mirror of https://github.com/hak5/openwrt.git
91 lines
3.5 KiB
Diff
91 lines
3.5 KiB
Diff
From 7756cf7615123045c60b9f9e311d2491a5e23424 Mon Sep 17 00:00:00 2001
|
|
From: wm4 <wm4@nowhere>
|
|
Date: Wed, 13 Jan 2016 19:44:47 +0100
|
|
Subject: [PATCH] bcm2835: interpolate audio delay
|
|
|
|
It appears the GPU only sends us a message all 10ms to update
|
|
the playback progress. Other than this, the playback position
|
|
(what SNDRV_PCM_IOCTL_DELAY will return) is not updated at all.
|
|
Userspace will see jitter up to 10ms in the audio position.
|
|
|
|
Make this a bit nicer for userspace by interpolating the
|
|
position using the CPU clock.
|
|
|
|
I'm not sure if setting snd_pcm_runtime.delay is the right
|
|
approach for this. Or if there is maybe an already existing
|
|
mechanism for position interpolation in the ALSA core.
|
|
|
|
I only set SNDRV_PCM_INFO_BATCH because this appears to remove
|
|
at least one situation snd_pcm_runtime.delay is used, so I have
|
|
to worry less in which place I have to update this field, or
|
|
how it interacts with the rest of ALSA.
|
|
|
|
In the future, it might be nice to use VC_AUDIO_MSG_TYPE_LATENCY.
|
|
One problem is that it requires sending a videocore message, and
|
|
waiting for a reply, which could make the implementation much
|
|
harder due to locking and synchronization requirements.
|
|
---
|
|
sound/arm/bcm2835-pcm.c | 12 +++++++++++-
|
|
sound/arm/bcm2835.h | 1 +
|
|
2 files changed, 12 insertions(+), 1 deletion(-)
|
|
|
|
--- a/sound/arm/bcm2835-pcm.c
|
|
+++ b/sound/arm/bcm2835-pcm.c
|
|
@@ -25,7 +25,7 @@
|
|
/* hardware definition */
|
|
static struct snd_pcm_hardware snd_bcm2835_playback_hw = {
|
|
.info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER |
|
|
- SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID),
|
|
+ SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID | SNDRV_PCM_INFO_BATCH),
|
|
.formats = SNDRV_PCM_FMTBIT_U8 | SNDRV_PCM_FMTBIT_S16_LE,
|
|
.rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_8000_48000,
|
|
.rate_min = 8000,
|
|
@@ -99,6 +99,8 @@ static irqreturn_t bcm2835_playback_fifo
|
|
alsa_stream->pos %= alsa_stream->buffer_size;
|
|
}
|
|
|
|
+ alsa_stream->interpolate_start = ktime_get_ns();
|
|
+
|
|
if (alsa_stream->substream) {
|
|
if (new_period)
|
|
snd_pcm_period_elapsed(alsa_stream->substream);
|
|
@@ -399,6 +401,7 @@ static int snd_bcm2835_pcm_prepare(struc
|
|
alsa_stream->buffer_size = snd_pcm_lib_buffer_bytes(substream);
|
|
alsa_stream->period_size = snd_pcm_lib_period_bytes(substream);
|
|
alsa_stream->pos = 0;
|
|
+ alsa_stream->interpolate_start = ktime_get_ns();
|
|
|
|
audio_debug("buffer_size=%d, period_size=%d pos=%d frame_bits=%d\n",
|
|
alsa_stream->buffer_size, alsa_stream->period_size,
|
|
@@ -495,6 +498,7 @@ snd_bcm2835_pcm_pointer(struct snd_pcm_s
|
|
{
|
|
struct snd_pcm_runtime *runtime = substream->runtime;
|
|
bcm2835_alsa_stream_t *alsa_stream = runtime->private_data;
|
|
+ u64 now = ktime_get_ns();
|
|
|
|
audio_info(" .. IN\n");
|
|
|
|
@@ -503,6 +507,12 @@ snd_bcm2835_pcm_pointer(struct snd_pcm_s
|
|
frames_to_bytes(runtime, runtime->control->appl_ptr),
|
|
alsa_stream->pos);
|
|
|
|
+ /* Give userspace better delay reporting by interpolating between GPU
|
|
+ * notifications, assuming audio speed is close enough to the clock
|
|
+ * used for ktime */
|
|
+ if (alsa_stream->interpolate_start && alsa_stream->interpolate_start < now)
|
|
+ runtime->delay = -(int)div_u64((now - alsa_stream->interpolate_start) * runtime->rate, 1000000000);
|
|
+
|
|
audio_info(" .. OUT\n");
|
|
return snd_pcm_indirect_playback_pointer(substream,
|
|
&alsa_stream->pcm_indirect,
|
|
--- a/sound/arm/bcm2835.h
|
|
+++ b/sound/arm/bcm2835.h
|
|
@@ -137,6 +137,7 @@ typedef struct bcm2835_alsa_stream {
|
|
unsigned int pos;
|
|
unsigned int buffer_size;
|
|
unsigned int period_size;
|
|
+ u64 interpolate_start;
|
|
|
|
uint32_t enable_fifo_irq;
|
|
irq_handler_t fifo_irq_handler;
|