ESP32 Forum

Posted: **Tue Sep 18, 2018 1:56 pm**

Hi all -

I'm trying to get the ESP32 to read input from a UART. I began with the uart_events example from the IDF.

When I send a message to the ESP32, it reads about 65 bytes (the exact number varies a bit) and the read returns. I then get subsequent read events of 5 to 9 bytes each, but the data is not what I sent (appears to be garbage). I'm also getting a "uart rx break" event.

The docs are a bit sparse in this area...what is a UART break? Does this seem like a configuration issue? I find it hard to believe the ESP32 UART can't swallow a message of a few hundred bytes without incident, so I'm inclined to think it's something I'm doing wrong.

Thanks...

Posted: **Tue Sep 18, 2018 4:04 pm**

A little more information: I modified my event handler (for experimentation) as follows:

Code: Select all

        if (xQueueReceive(m_uartQueue, (void *) &event, (portTickType)portMAX_DELAY))
        {
            bzero(ioBuff, BUF_SIZE);
            ESP_LOGI(TAG, "uart[%d] event:", CD_UART_NBR);
            switch(event.type)
            {
            // Event of UART receving data; need to handle fast.
            case UART_DATA:
                uart_get_buffered_data_len(CD_UART_NBR, &bufSize);
                ESP_LOGI(TAG, "%d bytes in SIO input buffer.", bufSize);
//                nbrBytesRead = (size_t) uart_read_bytes(CD_UART_NBR, ioBuff, bufSize, portMAX_DELAY);
                nbrBytesRead = (size_t) uart_read_bytes(CD_UART_NBR, ioBuff, 64, 0);
                ESP_LOGI(TAG, "%d bytes read in from SIO input buffer.", nbrBytesRead);
                uart_get_buffered_data_len(CD_UART_NBR, &bufSize);
                nbrBytesRead = (size_t) uart_read_bytes(CD_UART_NBR, ioBuff, bufSize, 0);
                ESP_LOGI(TAG, "%d bytes in SIO input buffer.", bufSize);
                for (unsigned int i = 0; i < bufSize; ++i)
                {
                    ESP_LOGI(TAG, "byte %d is %02x.", i, ioBuff[i]);
                }

I get this output:

I (104433) UART: uart[1] event:
I (104433) UART: 65 bytes in SIO input buffer.
I (104433) UART: 64 bytes read in from SIO input buffer.
I (104443) UART: 3 bytes in SIO input buffer.
I (104443) UART: byte 0 is 00.
I (104453) UART: byte 1 is 00.
I (104453) UART: byte 2 is 00.

The message being sent is 85 bytes, all printable ASCII characters. I'm at a loss for why the UART can't read that in one piece.

Posted: **Tue Sep 18, 2018 7:53 pm**

Would it be possible to post the complete fragment of logic showing all the UART processing including queue creation and other parts? Maybe post that as a GIT GIST fragment or some other link?

Posted: **Tue Sep 18, 2018 8:08 pm**

Hi, Neil - I hope I did this correctly (never used GISTs before):

https://gist.github.com/mzimmers/9ed4ea ... 17dba748d3

Thanks...

Posted: **Thu Sep 20, 2018 7:03 pm**

I'm making progress on this, but I now seem to be running into a hard limit of 120 bytes for a single read operation.
I'm using the uart event queue as demonstrated in the uart_events example, and my reads always stop at 120 bytes. If the message is in fact longer, a second UART_DATA event is delivered, and the rest of the message comes through at this time.

Does anyone know why this is happening? I suppose it could be either a queue limitation, which seems doubtful, or a buffer size limitation in the UART driver.

Here's some of the relevant code:

Code: Select all

        err = uart_driver_install(CD_UART_NBR, BUF_SIZE, 0, 20, &m_uartQueue, 0);
        if (xQueueReceive(m_uartQueue, (void *) &event, (portTickType)portMAX_DELAY))
        {
            unsigned i = uxQueueMessagesWaiting(m_uartQueue);
             
            switch(event.type)
            {
            // Event of UART receving data; need to handle fast.
            case UART_DATA:
                uart_get_buffered_data_len(CD_UART_NBR, &bufSize);
                nbrBytesRead = (size_t) uart_read_bytes(CD_UART_NBR, ioBuff, bufSize, portMAX_DELAY);

bufSize and nbrBytesRead both return as 120, though the input is larger.

Thanks...

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