USB storage initialization fails if performed inside connection callback

[haveyouseenf]

I wrote a simple sketch for the Opta that creates a new file in the root folder of a connected USB device and then writes inside it.

I planned to use the connection callback to immediately initialize the USB storage, but unfortunately it did not work. In fact the following sketch cannot create a new file:

Click to expand

#include <Arduino_UnifiedStorage.h>

USBStorage usbStorage;
volatile bool usbAvailable = false;

void setup()
{
    // Disable debugging of storage operations.
    Arduino_UnifiedStorage::debuggingModeEnabled = false;

    // Init USBStorage object.
    usbStorage = USBStorage();

    // Register connect callback.
    usbStorage.onConnect(connectionCallback);
    usbStorage.onDisconnect(disconnectionCallback);
}

void loop()
{
    while (!usbAvailable)
    {
        digitalWrite(LED_USER, HIGH);
        delay(200);
        digitalWrite(LED_USER, LOW);
        delay(200);
    }
    digitalWrite(LED_USER, LOW);

    Folder root = usbStorage.getRootFolder();
    UFile outFile = root.createFile("test.txt", FileMode::APPEND);
    outFile.write("Hello, World!");
    outFile.close();
    usbStorage.unmount();

    digitalWrite(LED_USER, HIGH);
    while (1)
    {
    }
}

void connectionCallback()
{
    usbAvailable = true;
    usbStorage.removeOnConnectCallback();

    // This does not work!
    if (!usbStorage.isMounted())
    {
        usbStorage.begin();
    }
}

void disconnectionCallback()
{
    usbAvailable = false;
    usbStorage.onConnect(connectionCallback);
}

Furthemore, I suspect the storage might not be initialized at all when using the above code, as a simple call to root.exists() in the loop would halt the execution causing a board reset.

If I instead move the storage initialization code in the loop() function, the sketch works as expected. I will attach the functioning sketch below for completeness:

Click to expand

#include <Arduino_UnifiedStorage.h>

USBStorage usbStorage;
volatile bool usbAvailable = false;

void setup()
{
    // Disable debugging of storage operations.
    Arduino_UnifiedStorage::debuggingModeEnabled = false;

    // Init USBStorage object.
    usbStorage = USBStorage();

    // Register connect callback.
    usbStorage.onConnect(connectionCallback);
    usbStorage.onDisconnect(disconnectionCallback);
}

void loop()
{
    while (!usbAvailable)
    {
        digitalWrite(LED_USER, HIGH);
        delay(200);
        digitalWrite(LED_USER, LOW);
        delay(200);
    }
    digitalWrite(LED_USER, LOW);

    // This works!
    if (!usbStorage.isMounted())
    {
        usbStorage.begin();
    }

    Folder root = usbStorage.getRootFolder();
    UFile outFile = root.createFile("test.txt", FileMode::APPEND);
    outFile.write("Hello, World!");
    outFile.close();
    usbStorage.unmount();

    digitalWrite(LED_USER, HIGH);
    while (1)
    {
    }
}

void connectionCallback()
{
    usbAvailable = true;
    usbStorage.removeOnConnectCallback();
}

void disconnectionCallback()
{
    usbAvailable = false;
    usbStorage.onConnect(connectionCallback);
}

I did not find any mention of this behavior in the docs. If I can provide further details or assistance ping me!