MPLAB® Harmony v3 SD Card Audio Player/Reader Tutorial on PIC32 MZ EF MCUs

Objective

MPLAB^® Harmony provides the capability to quickly develop complex embedded systems that utilize multiple middleware stacks running at the same time in a Real-Time Operating System (RTOS) or non-RTOS system.

The rapid prototyping ability of MPLAB Harmony is due to the availability of software modules (Drivers, System Services, and Middleware Libraries) and tools (MPLAB Harmony 3 Configurator (MHC) and MPLAB Harmony Graphics Composer (MHGC)) that are designed to allow maximum reuse of code and rapid development.

The following exercises demonstrate the quick prototyping capability of MPLAB Harmony. These exercises should be completed sequentially to understand how the following exercise enhances and adds new functionality to the earlier exercise.

Two Ways to Use This Tutorial

1. Create the projects from scratch.
   • Use the provided source files and step-by-step instructions for each lab
2. Use the solution project as an example.
   • Build the solution project (found in the lab's firmware folder) and download it to the Multimedia Expansion Board II (MEB II) board to observe the expected behavior

Lab Objective

• Create an MPLAB X IDE Harmony project for a PIC32 microcontroller from scratch
• Use MHC to configure and generate Harmony code
• Create new application states and variables for Harmony projects
• Identify the proper place to add your application code to the Harmony project
• Demonstrate the use of Harmony peripheral libraries and drivers to control PIC32 peripherals (SPI, I²C, Timers, etc.)
• Demonstrate the use of Harmony middleware libraries (USB, FS, and Graphics, etc.)

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Reference Materials

• MPLAB^® REAL ICE™ In-Circuit Emulator
• PIC32MZ Embedded Connectivity with FPU Starter Kit
• PIC32 Multimedia Expansion Board II (v5) For PIC32 Starter Kits
• MPLAB^® X Integrated Development Environment
• MPLAB^® XC32 C/C++ Compiler
• MPLAB^® Harmony 3.xx Integrated Software Framework

Select Tools > Embedded > MPLAB Harmony 3 Framework Downloader in MPLAB to download the Harmony 3 modules.

Each module can also be downloaded directly from GitHub. The following is the list of modules required by this series of labs:

• DEV_PACKS v3.5.0
• MHC v3.3.2
• CORE v3.5.0
• CSP v3.5.0
• BSP v3.5.0
• AUDIO v3.4.0
• GFX v3.4.0
• TOUCH v3.4.0
• USB v3.3.0

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Apart from the hardware tools listed above, the following items are required to play audio from an SD card and to load audio files into the SD card over a USB interface from the PC:

• Wired stereo headphone
• Micro SD card containing audio files in waveform audio format (WAV)
• USB Type-A male to Micro-B male cable for SD card reader functionality
• USB Type-A male to Mini-B male cable for programming/debugging with PKOB

Harmony SD Card Audio Player/Reader Labs

The associated ZIP file contains the completed solution of these five labs. The completed solution is not needed to develop the labs from scratch; it can be used as an example and requires no modifications. To gain a deeper understanding of how to use the MPLAB Harmony framework for Quick Audio Prototyping, and creating an SD card Audio Player/Reader, we recommend you follow the step-by-step procedures detailed in the "Procedure" section that follows.

• Lab 1: Audio-Tone Generation Using a Lookup Table
• Lab 2: Audio-Tone Generation Using Text File Stored in SD Card
• Lab 3: SD Card Reader Support to Load Audio Files
• Lab 4: Play WAV Audio File from SD Card
• Lab 5: Display Graphics Support to Select and Play an Audio File

Lab Source Files and Solutions

These ZIP files contain the completed solution projects for all the labs associated with this SD card audio player tutorial. It also contains the source files needed to perform the labs per the following step-by-step instructions (see the "Procedure" section on this page).

​Unzip the contents of this ZIP file to a working folder of your choice. The following lab examples in this series use the <Any directory of your choice>/apps/training/solutions/audio_player/ directory.

(Example Directory = C:/microchip/harmony3/)

Download the ZIP file for each of these labs

• Lab1
• Lab2
• Lab3
• Lab4
• Lab5

Extracting the ZIP file will create the following folders:

• audio_player_labx (where x = 1 through 5) contains five lab folders (in the firmware folders) and source files (in the dev_files folders).
  • dev_files contains application source files and other support files (if any) required to perform each lab (see the "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

The exercise is split into five labs. Each lab progressively moves towards achieving the final goal of creating a complete audio solution using Harmony:

1. Lab 1: Audio-Tone Generation Using a Lookup Table
2. Lab 2: Audio-Tone Generation Using Text File Stored in SD Card
3. Lab 3: SD Card Reader Support to Load Audio Files
4. Lab 4: Play WAV Audio File from SD Card
5. Lab 5: Display Graphics Support to Select and Play Audio File

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Results

You will observe the following at the end of each lab:

• Lab 1: You should be able to hear a sine tone output through the headphone jack on the MEB II
• Lab 2: As in Lab 1, you should be able to hear a sine tone output through the headphone jack on the MEB II
• Lab 3: You should be able to load audio files to the SD card by connecting the MEB II to a PC over the USB interface. The MEB II will act as a USB Mass Storage Device​

• Lab 4: You should be able to play, and hear audio tracks (WAV files) played on your headphones connected to the MEB II
• Lab 5: You should see a graphical user interface on the MEB II display, populated with a list of audio tracks (WAV files) read from the SD card, along with volume and mute control. The user interface should respond to touch events and you should be able to select random tracks for playback, adjust the volume level and mute/unmute the audio output

Problems with the results of each lab could occur if you don't carefully follow the detailed steps provided. Also, note that each lab is an extension of the previous lab; successful completion of earlier labs is essential for the following labs to work.

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Analysis

In this exercise series, we have successfully developed an audio solution right from the basic tone playback to an SD card audio player. We added graphics display support and also added support for an SD card reader. Using MHC we configured the hardware modules including Clock, CODEC driver, Reference clock for the CODEC, I²S driver, SPI driver, SD card driver, GFX library, and USB Library. Each of the lab applications was developed in a state-based, loosely coupled implementation. The state-based implementation and lose coupling enabled easily enhancing subsequent labs.

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Conclusions

By the end of this lab series, you will have successfully developed a fairly complex audio solution in a fairly short time. By now you should appreciate the real power of MPLAB Harmony, particularly the power of MHC and the ease with which it allows you to add/remove software modules to an existing developed application. With this lab series completed, you are now in the position to create complex applications using PIC32 microcontrollers. MPLAB Harmony provides all the necessary software tools that will enable you to quickly develop your application. If you want to expand on this exercise series, try adding more software components such as the TCP/IP stack, or add application support for audio recording.

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