To port the Adafruit MP3 library to a different microcontroller, we first need to make sure the helix player can support it. Open the file mp3dec.h and if necessary add an #elif to the switch at the top of the file for your platform.

Next open the file assembly.h and if necessary add an #elif with some assembly code for the required functions:

static __inline int MULSHIFT32(int x, int y);
static __inline int FASTABS(int x);
static __inline int CLZ(int x);
static __inline Word64 MADD64(Word64 sum64, int x, int y);
static __inline Word64 SAR64(Word64 x, int n);

where Word64 is:

typedef signed long long int    Word64;  // 64-bit signed integer.

Adafruit_MP3 class modifications

The Adafruit_MP3 library uses a timer to control playback. This timer should be able to fire at least 44,100 times per second.

Because different microcontroller platforms implement timers differently, you will need to add an #elif to the timer functions in Adafruit_MP3.cpp with instructions on how to configure, enable, and disable timers on your microcontroller platform.

These functions are:

//enable the playback timer
static inline void enableTimer();

//disable the playback timer
static inline void disableTimer();

//configure the playback timer. Make sure to enable the interrupt.
static inline void configureTimer();

//if necessary, clear the interrupt flag.
static inline void acknowledgeInterrupt();

You may also need to redefine the name of the interrupt handler that the timer triggers. This is done in Adafruit_MP3.h. For example, on the SAMD51 (the chip that the Metro / Feather M4 uses), this is done with:

#define MP3_Handler TC2_Handler

This guide was first published on Nov 09, 2017. It was last updated on Mar 08, 2024.

This page (Porting to different microcontrollers) was last updated on Nov 09, 2017.

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