Feather M4 (SAMD51) Disable/Re-Enable I2S

Using Arduino Microcontrollers
#1

Hey Guys,

Having a bit of trouble using I2S on a SAMD51 and then disabling I2S, sleeping and then re-enabling and using I2S again.

I’m using a modified version of the WavFilePlayer example from the Adafruit fork of the Audio library (GitHub - adafruit/Audio: Teensy Audio Library). I’ve been struggling a bit trying to figure out how to re-initialize I2S after going into a low-power sleep mode. It would be useful to look at the code I am using to give you guys an idea of what I am talking about. Here is what I am using, basically as I said a modified version of the WavFilePlayer example, with sleep integrated into it:

#include <Audio.h>[color=#2e8b57][/color]
#include <SdFat.h>[color=#2e8b57][/color]
#include <Adafruit_SPIFlash.h>[color=#2e8b57][/color]
#include <play_fs_wav.h>[color=#2e8b57][/color]
#include <Adafruit_SleepyDog.h>[color=#2e8b57][/color]
[color=#2e8b57][/color]
AudioPlayFSWav           playFSWav;[color=#2e8b57][/color]
AudioOutputI2S           audioOutput;[color=#2e8b57][/color]
AudioConnection          patchCord1(playFSWav, 0, audioOutput, 1);[color=#2e8b57][/color]
AudioConnection          patchCord2(playFSWav, 1, audioOutput, 0);[color=#2e8b57][/color]
[color=#2e8b57][/color]
Adafruit_FlashTransport_QSPI flashTransport(PIN_QSPI_SCK, PIN_QSPI_CS, PIN_QSPI_IO0, PIN_QSPI_IO1, PIN_QSPI_IO2, PIN_QSPI_IO3);[color=#2e8b57][/color]
[color=#2e8b57][/color]
Adafruit_SPIFlash flash(&flashTransport);[color=#2e8b57][/color]
FatFileSystem QSPIFS;[color=#2e8b57][/color]
SdFat SD;[color=#2e8b57][/color]
bool QSPIOK = false;[color=#2e8b57][/color]
[color=#2e8b57][/color]
int pin_i2s_power = 6;[color=#2e8b57][/color]
int pin_i2s_din = 11;[color=#2e8b57][/color]
int pin_i2s_lrclk = 10;[color=#2e8b57][/color]
int pin_i2s_tx_d1 = 1;[color=#2e8b57][/color]
[color=#2e8b57][/color]
void setup() {[color=#2e8b57][/color]
  pinMode(6, OUTPUT);[color=#2e8b57][/color]
  digitalWrite(6, HIGH);[color=#2e8b57][/color]
[color=#2e8b57][/color]
  AudioMemory(8);[color=#2e8b57][/color]
[color=#2e8b57][/color]
  QSPIOK = false;[color=#2e8b57][/color]
  if (!flash.begin()) {[color=#2e8b57][/color]
    Serial.println("Error, failed to initialize flash chip!");[color=#2e8b57][/color]
  } else if (!QSPIFS.begin(&flash)) {[color=#2e8b57][/color]
    Serial.println("Failed to mount QSPI filesystem!");[color=#2e8b57][/color]
    Serial.println("Was CircuitPython loaded on the board first to create the filesystem?");[color=#2e8b57][/color]
  } else {[color=#2e8b57][/color]
    Serial.println("QSPI OK!");[color=#2e8b57][/color]
    QSPIOK = true;[color=#2e8b57][/color]
  }[color=#2e8b57][/color]
   playFSWav.changeVolume(1.0);[color=#2e8b57][/color]
}[color=#2e8b57][/color]
[color=#2e8b57][/color]
void playFile(const char *filename)[color=#2e8b57][/color]
{[color=#2e8b57][/color]
  File f = QSPIFS.open(filename);[color=#2e8b57][/color]
 [color=#2e8b57][/color]
  if (!playFSWav.play(f)) {[color=#2e8b57][/color]
    Serial.println("Failed to play");[color=#2e8b57][/color]
    return;[color=#2e8b57][/color]
  }[color=#2e8b57][/color]
  Serial.println("QSPI OK!");[color=#2e8b57][/color]
}[color=#2e8b57][/color]
[color=#2e8b57][/color]
[color=#2e8b57][/color]
void loop() {[color=#2e8b57][/color]
 [color=#2e8b57][/color]
    digitalWrite(6, HIGH);[color=#2e8b57][/color]
[color=#2e8b57][/color]
    playFile("battery.wav");[color=#2e8b57][/color]
    delay(6);[color=#2e8b57][/color]
    while(playFSWav.isPlaying()) delay(1);[color=#2e8b57][/color]
[color=#2e8b57][/color]
    enterLowPowerState();[color=#2e8b57][/color]
    Watchdog.sleep(2000);[color=#2e8b57][/color]
   [color=#2e8b57][/color]
}[color=#2e8b57][/color]
[color=#2e8b57][/color]
void enterLowPowerState() {[color=#2e8b57][/color]
[color=#2e8b57][/color]
  if (!playFSWav.isPlaying()) {[color=#2e8b57][/color]
    digitalWrite(pin_i2s_power, LOW);[color=#2e8b57][/color]
    I2S->CTRLA.bit.ENABLE=0;//THIS ACHIEVES HUGE POWER SAVINGS, BUT I DON'T KNOW HOW TO TURN IT BACK ON[color=#2e8b57][/color]
  }[color=#2e8b57][/color]
[color=#2e8b57][/color]
}

You can see where I turn off “I2S->CTRLA.bit.ENABLE=0;” and it achieves amazing power savings, but I can’t figure out how to reinitialize and make it work. How do I get out of sleep and play another WAV file? I thought it would be something simple like I2S->CTRLA.bit.ENABLE=1; … any ideas on why that wouldn’t work or other solutions? Could one simply shut off the clocks to I2S? I couldn’t figure out how to do that. Thanks guys!

#2

Hi Casey10110,

Although it might not be the problem, it is however necessary to wait for the I2S's CTRLA register to synchronize, when setting or clearing the ENABLE bit:

I2S->CTRLA.bit.ENABLE = 0;  // Disable the I2S peripheral
while (I2S->SYNCBUSY.bit.ENABLE);  // Wait for synchronization

This will ensure that the I2S module has indeed been disabled, before putting the microcontroller to sleep.

#3

For sure, thanks Martin. Unfortunately that isn't the issue. I think there must be some more things that get "uninitialized" when disabling the I2S and I'm trying to figure out how to reconfigure ...

#4