commit 0caeee8ac429dd8098e97b2cd8ad3751031a5b67
author Andy Hung <hunga@google.com> Fri Jun 24 19:41:06 2016 -0700
committer Andy Hung <hunga@google.com> Wed Jul 13 11:19:40 2016 -0700
tree 31c63f48b707231fae726b330b327dd4efc241ca
parent 61187f61ef67e19d20b09994ee31635cee862bb4

Improve stub hal read and write timing

Now considers time to mix or record.

Bug: 29634175
Change-Id: Ifb2a2e11cb75ca9e83aadbc95943a618b0707f3f

modules/audio/audio_hw.c

diff --git a/modules/audio/audio_hw.c b/modules/audio/audio_hw.c
index a1a322f..68b0d3a 100644
--- a/modules/audio/audio_hw.c
+++ b/modules/audio/audio_hw.c
@@ -35,10 +35,12 @@
 
 struct stub_stream_out {
     struct audio_stream_out stream;
+    int64_t last_write_time_us;
 };
 
 struct stub_stream_in {
     struct audio_stream_in stream;
+    int64_t last_read_time_us;
 };
 
 static uint32_t out_get_sample_rate(const struct audio_stream *stream)
@@ -79,7 +81,7 @@
 static int out_standby(struct audio_stream *stream)
 {
     ALOGV("out_standby");
-
+    // out->last_write_time_us = 0; unnecessary as a stale write time has same effect
     return 0;
 }
 
@@ -118,9 +120,31 @@
                          size_t bytes)
 {
     ALOGV("out_write: bytes: %d", bytes);
+
     /* XXX: fake timing for audio output */
-    usleep((int64_t)bytes * 1000000 / audio_stream_out_frame_size(stream) /
-           out_get_sample_rate(&stream->common));
+    struct stub_stream_out *out = (struct stub_stream_out *)stream;
+    struct timespec t = { .tv_sec = 0, .tv_nsec = 0 };
+    clock_gettime(CLOCK_MONOTONIC, &t);
+    const int64_t now = (t.tv_sec * 1000000000LL + t.tv_nsec) / 1000;
+    const int64_t elapsed_time_since_last_write = now - out->last_write_time_us;
+    int64_t sleep_time = bytes * 1000000LL / audio_stream_out_frame_size(stream) /
+               out_get_sample_rate(&stream->common) - elapsed_time_since_last_write;
+    if (sleep_time > 0) {
+        usleep(sleep_time);
+    } else {
+        // we don't sleep when we exit standby (this is typical for a real alsa buffer).
+        sleep_time = 0;
+    }
+    out->last_write_time_us = now + sleep_time;
+    // last_write_time_us is an approximation of when the (simulated) alsa
+    // buffer is believed completely full. The usleep above waits for more space
+    // in the buffer, but by the end of the sleep the buffer is considered
+    // topped-off.
+    //
+    // On the subsequent out_write(), we measure the elapsed time spent in
+    // the mixer. This is subtracted from the sleep estimate based on frames,
+    // thereby accounting for drain in the alsa buffer during mixing.
+    // This is a crude approximation; we don't handle underruns precisely.
     return bytes;
 }
 
@@ -189,6 +213,8 @@
 
 static int in_standby(struct audio_stream *stream)
 {
+    struct stub_stream_in *in = (struct stub_stream_in *)stream;
+    in->last_read_time_us = 0;
     return 0;
 }
 
@@ -217,9 +243,31 @@
                        size_t bytes)
 {
     ALOGV("in_read: bytes %d", bytes);
+
     /* XXX: fake timing for audio input */
-    usleep((int64_t)bytes * 1000000 / audio_stream_in_frame_size(stream) /
-           in_get_sample_rate(&stream->common));
+    struct stub_stream_in *in = (struct stub_stream_in *)stream;
+    struct timespec t = { .tv_sec = 0, .tv_nsec = 0 };
+    clock_gettime(CLOCK_MONOTONIC, &t);
+    const int64_t now = (t.tv_sec * 1000000000LL + t.tv_nsec) / 1000;
+
+    // we do a full sleep when exiting standby.
+    const bool standby = in->last_read_time_us == 0;
+    const int64_t elapsed_time_since_last_read = standby ?
+            0 : now - in->last_read_time_us;
+    int64_t sleep_time = bytes * 1000000LL / audio_stream_in_frame_size(stream) /
+            in_get_sample_rate(&stream->common) - elapsed_time_since_last_read;
+    if (sleep_time > 0) {
+        usleep(sleep_time);
+    } else {
+        sleep_time = 0;
+    }
+    in->last_read_time_us = now + sleep_time;
+    // last_read_time_us is an approximation of when the (simulated) alsa
+    // buffer is drained by the read, and is empty.
+    //
+    // On the subsequent in_read(), we measure the elapsed time spent in
+    // the recording thread. This is subtracted from the sleep estimate based on frames,
+    // thereby accounting for fill in the alsa buffer during the interim.
     memset(buffer, 0, bytes);
     return bytes;
 }