pcm_export: support DSD to DSD-over-USB conversion

src/output/alsa_output_plugin.c

@@ -633,8 +633,9 @@ alsa_setup_or_dsd(struct alsa_data *ad, struct audio_format *audio_format,
 	if (!success)
 		return false;
 
-	pcm_export_open(&ad->export, audio_format->format,
-			packed, reverse_endian);
+	pcm_export_open(&ad->export,
+			audio_format->format, audio_format->channels,
+			false, packed, reverse_endian);
 	return true;
 }
 
@@ -777,7 +778,8 @@ alsa_play(struct audio_output *ao, const void *chunk, size_t size,
 		if (ret > 0) {
 			ad->period_position = (ad->period_position + ret)
 				% ad->period_frames;
-			return ret * ad->in_frame_size;
+			return pcm_export_source_size(&ad->export,
+						      ret * ad->in_frame_size);
 		}
 
 		if (ret < 0 && ret != -EAGAIN && ret != -EINTR &&

src/output/oss_output_plugin.c

@@ -540,7 +540,7 @@ oss_probe_sample_format(int fd, enum sample_format sample_format,
 	*oss_format_r = oss_format;
 
 #ifdef AFMT_S24_PACKED
-	pcm_export_open(export, sample_format,
+	pcm_export_open(export, sample_format, 0, false,
 			oss_format == AFMT_S24_PACKED,
 			oss_format == AFMT_S24_PACKED &&
 			G_BYTE_ORDER != G_LITTLE_ENDIAN);
@@ -755,8 +755,12 @@ oss_output_play(struct audio_output *ao, const void *chunk, size_t size,
 
 	while (true) {
 		ret = write(od->fd, chunk, size);
-		if (ret > 0)
-			return (size_t)ret;
+		if (ret > 0) {
+#ifdef AFMT_S24_PACKED
+			ret = pcm_export_source_size(&od->export, ret);
+#endif
+			return ret;
+		}
 
 		if (ret < 0 && errno != EINTR) {
 			g_set_error(error, oss_output_quark(), errno,

src/pcm_export.c

@@ -19,6 +19,7 @@
 
 #include "config.h"
 #include "pcm_export.h"
+#include "pcm_dsd_usb.h"
 #include "pcm_pack.h"
 #include "util/byte_reverse.h"
 
@@ -27,19 +28,31 @@ pcm_export_init(struct pcm_export_state *state)
 {
 	pcm_buffer_init(&state->reverse_buffer);
 	pcm_buffer_init(&state->pack_buffer);
+	pcm_buffer_init(&state->dsd_buffer);
 }
 
 void pcm_export_deinit(struct pcm_export_state *state)
 {
 	pcm_buffer_deinit(&state->reverse_buffer);
 	pcm_buffer_deinit(&state->pack_buffer);
+	pcm_buffer_deinit(&state->dsd_buffer);
 }
 
 void
 pcm_export_open(struct pcm_export_state *state,
-		enum sample_format sample_format,
-		bool pack, bool reverse_endian)
+		enum sample_format sample_format, unsigned channels,
+		bool dsd_usb, bool pack, bool reverse_endian)
 {
+	assert(audio_valid_sample_format(sample_format));
+	assert(!dsd_usb || audio_valid_channel_count(channels));
+
+	state->channels = channels;
+	state->dsd_usb = dsd_usb && sample_format == SAMPLE_FORMAT_DSD;
+	if (state->dsd_usb)
+		/* after the conversion to DSD-over-USB, the DSD
+		   samples are stuffed inside fake 24 bit samples */
+		sample_format = SAMPLE_FORMAT_S24_P32;
+
 	state->pack24 = pack && (sample_format == SAMPLE_FORMAT_S24_P32 || sample_format == SAMPLE_FORMAT_DSD_OVER_USB);
 
 	state->reverse_endian = 0;
@@ -58,6 +71,10 @@ const void *
 pcm_export(struct pcm_export_state *state, const void *data, size_t size,
 	   size_t *dest_size_r)
 {
+	if (state->dsd_usb)
+		data = pcm_dsd_to_usb(&state->dsd_buffer, state->channels,
+				      data, size, &size);
+
 	if (state->pack24) {
 		assert(size % 4 == 0);
 
@@ -90,3 +107,13 @@ pcm_export(struct pcm_export_state *state, const void *data, size_t size,
 	*dest_size_r = size;
 	return data;
 }
+
+size_t
+pcm_export_source_size(const struct pcm_export_state *state, size_t size)
+{
+	if (state->dsd_usb)
+		/* DSD over USB doubles the transport size */
+		size /= 2;
+
+	return size;
+}

src/pcm_export.h

@@ -35,6 +35,14 @@ struct audio_format;
  */
 struct pcm_export_state {
 	/**
+	 * The buffer is used to convert DSD samples to the
+	 * DSD-over-USB format.
+	 *
+	 * @see #dsd_usb
+	 */
+	struct pcm_buffer dsd_buffer;
+
+	/**
 	 * The buffer is used to pack samples, removing padding.
 	 *
 	 * @see #pack24
@@ -49,6 +57,18 @@ struct pcm_export_state {
 	struct pcm_buffer reverse_buffer;
 
 	/**
+	 * The number of channels.
+	 */
+	uint8_t channels;
+
+	/**
+	 * Convert DSD to DSD-over-USB?  Input format must be
+	 * SAMPLE_FORMAT_DSD and output format must be
+	 * SAMPLE_FORMAT_S24_P32.
+	 */
+	bool dsd_usb;
+
+	/**
 	 * Pack 24 bit samples?
 	 */
 	bool pack24;
@@ -80,11 +100,13 @@ pcm_export_deinit(struct pcm_export_state *state);
  * times to reuse the object, until pcm_export_deinit() is called.
  *
  * This function cannot fail.
+ *
+ * @param channels the number of channels; ignored unless dsd_usb is set
  */
 void
 pcm_export_open(struct pcm_export_state *state,
-		enum sample_format sample_format,
-		bool pack, bool reverse_endian);
+		enum sample_format sample_format, unsigned channels,
+		bool dsd_usb, bool pack, bool reverse_endian);
 
 /**
  * Export a PCM buffer.
@@ -99,4 +121,13 @@ const void *
 pcm_export(struct pcm_export_state *state, const void *src, size_t src_size,
 	   size_t *dest_size_r);
 
+/**
+ * Converts the number of consumed bytes from the pcm_export()
+ * destination buffer to the according number of bytes from the
+ * pcm_export() source buffer.
+ */
+G_GNUC_PURE
+size_t
+pcm_export_source_size(const struct pcm_export_state *state, size_t dest_size);
+
 #endif