Add stereo support to usb_audio

shared-bindings/usb_audio/USBMicrophone.c

@@ -12,6 +12,7 @@
 #include "shared-bindings/usb_audio/USBMicrophone.h"
 #include "shared-bindings/util.h"
 #include "shared-module/usb_audio/__init__.h"
+#include "shared-module/usb_audio/usb_audio_descriptors.h"
 
 //| class USBMicrophone:
 //|     """Streams an audio sample to the host computer as a USB Audio Class microphone.

shared-bindings/usb_audio/__init__.c

@@ -19,9 +19,9 @@
 //| Audio Class (UAC2) microphone: the board is the audio *source* and streams
 //| samples to the host over a USB isochronous IN endpoint.
 //|
-//| This mode requires 1 IN endpoint and 2 interfaces. Generally, microcontrollers
-//| have a limit on the number of endpoints. If you exceed the number of endpoints,
-//| CircuitPython will automatically enter Safe Mode. Even in this case, you may be
+//| This mode requires 2 IN endpoints and 2 interfaces.
+//| Generally, microcontrollers have a limit on the number of endpoints. If you exceed the number
+//| of endpoints, CircuitPython will automatically enter Safe Mode. Even in this case, you may be
 //| able to enable USB audio by also disabling other USB functions, such as
 //| `usb_hid` or `usb_midi`.
 //|
@@ -32,7 +32,7 @@
 //|
 //|     # boot.py
 //|     import usb_audio
-//|     usb_audio.enable(sample_rate=16000, channel_count=1, bits_per_sample=16)
+//|     usb_audio.enable(sample_rate=16000, bits_per_sample=16)
 //|
 //| .. code-block:: py
 //|
@@ -61,9 +61,8 @@
 //|         pass
 //|     mic.stop()
 //|
-//| The ``sample_rate`` and ``channel_count`` of the sample played must match the
-//| values passed to `enable`, and the sample must be 16-bit signed; otherwise
-//| ``play`` raises a ``ValueError``.
+//| The ``sample_rate`` and ``channel_count`` of the sample played must match the values passed to `enable`,
+//| and the sample must be 16-bit signed; otherwise ``play`` raises a ``ValueError``.
 //|
 //| This interface is experimental and may change without notice even in stable
 //| versions of CircuitPython."""
@@ -84,7 +83,6 @@
 //| def enable(
 //|     sample_rate: int = 16000,
 //|     channel_count: int = 1,
-//|     bits_per_sample: int = 16,
 //|     microphone: bool = True,
 //|     speaker: bool = False,
 //| ) -> None:
@@ -93,7 +91,7 @@
 //|     This function may only be used from ``boot.py``.
 //|
 //|     :param int sample_rate: Samples per second of the streamed audio.
-//|     :param int channel_count: Number of channels. Only mono (1) is supported initially.
+//|     :param int channel_count: Number of channels. Either mono (1) or stereo (2) is supported.
 //|     :param int bits_per_sample: Bits per signed PCM sample. Only 16 is supported initially.
 //|     :param bool microphone: Present a microphone (audio flows board -> host). Enabled by default.
 //|     :param bool speaker: Present a speaker (audio flows host -> board).
@@ -103,11 +101,10 @@
 //|
 //|
 static mp_obj_t usb_audio_enable(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
-    enum { ARG_sample_rate, ARG_channel_count, ARG_bits_per_sample, ARG_microphone, ARG_speaker };
+    enum { ARG_sample_rate, ARG_channel_count, ARG_microphone, ARG_speaker };
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_sample_rate, MP_ARG_INT, { .u_int = 16000 } },
         { MP_QSTR_channel_count, MP_ARG_INT, { .u_int = 1 } },
-        { MP_QSTR_bits_per_sample, MP_ARG_INT, { .u_int = 16 } },
         { MP_QSTR_microphone, MP_ARG_BOOL, { .u_bool = true } },
         { MP_QSTR_speaker, MP_ARG_BOOL, { .u_bool = false } },
     };
@@ -116,15 +113,14 @@ static mp_obj_t usb_audio_enable(size_t n_args, const mp_obj_t *pos_args, mp_map
 
     mp_int_t sample_rate = mp_arg_validate_int_range(args[ARG_sample_rate].u_int, 1, USB_AUDIO_MAX_SAMPLE_RATE, MP_QSTR_sample_rate);
     mp_int_t channel_count = mp_arg_validate_int_range(args[ARG_channel_count].u_int, 1, USB_AUDIO_N_CHANNELS, MP_QSTR_channel_count);
-    mp_int_t bits_per_sample = mp_arg_validate_int(args[ARG_bits_per_sample].u_int, USB_AUDIO_BITS_PER_SAMPLE, MP_QSTR_bits_per_sample);
     bool microphone = args[ARG_microphone].u_bool;
     bool speaker = args[ARG_speaker].u_bool;
 
     if (!microphone && !speaker) {
         mp_raise_ValueError(MP_ERROR_TEXT("At least one of microphone and speaker must be enabled"));
     }
 
-    if (!shared_module_usb_audio_enable(sample_rate, channel_count, bits_per_sample, microphone, speaker)) {
+    if (!shared_module_usb_audio_enable(sample_rate, channel_count, microphone, speaker)) {
         mp_raise_RuntimeError(MP_ERROR_TEXT("Cannot change USB devices now"));
     }
 

shared-module/usb_audio/USBMicrophone.c

@@ -11,6 +11,7 @@
 
 #include "shared-bindings/usb_audio/USBMicrophone.h"
 #include "shared-module/usb_audio/__init__.h"
+#include "shared-module/usb_audio/usb_audio_descriptors.h"
 #include "shared-module/audiocore/__init__.h"
 
 // Only one microphone may feed the single USB IN endpoint at a time. This points
@@ -53,7 +54,7 @@ void common_hal_usb_audio_usbmicrophone_play(usb_audio_usbmicrophone_obj_t *self
     if (audiosample_get_channel_count(sample_base) != usb_audio_channel_count) {
         mp_raise_ValueError_varg(MP_ERROR_TEXT("The sample's %q does not match"), MP_QSTR_channel_count);
     }
-    if (audiosample_get_bits_per_sample(sample_base) != usb_audio_bits_per_sample) {
+    if (audiosample_get_bits_per_sample(sample_base) != USB_AUDIO_BITS_PER_SAMPLE) {
         mp_raise_ValueError_varg(MP_ERROR_TEXT("The sample's %q does not match"), MP_QSTR_bits_per_sample);
     }
     if (!sample_base->samples_signed) {
@@ -101,15 +102,33 @@ bool common_hal_usb_audio_usbmicrophone_get_paused(usb_audio_usbmicrophone_obj_t
     return self->playing && self->paused;
 }
 
+static inline uint32_t copy16lsb(uint32_t val) {
+    #if (defined(__ARM_ARCH_7EM__) && (__ARM_ARCH_7EM__ == 1))
+    return __PKHBT(val, val, 16);
+    #else
+    val &= 0x0000ffff;
+    return val | (val << 16);
+    #endif
+}
+
+static inline uint32_t copy16msb(uint32_t val) {
+    #if (defined(__ARM_ARCH_7EM__) && (__ARM_ARCH_7EM__ == 1))
+    return __PKHTB(val, val, 16);
+    #else
+    val &= 0xffff0000;
+    return val | (val >> 16);
+    #endif
+}
+
 size_t usb_audio_usbmicrophone_background_fill(uint8_t *out, size_t max_bytes) {
     usb_audio_usbmicrophone_obj_t *self = active_microphone;
     if (self == NULL || !self->playing || self->paused || self->sample == MP_OBJ_NULL) {
         return 0;
     }
 
-    // The negotiated USB format is 16-bit signed mono PCM. For this step the
+    // The negotiated USB format is 16-bit signed PCM. For this step the
     // bound sample is assumed to already be in that format (e.g. a 16-bit signed
-    // mono audiocore.RawSample), so its bytes are copied straight through.
+    // audiocore.RawSample), so its bytes are copied straight through.
     size_t filled = 0;
     while (filled < max_bytes) {
         if (self->buffer_length == 0) {
@@ -138,8 +157,20 @@ size_t usb_audio_usbmicrophone_background_fill(uint8_t *out, size_t max_bytes) {
             }
         }
 
-        size_t n = MIN(self->buffer_length, max_bytes - filled);
-        memcpy(out + filled, self->buffer, n);
+        size_t n;
+        if (MP_LIKELY(usb_audio_channel_count == USB_AUDIO_N_CHANNELS)) {
+            n = MIN(self->buffer_length, max_bytes - filled);
+            memcpy(out + filled, self->buffer, n);
+        } else {
+            n = MIN(self->buffer_length << 1, max_bytes - filled);
+            uint32_t *word_buffer = (uint32_t *)self->buffer;
+            uint32_t *word_out = (uint32_t *)(out + filled);
+            for (size_t i = 0; i < n / sizeof(uint32_t); i += 2) {
+                uint32_t v = word_buffer[i >> 1];
+                word_out[i] = copy16lsb(v);
+                word_out[i + 1] = copy16msb(v);
+            }
+        }
         self->buffer += n;
         self->buffer_length -= n;
         filled += n;

shared-module/usb_audio/USBSpeaker.c

@@ -32,12 +32,12 @@ void common_hal_usb_audio_usbspeaker_construct(usb_audio_usbspeaker_obj_t *self)
     // format we present is 16-bit signed LE PCM, which is exactly what the
     // CircuitPython audio pipeline carries, so no conversion is needed.
     self->base.sample_rate = usb_audio_sample_rate;
-    self->base.bits_per_sample = usb_audio_bits_per_sample;
+    self->base.bits_per_sample = USB_AUDIO_BITS_PER_SAMPLE;
     self->base.channel_count = usb_audio_channel_count;
     self->base.samples_signed = true;
     self->base.single_buffer = false;
     self->base.max_buffer_length = USB_AUDIO_SPEAKER_OUTPUT_BUFFER_SIZE;
-
+    
     self->ring_head = 0;
     self->ring_tail = 0;
     self->ring_count = 0;
@@ -193,16 +193,29 @@ audioio_get_buffer_result_t usb_audio_usbspeaker_get_buffer(usb_audio_usbspeaker
 
     uint32_t half = self->base.max_buffer_length / 2;
     uint8_t *out = self->output_buffer + half * self->output_index;
+    int16_t *word_out = (int16_t *)out;
+    int16_t *word_ring = (int16_t *)self->ring;
     self->output_index = 1 - self->output_index;
 
     // Consumer side of the SPSC ring (runs in the output backend's refill ISR).
     // It is never preempted by the producer, so no interrupt guard is required.
     size_t to_copy = MIN(self->ring_count, (size_t)half);
 
     size_t first = MIN(to_copy, USB_AUDIO_SPEAKER_RING_SIZE - self->ring_tail);
-    memcpy(out, &self->ring[self->ring_tail], first);
-    if (to_copy > first) {
-        memcpy(out + first, &self->ring[0], to_copy - first);
+    if (MP_LIKELY(usb_audio_channel_count == USB_AUDIO_N_CHANNELS)) {
+        memcpy(out, &self->ring[self->ring_tail], first);
+        if (to_copy > first) {
+            memcpy(out + first, &self->ring[0], to_copy - first);
+        }
+    } else {
+        for (size_t i = self->ring_tail / USB_AUDIO_N_BYTES_PER_SAMPLE; i < first / USB_AUDIO_N_BYTES_PER_SAMPLE; i += 2) {
+            word_out[i >> 1] = word_ring[i];
+        }
+        if (to_copy > first) {
+            for (size_t i = 0; i < (to_copy - first) / USB_AUDIO_N_BYTES_PER_SAMPLE; i += 2) {
+                word_out[(first / USB_AUDIO_N_BYTES_PER_SAMPLE) + (i >> 1)] = word_ring[i];
+            }
+        }
     }
     self->ring_tail = (self->ring_tail + to_copy) % USB_AUDIO_SPEAKER_RING_SIZE;
     self->ring_count -= to_copy;
@@ -211,17 +224,25 @@ audioio_get_buffer_result_t usb_audio_usbspeaker_get_buffer(usb_audio_usbspeaker
         // Underrun: pad the remainder with silence. Samples are signed, so
         // silence is 0. This is the consume-side of the pacing failure mode
         // tracked in the usb-audio-artifact-pacing memory: we never spin.
-        memset(out + to_copy, 0, half - to_copy);
+        if (MP_LIKELY(usb_audio_channel_count == USB_AUDIO_N_CHANNELS)) {
+            memset(out + to_copy, 0, half - to_copy);
+        } else {
+            memset(out + (to_copy >> 1), 0, (half - to_copy) >> 1);
+        }
     }
 
-    // Mono only for v1, so the single-channel offset is always 0; computed the
-    // same way as audiocore.RawSample so stereo (interleaved ring) can extend it.
+    // Computed the same way as audiocore.RawSample so stereo (interleaved ring)
+    // can extend it.
     if (single_channel_output) {
         out += (channel % self->base.channel_count) * (self->base.bits_per_sample / 8);
     }
 
     *buffer = out;
-    *buffer_length = half;
+    if (MP_LIKELY(usb_audio_channel_count == USB_AUDIO_N_CHANNELS)) {
+        *buffer_length = half;
+    } else {
+        *buffer_length = half >> 1;
+    }
     // A live USB stream is infinite; never report DONE or the backend would stop.
     return GET_BUFFER_MORE_DATA;
 }

shared-module/usb_audio/USBSpeaker.h

@@ -22,7 +22,7 @@
 // comfortably inside the ring.
 #define USB_AUDIO_SPEAKER_FRAMES_PER_BUFFER (128)
 
-// Bytes per audio frame in the negotiated UAC2 format (mono 16-bit for v1).
+// Bytes per audio frame in the negotiated UAC2 format (stereo 16-bit).
 #define USB_AUDIO_SPEAKER_BYTES_PER_FRAME (USB_AUDIO_N_BYTES_PER_SAMPLE * USB_AUDIO_N_CHANNELS)
 
 // Full owned double-buffer: two halves of FRAMES_PER_BUFFER frames each. Matches