Classify ARM Chromebooks as high latency audio.

ppapi/shared_impl/ppb_audio_config_shared.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "build/build_config.h"
 #include "ppapi/shared_impl/ppb_audio_config_shared.h"
 #include "ppapi/thunk/enter.h"
 #include "ppapi/thunk/ppb_instance_api.h"
 
 namespace ppapi {
 
 // Rounds up requested_size to the nearest multiple of minimum_size.
 static uint32_t CalculateMultipleOfSampleFrameCount(uint32_t minimum_size,
                                                     uint32_t requested_size) {
   const uint32_t multiple = (requested_size + minimum_size - 1) / minimum_size;
@@ skipping 59 matching lines @@
   // output stream on the browser side, so we can use whatever sample count the
   // client wants.
   if (!hardware_sample_frame_count || !hardware_sample_rate)
     return sample_frame_count;
 
   // Note: All the values below were determined through experimentation to
   // minimize jitter and back-to-back callbacks from the browser.  Please take
   // care when modifying these values as they impact a large number of users.
   // TODO(dalecurtis): Land jitter test and add documentation for updating this.
 
+  // Should track the value reported by XP and ALSA backends.
+  const uint32_t kHighLatencySampleFrameCount = 2048;
+
+#if defined(OS_CHROMEOS) && defined(ARCH_CPU_ARM_FAMILY)
+  // TODO(ihf): Remove this once ARM Chromebooks support low latency audio. For
+  // now we classify them as high latency. See crbug.com/289770.

[dmichael (off chromium), 2013/09/13 20:44:46]

This doesn't seem like the right place to fix this. Pepper shouldn't need to
know much about specific hardware; that should usually be shared. What about
AudioHardwareConfig?:
https://code.google.com/p/chromium/codesearch#chromium/src/media/base/audio_h...

+  return CalculateMultipleOfSampleFrameCount(
+      sample_frame_count, kHighLatencySampleFrameCount);

[dmichael (off chromium), 2013/09/13 21:15:56]

should we copy the high latency section below and use:
std::max(kHighLatencySampleFrameCount, hardware_sample_frame_count);
?

Or add another way in to that "if" condition, so we don't need this separate
call? E.g.:
#if defined(OS_CHROMEOS) && defined(ARCH_CPU_ARM_FAMILY)
const bool kHighLatencyDevice = true;
#else
const bool kHighLatencyDevice = true;
#endif

and edit 106 to say
if (kHighLatencyDevice ||
    //... etc ...

Also, it would be nice to comment on why we do this platform checking here
instead of at a lower level.

[ilja, 2013/09/14 01:44:39]

I followed the second approach and left a comment.

+#endif  // defined(OS_CHROMEOS) && defined(ARCH_CPU_ARM_FAMILY)
+
   // If client is using same sample rate as audio hardware, then recommend a
   // multiple of the audio hardware's sample frame count.
   if (hardware_sample_rate == sample_rate) {
     return CalculateMultipleOfSampleFrameCount(
         hardware_sample_frame_count, sample_frame_count);
   }
 
-  // Should track the value reported by XP and ALSA backends.
-  const uint32_t kHighLatencySampleFrameCount = 2048;
-
   // If the hardware requires a high latency buffer or we're at a low sample
   // rate w/ a buffer that's larger than 10ms, choose the nearest multiple of
   // the high latency sample frame count.  An example of too low and too large
   // is 16kHz and a sample frame count greater than 160 frames.
   if (hardware_sample_frame_count >= kHighLatencySampleFrameCount ||
       (hardware_sample_rate < 44100 &&
        hardware_sample_frame_count > hardware_sample_rate / 100u)) {
     return CalculateMultipleOfSampleFrameCount(
         sample_frame_count,
         std::max(kHighLatencySampleFrameCount, hardware_sample_frame_count));
@@ skipping 57 matching lines @@
   if (sample_frame_count > PP_AUDIOMAXSAMPLEFRAMECOUNT ||
       sample_frame_count < PP_AUDIOMINSAMPLEFRAMECOUNT)
     return false;
 
   sample_rate_ = sample_rate;
   sample_frame_count_ = sample_frame_count;
   return true;
 }
 
 }  // namespace ppapi