AudioPlayQueue stalls internally

[h4yn0nnym0u5e]

Description

AudioPlayQueue::getBuffer() and ::playBuffer() can stall internally, dramatically impacting user code throughput. Teensyduino 1.56 beta 3 has a new ::play() function, which uses both these functions, and thus suffers the same issue.

This behaviour is undocumented, and appears to be hard (impossible?) to work around in the user's application.

Steps To Reproduce Problem

Run the example sketch, and note that loop() iterates very slowly.

Hardware & Software

Board: any
Shields / modules used: any
Arduino IDE version: any
Teensyduino version: 1.56 beta 3
Operating system & version: any
Any other software or hardware?: no

Arduino Sketch

#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>

// GUItool: begin automatically generated code
AudioPlayQueue           queue1;         //xy=917,329
AudioOutputI2S           i2s2;           //xy=1121,330
AudioConnection          patchCord1(queue1, 0, i2s2, 0);
AudioConnection          patchCord2(queue1, 0, i2s2, 1);
AudioControlSGTL5000     sgtl5000_1;     //xy=1131,379
// GUItool: end automatically generated code


uint32_t next;
void setup() {
  pinMode(13,OUTPUT);
  
  Serial.begin(115200);
  while (!Serial)
    ;

  if (CrashReport) 
  {
    Serial.println(CrashReport);
    CrashReport.clear();
  }

  AudioMemory(10);
  
  sgtl5000_1.enable();
  sgtl5000_1.volume(0.5);

  next = millis();
}

int loops;
int nulls;
float phas;
void loop() {
  int16_t* buf = queue1.getBuffer();
  
  if (NULL == buf)
    nulls++;
  else
  {
    for (int i=0;i<AUDIO_BLOCK_SAMPLES;i++)
    {
      buf[i] = (int16_t) (sin(phas)*8000.);
      phas += 220./AUDIO_SAMPLE_RATE_EXACT*TWO_PI;
      if (phas > TWO_PI)
        phas -= TWO_PI;
    }
    queue1.playBuffer();
  }

  loops++;
  if (millis() > next)
  {
    next += 100;
    Serial.printf("millis = %d, loops = %d, nulls = %d\n",millis(),loops,nulls);
  }
}

Errors or Incorrect Output

Program output from running on Teensy 4.1. Note that we achieve about 345 iterations of loop() per second, because NULL is never returned from getBuffer()

millis = 736, loops = 2, nulls = 0
millis = 837, loops = 44, nulls = 0
millis = 936, loops = 78, nulls = 0
millis = 1037, loops = 113, nulls = 0
millis = 1136, loops = 147, nulls = 0
millis = 1237, loops = 182, nulls = 0
millis = 1336, loops = 216, nulls = 0
millis = 1438, loops = 251, nulls = 0
millis = 1536, loops = 285, nulls = 0
millis = 1638, loops = 320, nulls = 0
millis = 1737, loops = 354, nulls = 0
millis = 1838, loops = 389, nulls = 0
millis = 1937, loops = 423, nulls = 0
millis = 2036, loops = 457, nulls = 0
millis = 2137, loops = 492, nulls = 0
millis = 2236, loops = 526, nulls = 0
millis = 2338, loops = 561, nulls = 0
millis = 2436, loops = 595, nulls = 0
millis = 2538, loops = 630, nulls = 0
millis = 2636, loops = 664, nulls = 0
millis = 2738, loops = 699, nulls = 0
millis = 2837, loops = 733, nulls = 0

[h4yn0nnym0u5e]

Fixed by PR #417, which has been merged. But see PR #459 - demo is broken.