Add non-blocking playback method

src/VS1053.cpp

@@ -77,6 +77,30 @@ void VS1053::sdi_send_buffer(uint8_t *data, size_t len) {
     data_mode_off();
 }
 
+size_t VS1053::sdi_send_buffer_non_blocking(const uint8_t *data, size_t limit) {
+    size_t iocount = 0;
+
+    data_mode_on();
+    while (digitalRead(dreq_pin) && limit > 0) // More to do?
+    {
+        size_t chunk_length = limit;
+        if (chunk_length > vs1053_chunk_size) {
+            chunk_length = vs1053_chunk_size;
+        }
+
+        spi_write_bytes(data, chunk_length);
+
+        data += chunk_length;
+        limit -= chunk_length;
+        iocount += chunk_length;
+
+        yield();
+    }
+    data_mode_off();
+
+    return iocount;
+}
+
 void VS1053::sdi_send_fillers(size_t len) {
     size_t chunk_length; // Length of chunk 32 byte or shorter
 
@@ -244,6 +268,10 @@ void VS1053::playChunk(uint8_t *data, size_t len) {
     sdi_send_buffer(data, len);
 }
 
+size_t VS1053::playNonBlocking(const uint8_t *data, size_t limit) {
+    return sdi_send_buffer_non_blocking(data, limit);
+}
+
 void VS1053::stopSong() {
     uint16_t modereg; // Read from mode register
     int i;            // Loop control

src/VS1053.h

@@ -117,6 +117,8 @@ class VS1053 {
 
     void sdi_send_buffer(uint8_t *data, size_t len);
 
+    size_t sdi_send_buffer_non_blocking(const uint8_t *data, size_t limit);
+
     void sdi_send_fillers(size_t length);
 
     void wram_write(uint16_t address, uint16_t data);
@@ -136,6 +138,10 @@ class VS1053 {
     // Play a chunk of data.  Copies the data to the chip.  Blocks until complete
     void playChunk(uint8_t *data, size_t len);
 
+    // Writes the up to limit bytes from the given buffer to the VS1053 audio buffer. Tries to write as many bytes
+    // as possible with out blocking. Returns the number of bytes written.
+    size_t playNonBlocking(const uint8_t *data, size_t limit);
+
     // Finish playing a song. Call this after the last playChunk call
     void stopSong();