MP3Decoder: make testable in coverage build

An mp3 decoder (note that this needs `audiocore.get_buffer`, not
enabled on devices):
```py
import sys
import audiomp3
import audiocore

GET_BUFFER_DONE, GET_BUFFER_MORE_DATA, GET_BUFFER_ERROR = range(3)

with audiomp3.MP3Decoder(sys.argv[1]) as decoder, open(sys.argv[2], "wb") as target:

    while True:
        res, samples = audiocore.get_buffer(decoder)
        if res != GET_BUFFER_ERROR:
            target.write(samples)
        if res != GET_BUFFER_MORE_DATA:
            break
```

this doesn't actually add any tests though

Author: jepler

ports/unix/variants/coverage/mpconfigvariant.mk

@@ -34,6 +34,8 @@ SRC_BITMAP := \
 	shared-bindings/audiomixer/__init__.c \
 	shared-bindings/audiomixer/Mixer.c \
 	shared-bindings/audiomixer/MixerVoice.c \
+	shared-bindings/audiomp3/__init__.c \
+	shared-bindings/audiomp3/MP3Decoder.c \
 	shared-bindings/bitmapfilter/__init__.c \
 	shared-bindings/bitmaptools/__init__.c \
 	shared-bindings/codeop/__init__.c \
@@ -62,6 +64,7 @@ SRC_BITMAP := \
 	shared-module/audiocore/RawSample.c \
 	shared-module/audiocore/WaveFile.c \
 	shared-module/audiomixer/__init__.c \
+	shared-module/audiomp3/MP3Decoder.c \
 	shared-module/audiomixer/Mixer.c \
 	shared-module/audiomixer/MixerVoice.c \
 	shared-module/bitmapfilter/__init__.c \
@@ -88,10 +91,32 @@ SRC_BITMAP := \
 
 SRC_C += $(SRC_BITMAP)
 
+SRC_C += $(addprefix lib/mp3/src/, \
+        bitstream.c \
+        buffers.c \
+        dct32.c \
+        dequant.c \
+        dqchan.c \
+        huffman.c \
+        hufftabs.c \
+        imdct.c \
+        mp3dec.c \
+        mp3tabs.c \
+        polyphase.c \
+        scalfact.c \
+        stproc.c \
+        subband.c \
+        trigtabs.c \
+)
+
+$(BUILD)/lib/mp3/src/buffers.o: CFLAGS += -include "shared-module/audiomp3/__init__.h" -D'MPDEC_ALLOCATOR(x)=malloc(x)' -D'MPDEC_FREE(x)=free(x)' -fwrapv
+
 CFLAGS += \
 	-DCIRCUITPY_AESIO=1 \
 	-DCIRCUITPY_AUDIOCORE=1 \
 	-DCIRCUITPY_AUDIOMIXER=1 \
+	-DCIRCUITPY_AUDIOMP3=1 \
+	-DCIRCUITPY_AUDIOMP3_USE_PORT_ALLOCATOR=0 \
 	-DCIRCUITPY_AUDIOCORE_DEBUG=1 \
 	-DCIRCUITPY_BITMAPTOOLS=1 \
 	-DCIRCUITPY_CODEOP=1 \

shared-bindings/audiomp3/MP3Decoder.c

@@ -137,13 +137,15 @@ static mp_obj_t audiomp3_mp3file_obj_get_file(mp_obj_t self_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(audiomp3_mp3file_get_file_obj, audiomp3_mp3file_obj_get_file);
 
-static mp_obj_t audiomp3_mp3file_obj_set_file(mp_obj_t self_in, mp_obj_t file) {
+static mp_obj_t audiomp3_mp3file_obj_set_file(mp_obj_t self_in, mp_obj_t stream) {
     audiomp3_mp3file_obj_t *self = MP_OBJ_TO_PTR(self_in);
     check_for_deinit(self);
-    if (!mp_obj_is_type(file, &mp_type_fileio)) {
+    const mp_stream_p_t *stream_p = mp_get_stream_raise(stream, MP_STREAM_OP_READ);
+
+    if (stream_p->is_text) {
         mp_raise_TypeError(MP_ERROR_TEXT("file must be a file opened in byte mode"));
     }
-    common_hal_audiomp3_mp3file_set_file(self, file);
+    common_hal_audiomp3_mp3file_set_file(self, stream);
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_2(audiomp3_mp3file_set_file_obj, audiomp3_mp3file_obj_set_file);

shared-module/audiomp3/MP3Decoder.c

@@ -23,6 +23,12 @@
 
 #define MAX_BUFFER_LEN (MAX_NSAMP * MAX_NGRAN * MAX_NCHAN * sizeof(int16_t))
 
+#if defined(MICROPY_UNIX_COVERAGE)
+#define background_callback_prevent() ((void)0)
+#define background_callback_allow() ((void)0)
+#define background_callback_add(buf, fn, arg) ((fn)((arg)))
+#endif
+
 // (near copy of mp_stream_posix_read, but with changes)
 // (circuitpy doesn't enable posix stream routines anyway)
 STATIC ssize_t stream_read(void *stream, void *buf, size_t len) {
@@ -42,7 +48,8 @@ STATIC ssize_t stream_read(void *stream, void *buf, size_t len) {
 
 // (near copy of mp_stream_posix_read, but with changes)
 // (circuitpy doesn't enable posix stream routines anyway)
-STATIC ssize_t stream_read_all(void *stream, void *buf, size_t len) {
+// (and the return value semantic is different)
+STATIC ssize_t stream_read_all(void *stream, uint8_t *buf, size_t len) {
     ssize_t total_read = 0;
     while (len) {
         ssize_t r = stream_read(stream, buf, len);
@@ -170,7 +177,7 @@ static void mp3file_skip_id3v2(audiomp3_mp3file_obj_t *self) {
         (data[9] & 0x80) == 0)) {
         return;
     }
-    uint32_t size = (data[6] << 21) | (data[7] << 14) | (data[8] << 7) | (data[9]);
+    int32_t size = (data[6] << 21) | (data[7] << 14) | (data[8] << 7) | (data[9]);
     size += 10; // size excludes the "header" (but not the "extended header")
     // First, deduct from size whatever is left in buffer
     uint32_t to_consume = MIN(size, BYTES_LEFT(self));

shared-module/audiomp3/MP3Decoder.h

@@ -18,8 +18,8 @@ typedef struct {
     struct _MP3DecInfo *decoder;
     background_callback_t inbuf_fill_cb;
     uint8_t *inbuf;
-    uint32_t inbuf_length;
-    uint32_t inbuf_offset;
+    int32_t inbuf_length;
+    int32_t inbuf_offset;
     int16_t *buffers[2];
     uint32_t len;
     uint32_t frame_buffer_size;