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
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