagram

Figure: Connection Diagram

Note: Use the default address of 0x4F and 0x57 to access the temperature sensor (0x4F) and EEPROM (0x57) on the I/O1 Xplained Pro board.

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Software Tools

This project has been verified to work with the following versions of software tools:

  • MPLAB X IDE v6.10
  • MPLAB XC32/32++ Compiler v4.30
  • MPLAB Harmony CSP v3.17.0
  • DEV_PACKS v3.17.0
  • MPLAB Code Configurator Plugin v5.3.7
  • CORE v3.13.1
  • BSP v3.16.1
  • CMSIS_FreeRTOS v10.4.6

Because we regularly update our tools, occasionally you may discover an issue while using the newer versions. If you suspect that to be the case, we recommend that you double-check and use the same versions that the project was tested with.

Installers

Use the MPLAB Code Configurator (MCC) to download the repositories.

For this lab, you could download the following repositories from GitHub:

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Overview

This lab shows you how to create an MPLAB Harmony v3 project from scratch, configure, and generate:

  • MPLAB Harmony v3 Peripheral Libraries code for TC, I²C, USART, and PORTS peripherals
  • MPLAB Harmony v3 Synchronous Driver code for I²C and USART peripherals
  • MPLAB Harmony v3 application threads using FreeRTOS

It demonstrates the reading of temperature sensor values from the temperature sensor available on the I/O1 Xplained Pro Extension Kit periodically and displays it on a serial console. It further writes the temperature readings to EEPROM. When a character is entered on the console, the last five written temperature values are read from the EEPROM and displayed on the console. Also, an LED is toggled every time the temperature is displayed on the serial console.

The application functionality is divided into three threads.

  1. Sensor thread – To read and display temperature periodically.
  2. EEPROM thread – To write the temperature values to EEPROM and display it on the COM (serial) port terminal when requested by the user.
  3. User Input thread – To read the character entered on the COM (serial) port terminal.

The Sensor thread, EEPROM thread, and User Input thread run the corresponding application function in an infinite loop. These threads are created from the SYS_Tasks routine. Following the creation of these threads, the FreeRTOS scheduler is invoked. The scheduler performs the preemptive scheduling of these threads based on the waiting, ready, and running state of each of them. Developers can use MCC to generate the template files for the three application threads.

The Application Threads

Figure: The Application Threads

Once the scheduler is invoked, the threads start to run based on the default scheduling method (preemptive).

By default, the Sensor thread is blocked and wakes up every time the temperature sampling period expires. Once active, the Sensor thread reads the latest room temperature value from the temperature sensor and prints the same on the serial terminal. It also notifies the EEPROM thread through the RTOS queue of the availability of the latest temperature value which needs to be stored in EEPROM. Once notified, the Sensor threads block again for the temperature sampling period duration.

By default, the EEPROM thread is waiting for an event to occur. It wakes up when there is an event in the RTOS queue to either write the latest temperature value or the read last five temperature values. Based on the event, the EEPROM thread performs writing or reading and goes back to the waiting state.

By default, the User Input thread is blocked waiting to receive a character on the USART receive line. Once a character is received, the User Input thread becomes active and submits an EEPROM read request to the EEPROM thread through the RTOS queue to read the last five temperature values stored in EEPROM. After serving the user input request, the thread goes back to the blocking state to receive another character on the USART receive line.

The Application Thread Functioning

Figure: The Application Thread Functioning

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Lab Source Files and Solutions

This ZIP file contains the completed solution project for this lab. It also contains the source files needed to perform the lab as per the following step-by-step instructions (see the "Procedure" section).

​The contents of this ZIP file need to be placed in the folder below:
<Any directory of your choice>/training/
(example Directory = C:/microchip/harmony/v3_6_1)

Note:

  1. The project location of an MPLAB Harmony v3 project is independent of the location of the MPLAB Harmony Framework path (i.e., you do not need to create or place an MPLAB Harmony v3 project in a relative path under the Harmony v3 framework folder). The project can be created or placed in any directory of your choice.
  2. The point above is true because when created, an MPLAB Harmony v3 project generates all the referred source/header files and libraries (if any) under the project folder.
  3. Both points above contrast with the Harmony v2 project location. In Harmony v2, the project was supposed to be created in a location under the Harmony framework.

ZIP Files

Extracting the ZIP file creates the following folders:

  • samc21_getting_started_freertos contains the lab solution (in the firmware folder) and source files (in the dev_files folder).
    • dev_files contains subfolder sam_c21_xpro containing application source files and other support files (if any) required to perform the lab (see "Procedure" section).
    • firmware contains the completed lab solution project. It can be directly built and downloaded on the hardware to observe expected behavior.

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Procedure

​You must complete all of these steps before you can build, download, and run the application.

Lab Index

Step 1: Create a Project and Configure the SAM C21

  • Create MPLAB Harmony v3 Project using MPLAB X IDE
  • Verify Clock Settings

Step 2: Configure I²C and USART Drivers in Synchronous mode

  • Configure I²C Driver and I²C Pins
  • Configure USART Driver and USART Pins

Step 3: Configure Pin for LED

  • Configure LED Pin
  • Rename the Default Main File
  • Configure Application Threads

Step 4: Generate Code
Step 5: Add Application Code to the Project
Step 6: Build, Program, and Observe the Outputs

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