A StreamRecording with low splitter sampling rate fails to stop recording

[microbit-carlos]

With this example code, setting the recording rate to 320 samples per second works, but setting it to 319 hangs when recording and never "stops".

#include "MicroBit.h"
#include "StreamRecording.h"

MicroBit uBit;

const int SAMPLE_RATE = 319;
const int BUFFER_LEN = SAMPLE_RATE * 5;

int main() {
    uBit.init();

    SplitterChannel *splitterChannel = uBit.audio.splitter->createChannel();
    splitterChannel->requestSampleRate( SAMPLE_RATE );
    StreamRecording *recording = new StreamRecording(*splitterChannel, BUFFER_LEN);
    // Setting the mixer channel to a different sampling rate doesn't make a difference
    MixerChannel *recordingChannel = uBit.audio.mixer.addChannel(*recording, SAMPLE_RATE);
    recordingChannel->setVolume(75.0);
    MicroBitAudio::requestActivation();

    while (true) {
        if (uBit.buttonA.isPressed()) {
            recording->erase();
            recording->recordAsync();
            while (recording->isRecording()) {
                uBit.display.print("R");
                uBit.sleep(5);
            }
            uBit.display.clear();
        } else if (uBit.buttonB.isPressed()) {
            recording->playAsync();
            while (recording->isPlaying()) {
                uBit.display.print("P");
                uBit.sleep(20);
            }
            uBit.display.clear();
        }
        uBit.sleep(200);
    }
}

• 319.hex.zip
• 320.hex.zip

To replicate:

• Compile this example or download 319.hex & flash it to the micro:bit
• Press button A to start recording
  • Recording should only last 5 seconds
  • The letter R should show on the display for as long as the device is recording
• No matter how long you wait, the recording never stop
  • There isn't a 020 panic (memory error) thrown either, so if it is indeed recording it must be doing it within the allocated buffer

[martinwork]

Single byte buffers are quietly rejected, though the format has one byte per sample
https://github.com/lancaster-university/codal-core/blob/df05db9e15499bd8906618192a4d482e3836c62f/source/streams/StreamRecording.cpp#L96

data == ManagedBuffer() doesn't seem to add anything.

To reject buffers without a whole sample, the test could be
if( data.length() < DATASTREAM_FORMAT_BYTES_PER_SAMPLE( this->upStream.getFormat()) {

With this, the sample rate borderline for "records forever" moves to 142/143, as in #428

With low sample rates, I think StreamRecording will build a list of tiny buffers, with a 12+ byte overhead for each node
https://github.com/lancaster-university/codal-core/blob/df05db9e15499bd8906618192a4d482e3836c62f/inc/streams/StreamRecording.h#L19