Getting using while using two CDC com ports

[siddhartha993549]

Hi all,

I am trying to implement two CDC COM ports using TinyUSB. Receiving data from the host to the device works fine, and I can see the data in the buffer. However, when I loop the same data back to the same COM port, after a few iterations one of the COM ports stops working (it can be either one, randomly).

For that port, the API tud_cdc_n_write_available(itf) keeps returning 0. I checked the USB log as well: the host is sending IN tokens, but the device is responding with NAKs only. I am using tud_cdc_n_write() and tud_cdc_n_write_flush() for transmitting data.

Could anyone explain why tud_cdc_n_write_available() keeps returning 0 for one of the ports, and what might cause this behavior?

[HiFiPhile]

Which MCU you are using ? On version 0.20 some code refactor was done for the CDC driver, please try if 0.19 works.

[siddhartha993549]

Thank you for your response. I am currently using TinyUSB version 0.18, and the logic I am trying to implement is shown below.

uint8_t buf[64];

// Get current free space for this CDC interface
uint32_t fifo_space = tud_cdc_n_write_available(CDC_PORT1);

    if (fifo_space > 0)
    {
        uart_buf_count = 0;

        // Copy form 1kb  rx buffer 
        while (uart_buf_count < fifo_space &&
               uart_buf_count < sizeof(uart_buf) &&
               buffer_get(&rx_buffer, &data))
        {
            buf[buf_count++] = data;
        }

        if (uart_buf_count > 0)
        {
            tud_cdc_n_write(CDC_PORT1, buf, buf_count);
            tud_cdc_n_write_flush(CDC_PORT1);
        }
    }

///Repeat the same for 2nd CDC Port

[siddhartha993549]

After some iterations, one CDC port always shows fifo_space = 0, so even when the host sends IN tokens, the device keeps NAKing and cannot transmit.

[HiFiPhile]

Which MCU are you using ?

Please enable logging to get more information, particularly if queued transfers are successfully finished:

Queue EP 81 with 64 bytes ...
USBD Xfer Complete on EP 81 with 64 bytes
Queue EP 02 with 64  bytes ...
USBD Xfer Complete on EP 02 with 64  bytes