52840 USB CDC missed first byte in RX event

RE: 52840 USB CDC missed first byte in RX event

OPCODE — Wed, 05 Aug 2020 17:42:45 GMT

I have a similar issue with the SDK17 with

APP_USBD_CONFIG_EVENT_QUEUE_ENABLE = 0

APP_USBD_CONFIG_SOF_HANDLING_MODE = 2

On carriage return, the next character is lost.

static void cdc_acm_user_ev_handler(app_usbd_class_inst_t const * p_inst,
                                    app_usbd_cdc_acm_user_event_t event)
{
    app_usbd_cdc_acm_t const * p_cdc_acm = app_usbd_cdc_acm_class_get(p_inst);

    switch (event)
    {
        case APP_USBD_CDC_ACM_USER_EVT_PORT_OPEN:
        {
            /*Set up the first transfer*/
            ret_code_t ret = app_usbd_cdc_acm_read(&m_app_cdc_acm, m_cdc_data_array, 1); // necessary it seems
            //NRF_LOG_INFO("CDC ACM port opened");
            break;
        }

        case APP_USBD_CDC_ACM_USER_EVT_PORT_CLOSE:
            //NRF_LOG_INFO("CDC ACM port closed");
            break;

        case APP_USBD_CDC_ACM_USER_EVT_TX_DONE:
            break;

        case APP_USBD_CDC_ACM_USER_EVT_RX_DONE:
        {
            ret_code_t ret;
            nrf_gpio_pin_write(LED_2,0);
            do{
                    ret = app_usbd_cdc_acm_read(&m_app_cdc_acm, &m_cdc_data_array[buffer_available_idx++], 1);  
            }while (ret == NRF_SUCCESS);
            nrf_gpio_pin_write(LED_2,1);
            break;
        }
        default:
            break;
    }
}

In the main loop i have something like

        if (buffer_available_idx){
                app_usbd_cdc_acm_write(&m_app_cdc_acm, m_cdc_data_array, strlen(m_cdc_data_array));
                memset(m_cdc_data_array, 0, RECV_BUF_LEN);
                buffer_available_idx=0;
        }

If I type alot of characters they are all echoed fine by the above code. Only when I press carriage return, the next character after CR is lost. Tried this with 2 terminal programs.

Thanks!

RE: 52840 USB CDC missed first byte in RX event

Pertti Kasanen — Fri, 14 Feb 2020 14:13:18 GMT

I stumble into a similar problem, using SDK 16.0.0. After trying and failing with many experiments, I found a workaround that worked for me.
In my case the first RX worked fine but (seemingly somewhat depending on what was done in the processing of the RX), the next byte was missing form the next RX "lines" from USB. The processing did send data back to USB with app_usbd_cdc_acm_write()

Adding a app_usbd_cdc_acm_read_any() call to "case APP_USBD_CDC_ACM_USER_EVT_TX_DONE:" handling solved the issue and now I'm getting also the first character of the line.


        case APP_USBD_CDC_ACM_USER_EVT_TX_DONE:
            //bsp_board_led_invert(LED_CDC_ACM_TX);
            ret = app_usbd_cdc_acm_read_any(&m_app_cdc_acm,
                                        m_rx_buffer,
                                        1);
            break;

RE: 52840 USB CDC missed first byte in RX event

Vidar Berg — Wed, 30 Jan 2019 11:08:32 GMT

This is good to hear, thanks for confirming. The example has been tested quite extensively by the SDK team so I think it's likely that I too did something wrong when I tested it earlier.

RE: 52840 USB CDC missed first byte in RX event

Juan — Wed, 30 Jan 2019 10:14:57 GMT

Yes, it is working for me now. Actually, there was not a bug. It was a concept mistake. But now things are clear for me.

Thanks.

RE: 52840 USB CDC missed first byte in RX event

Vidar Berg — Wed, 30 Jan 2019 08:56:30 GMT

yqin15,drk_tg, @Juan, for some reason I'm not able to replicate this issue anymore, nor is the developer who is tasked with fixing it. This is how I'm testing it:

- First I build and program the example from SDK 15.2.0 using SES then open a separate serial terminal to view the debug log

- Use realterm serial client to send a text string through the nRF USB

- Check if all data gets received by inspecting the debug log

Please let me know if you are testing it differently so that I can try the same here.

Here's the .hex file used:

devzone.nordicsemi.com/.../usbd_5F00_cdc_5F00_acm_5F00_pca10056.hex

RE: 52840 USB CDC missed first byte in RX event

drk_tg — Tue, 15 Jan 2019 09:54:56 GMT

Hi,

Any updates about this issue? Will the patch be available in the next release of the SDK?

Best,

Chris

RE: 52840 USB CDC missed first byte in RX event

Juan — Mon, 07 Jan 2019 14:37:18 GMT

Hi,

I have the same problem reported by Brian. I have solved it with the "solution" you provided. However, you mention that this is not recommended.

Is there any recomended solution? We are developing a prototype and we would like to have a stable code as soon as possible.

Regards,

JuanFran

RE: 52840 USB CDC missed first byte in RX event

Vidar Berg — Tue, 13 Nov 2018 14:18:55 GMT

Hi Brian,

Was able to reproduce the exact same behavior here and it seems to be caused by a logical error in the app_usbd_cdc_acm.c->cdc_acm_rx_block_finished() implementation. It "worked" when I commented out the following lines:

// First buffer is full
p_cdc_acm_ctx->last_read = p_cdc_acm_ctx->bytes_read; //+ bytes_to_cpy;
p_cdc_acm_ctx->bytes_read = 0;
p_cdc_acm_ctx->bytes_left = bytes_read; // - bytes_to_cpy;
p_cdc_acm_ctx->p_copy_pos = p_cdc_acm_ctx->internal_rx_buf;// + bytes_to_cpy;

However, it breaks the buffer switching so would not suggest to make this change. I have reported it as a bug internally.

Regards,

Vidar