Adafruit Joy Featherwing not responding to interrupts when using Seesaw library about adafruit_seesaw

[ladyada]

ooooh thats interesting and not something we knew about but yeah irq's are not as simple as we'd like and arduino uses A LOT of them behind the scenes.
can you submit a PR with this example sketch? call it like "seesaw_ESP32_IRQ" ?

[theficus]

Yes, absolutely. Hopefully it can save else from falling into this same trap in the future. I’ll try to get a PR done this weekend.

[theficus]

I did some extensive debugging into this issue this evening and I believe I understand what's going on. It appears that what is happening is when the ISR is calling into the ESP TwoWire library to read data from the I2C bus, it will ultimately fail with I2C_ERROR_BUSY and this is unrecoverable.

Digging further into this, it appears that there are some known limitations on the ESP platform specific to doing I2C operations from within an ISR due to how its FreeRTOS handles task switching. The recommendation for this seems to be to use a ESP task queue to do the work, and have the ISR simply signal the queue to do something. I played around with this some and actually made some pretty good progress.

Here's some prototype sample code (incomplete -- based on the original sample):

QueueHandle_t joyQueue;

void onButtonPress()
{
    int i = 0;
    xQueueSend(joyQueue, &i, portMAX_DELAY);
}

void joyTaskConsumer(void* p)
{
    Serial.println("In queue!");
    int element;
    size_t i = 0;
    while(true)
    {
        Serial.printf("q=%zu\n", i);
        xQueueReceive(joyQueue, &element, portMAX_DELAY);
        uint32_t v = 0;
        v = ss.digitalReadBulk(s_button_mask);
        Serial.println(v, BIN);
        i++;
    }
    vTaskDelete(NULL);
}

void setup()
{
    Serial.begin(115200);
    joyQueue = xQueueCreate(10, sizeof(int));
    ss.begin(0x49);
    ss.pinModeBulk(s_button_mask, INPUT_PULLUP);
    ss.setGPIOInterrupts(s_button_mask, true);
    pinMode(JOY_IRQ_PIN, INPUT);
    
    xTaskCreate(
        joyTaskConsumer,
        "JoyTaskConsumer",
        10000,
        NULL,
        1,
        NULL);

    attachInterrupt(JOY_IRQ_PIN, onButtonPress, FALLING);
}

This actually seems to work reasonably well -- I am seeing events fire pretty much immediately when the button is depressed and released and on every subsequent button press, and the queue task simply cedes to any other work on the CPU until something gets queued which is basically what I want. In my testing I am running into a new issue where pressing too many buttons at once or too quickly can eventually cause the ESP32 to crash which I'm still troubleshooting (I think this is due to a race with the Serial.println statement), but in all this is working a million times better than before!

It's possible I could also use a semaphore or some other similar approach to do this if I wanted to and I'll do some more experimentation. It seems like the key thing here is to keep the actual work of communicating with the I2C bus out of the ISR.

So in conclusion this seems more like an issue specific to the interrupt use case with the ESP platform rather than a simple bug or PEBKAC problem. This would probably be something useful to call out in the docs or samples as this is something that can come as quite a shock to someone who's trying to use interrupts but is new to the ESP platform.

Further reading:

• https://www.eevblog.com/forum/embedded-computing/esp32-not-possible-to-use-i2c-functions-in-an-isr/

[ladyada]

awesome thankx :)

[theficus]

I figured out a fix to the crashes in my sample and also added support for reading the analog stick in a separate task. This allows the ESP32 to handle all controller inputs without blocking other work. I’ll update the sample with this when I get a chance and will close this Issue out when that’s done.

[theficus]

Going to close this after checking in some sample code demonstrating an approach for getting this to work on an ESP32.

Hopefully this saves somebody else some time and headaches. :)