Add a manual test of synthio

this allows to test how the midi synthesizer is working, without access
to hardware. Run `micropython-coverage midi2wav.py` and it will create
`tune.wav` as an output.

Author: jepler

tests/circuitpython-manual/synthio/wave/.gitignore

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+tune.wav

tests/circuitpython-manual/synthio/wave/README.md

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+# Test synthio without hardware
+
+Build the uninx port then run `....../ports/unix/micropython-coverage midi2wav.py`.
+
+This will create `tune.wav` as output, which you can listen to using any old audio player.

tests/circuitpython-manual/synthio/wave/audioop.py

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+import struct
+
+
+def byteswap(data, sampwidth):
+    print(data)
+    raise
+    ch = "I" if sampwidth == 16 else "H"

tests/circuitpython-manual/synthio/wave/chunk.py

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+"""Simple class to read IFF chunks.
+
+An IFF chunk (used in formats such as AIFF, TIFF, RMFF (RealMedia File
+Format)) has the following structure:
+
++----------------+
+| ID (4 bytes)   |
++----------------+
+| size (4 bytes) |
++----------------+
+| data           |
+| ...            |
++----------------+
+
+The ID is a 4-byte string which identifies the type of chunk.
+
+The size field (a 32-bit value, encoded using big-endian byte order)
+gives the size of the whole chunk, including the 8-byte header.
+
+Usually an IFF-type file consists of one or more chunks.  The proposed
+usage of the Chunk class defined here is to instantiate an instance at
+the start of each chunk and read from the instance until it reaches
+the end, after which a new instance can be instantiated.  At the end
+of the file, creating a new instance will fail with an EOFError
+exception.
+
+Usage:
+while True:
+    try:
+        chunk = Chunk(file)
+    except EOFError:
+        break
+    chunktype = chunk.getname()
+    while True:
+        data = chunk.read(nbytes)
+        if not data:
+            pass
+        # do something with data
+
+The interface is file-like.  The implemented methods are:
+read, close, seek, tell, isatty.
+Extra methods are: skip() (called by close, skips to the end of the chunk),
+getname() (returns the name (ID) of the chunk)
+
+The __init__ method has one required argument, a file-like object
+(including a chunk instance), and one optional argument, a flag which
+specifies whether or not chunks are aligned on 2-byte boundaries.  The
+default is 1, i.e. aligned.
+"""
+
+
+class Chunk:
+    def __init__(self, file, align=True, bigendian=True, inclheader=False):
+        import struct
+
+        self.closed = False
+        self.align = align  # whether to align to word (2-byte) boundaries
+        if bigendian:
+            strflag = ">"
+        else:
+            strflag = "<"
+        self.file = file
+        self.chunkname = file.read(4)
+        if len(self.chunkname) < 4:
+            raise EOFError
+        try:
+            self.chunksize = struct.unpack_from(strflag + "L", file.read(4))[0]
+        except struct.error:
+            raise EOFError from None
+        if inclheader:
+            self.chunksize = self.chunksize - 8  # subtract header
+        self.size_read = 0
+        try:
+            self.offset = self.file.tell()
+        except (AttributeError, OSError):
+            self.seekable = False
+        else:
+            self.seekable = True
+
+    def getname(self):
+        """Return the name (ID) of the current chunk."""
+        return self.chunkname
+
+    def getsize(self):
+        """Return the size of the current chunk."""
+        return self.chunksize
+
+    def close(self):
+        if not self.closed:
+            try:
+                self.skip()
+            finally:
+                self.closed = True
+
+    def isatty(self):
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        return False
+
+    def seek(self, pos, whence=0):
+        """Seek to specified position into the chunk.
+        Default position is 0 (start of chunk).
+        If the file is not seekable, this will result in an error.
+        """
+
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        if not self.seekable:
+            raise OSError("cannot seek")
+        if whence == 1:
+            pos = pos + self.size_read
+        elif whence == 2:
+            pos = pos + self.chunksize
+        if pos < 0 or pos > self.chunksize:
+            raise RuntimeError
+        self.file.seek(self.offset + pos, 0)
+        self.size_read = pos
+
+    def tell(self):
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        return self.size_read
+
+    def read(self, size=-1):
+        """Read at most size bytes from the chunk.
+        If size is omitted or negative, read until the end
+        of the chunk.
+        """
+
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        if self.size_read >= self.chunksize:
+            return b""
+        if size < 0:
+            size = self.chunksize - self.size_read
+        if size > self.chunksize - self.size_read:
+            size = self.chunksize - self.size_read
+        data = self.file.read(size)
+        self.size_read = self.size_read + len(data)
+        if self.size_read == self.chunksize and self.align and (self.chunksize & 1):
+            dummy = self.file.read(1)
+            self.size_read = self.size_read + len(dummy)
+        return data
+
+    def skip(self):
+        """Skip the rest of the chunk.
+        If you are not interested in the contents of the chunk,
+        this method should be called so that the file points to
+        the start of the next chunk.
+        """
+
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        if self.seekable:
+            try:
+                n = self.chunksize - self.size_read
+                # maybe fix alignment
+                if self.align and (self.chunksize & 1):
+                    n = n + 1
+                self.file.seek(n, 1)
+                self.size_read = self.size_read + n
+                return
+            except OSError:
+                pass
+        while self.size_read < self.chunksize:
+            n = min(8192, self.chunksize - self.size_read)
+            dummy = self.read(n)
+            if not dummy:
+                raise EOFError

tests/circuitpython-manual/synthio/wave/midi2wav.py

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+import audiocore
+import synthio
+from ulab import numpy as np
+import wave
+
+SAMPLE_SIZE = 1024
+VOLUME = 32700
+sine = np.array(
+    np.sin(np.linspace(0, 2 * np.pi, SAMPLE_SIZE, endpoint=False)) * VOLUME,
+    dtype=np.int16,
+)
+
+envelope = synthio.Envelope(
+    attack_time=0.1, decay_time=0.05, release_time=0.2, attack_level=1, sustain_level=0.8
+)
+melody = synthio.MidiTrack(
+    b"\0\x90H\0*\x80H\0\6\x90J\0*\x80J\0\6\x90L\0*\x80L\0\6\x90J\0"
+    + b"*\x80J\0\6\x90H\0*\x80H\0\6\x90J\0*\x80J\0\6\x90L\0T\x80L\0"
+    + b"\x0c\x90H\0T\x80H\0\x0c\x90H\0T\x80H\0",
+    tempo=240,
+    sample_rate=48000,
+    waveform=sine,
+    envelope=envelope,
+)
+
+# sox -r 48000 -e signed -b 16 -c 1 tune.raw tune.wav
+with wave.open("tune.wav", "w") as f:
+    f.setnchannels(1)
+    f.setsampwidth(2)
+    f.setframerate(48000)
+    while True:
+        result, data = audiocore.get_buffer(melody)
+        if data is None:
+            break
+        f.writeframes(data)
+        if result != 1:
+            break
+
+melody = synthio.MidiTrack(
+    b"\0\x90H\0*\x80H\0\6\x90J\0*\x80J\0\6\x90L\0*\x80L\0\6\x90J\0"
+    + b"*\x80J\0\6\x90H\0*\x80H\0\6\x90J\0*\x80J\0\6\x90L\0T\x80L\0"
+    + b"\x0c\x90H\0T\x80H\0\x0c\x90H\0T\x80H\0",
+    tempo=240,
+    sample_rate=48000,
+    waveform=sine,
+)
+
+# sox -r 48000 -e signed -b 16 -c 1 tune.raw tune.wav
+with wave.open("tune-noenv.wav", "w") as f:
+    f.setnchannels(1)
+    f.setsampwidth(2)
+    f.setframerate(48000)
+    while True:
+        result, data = audiocore.get_buffer(melody)
+        if data is None:
+            break
+        f.writeframes(data)
+        if result != 1:
+            break