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output/alsa: support 32 bit DSD-over-USB

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This commit is contained in:
Max Kellermann 2012-03-27 01:05:33 +02:00
parent ddd4f675a2
commit 2803ec2e96
1 changed files with 15 additions and 4 deletions
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19
src/output/alsa_output_plugin.c
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@ -588,7 +588,8 @@ error:
static bool
alsa_setup_dsd(struct alsa_data *ad, struct audio_format *audio_format,
bool *packed_r, bool *reverse_endian_r, GError **error_r)
bool *shift8_r, bool *packed_r, bool *reverse_endian_r,
GError **error_r)
{
assert(ad->dsd_usb);
assert(audio_format->format == SAMPLE_FORMAT_DSD);
@ -604,6 +605,15 @@ alsa_setup_dsd(struct alsa_data *ad, struct audio_format *audio_format,
if (!alsa_setup(ad, &usb_format, packed_r, reverse_endian_r, error_r))
return false;
/* if the device allows only 32 bit, shift all DSD-over-USB
samples left by 8 bit and leave the lower 8 bit cleared;
the DSD-over-USB documentation does not specify whether
this is legal, but there is anecdotical evidence that this
is possible (and the only option for some devices) */
*shift8_r = usb_format.format == SAMPLE_FORMAT_S32;
if (usb_format.format == SAMPLE_FORMAT_S32)
usb_format.format = SAMPLE_FORMAT_S24_P32;
if (!audio_format_equals(&usb_format, &check)) {
/* no bit-perfect playback, which is required
for DSD over USB */
@ -620,12 +630,13 @@ static bool
alsa_setup_or_dsd(struct alsa_data *ad, struct audio_format *audio_format,
GError **error_r)
{
bool packed, reverse_endian;
bool shift8 = false, packed, reverse_endian;
const bool dsd_usb = ad->dsd_usb &&
audio_format->format == SAMPLE_FORMAT_DSD;
const bool success = dsd_usb
? alsa_setup_dsd(ad, audio_format, &packed, &reverse_endian,
? alsa_setup_dsd(ad, audio_format,
&shift8, &packed, &reverse_endian,
error_r)
: alsa_setup(ad, audio_format, &packed, &reverse_endian,
error_r);
@ -634,7 +645,7 @@ alsa_setup_or_dsd(struct alsa_data *ad, struct audio_format *audio_format,
pcm_export_open(&ad->export,
audio_format->format, audio_format->channels,
dsd_usb, false, packed, reverse_endian);
dsd_usb, shift8, packed, reverse_endian);
return true;
}