audiocore: Use constant for MP3 frame size

software/src/audiocore/audiocore.c

@@ -7,6 +7,8 @@
 
 #include "py/mperrno.h"
 
+_Static_assert(MP3_FRAME_SIZE == I2S_DMA_BUF_SIZE, "i2s buffer size must match MP3 frame size");
+
 void __time_critical_func(volume_adjust)(int16_t *buf, size_t samples, uint16_t scalef)
 {
     for (size_t pos = 0; pos < samples; ++pos) {
@@ -87,7 +89,7 @@ void __time_critical_func(core1_main)(void)
                     i2s_play(samplerate);
                     playing = true;
                 }
-                volume_adjust((int16_t *)buf, 2304, current_volume);
+                volume_adjust((int16_t *)buf, MP3_FRAME_SIZE * 2, current_volume);
                 i2s_commit_buf(buf);
                 send_consume_notify();
                 continue;

software/src/audiocore/mp3.c

@@ -72,7 +72,7 @@ static void __time_critical_func(mp3_consume_data)(size_t bytes_used)
     spin_unlock(shared_context.lock, flags);
 }
 
-bool __time_critical_func(mp3_decode)(uint32_t pcm_buf[static 1152], unsigned *samplerate)
+bool __time_critical_func(mp3_decode)(uint32_t pcm_buf[static MP3_FRAME_SIZE], unsigned *samplerate)
 {
     unsigned char *readptr;
     size_t bytes_avail = mp3_get_continuous_data(&readptr);
@@ -124,7 +124,7 @@ bool __time_critical_func(mp3_decode)(uint32_t pcm_buf[static 1152], unsigned *s
 #endif
     *samplerate = info.samprate;
 
-    if (info.outputSamps != 2304) {
+    if (info.outputSamps != MP3_FRAME_SIZE * 2) {
 #ifdef MP3_DEBUG
         printf("Unexpected number of output samples: %d\n", info.outputSamps);
 #endif

software/src/audiocore/mp3.h

@@ -6,9 +6,11 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+#define MP3_FRAME_SIZE 1152
+
 bool mp3_init(void);
 void mp3_deinit(void);
 
-bool mp3_decode(uint32_t pcm_buf[static 1152], unsigned *samplerate);
+bool mp3_decode(uint32_t pcm_buf[static MP3_FRAME_SIZE], unsigned *samplerate);
 
 void mp3_reset(void);