Cannot receive USB 'BULK in' packets on vendor device

[second-string]

Operating System

MacOS

Board

ESP32-S3-PICO-1, custom PCB

Firmware

Using tinyusb through the esp_tinyusb component. These are the relevant callbacks defined in my code:

void tud_vendor_tx_cb(uint8_t itf, uint32_t sent_bytes) {
    ESP_LOGI(TAG, "tx cb: %lu", sent_bytes);
}

void tud_vendor_rx_cb(uint8_t itf, uint8_t const *buffer, uint16_t bufsize) {
    ESP_LOGI(TAG, "%.*s", bufsize, buffer);
    tud_vendor_read_flush();
}

/* Handle a couple request bytes specifically, but mostly just ACKing */
bool tud_vendor_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request_t const *request) {
    bool retval = false;
    ESP_LOGI(TAG, "Control stage: 0x%02X", stage);
    switch (stage) {
        case CONTROL_STAGE_SETUP:
            switch (request->bRequest) {
                case 0x5:  // GetModemStat
                    return tud_control_xfer(rhport,
                                            request,
                                            ftdi_get_modem_stat_resp,
                                            sizeof(ftdi_get_modem_stat_resp));
                case 0x4:  // SetData
                    // xTimerStart(ftdi_bulk_timer, portMAX_DELAY);
                    retval = tud_control_status(rhport, request);
                    break;
                case 0x0A: {  // GetLatTimer
                    uint8_t latency = 16;
                    // xTimerStart(ftdi_bulk_timer, portMAX_DELAY);
                    return tud_control_xfer(rhport, request, &latency, 1);
                }
                default:
                    retval = tud_control_status(rhport, request);
                    break;
            }

            break;
        default:
            retval = true;
            break;
    }

    return retval;
}


### What happened ?

I am trying to implement emulation of an existing vendor device within my firmware. I have no issues setting up tinyusb to properly create a vendor device with the 2 bulk in and out endpoints. I can read and respond to all control messages as expected from the `tud_vendor_control_xfer_cb` callback. I can also see all data coming in as a 'BULK out' transfer from the host. For example, if I open the serial port with `screen <port>` and type characters, they show up as 'BULK out' packets in wireshark and the RX callback fires as expected.

My issue is that the host driver on the connected computer is sending 'BULK in' packets, but there is no indication in the firmware that anything is happening. I have enabled the most verbose logging possible at level 3 and also sprinkled my own print statements throughout tinyusb for tracing, but there is never anything printed when those packets are sent. I can see them in wireshark as "(submitted)", but they're never "(completed)". I'm not sure if I'm misunderstanding something about USB in general here, but I've gone fairly deep throughout all of the tinyusb code and cannot find any indication that the bytes are being seen/handled.

The enumeration of the device, along with the device descriptors / interface / endpoints matches the device I'm trying to emulate. The device is operating at USB full speed. The only issue seems to be that I can't see these packets to respond to them. I'm happy to provide wireshark captures or any other data necessary.

### How to reproduce ?

Using tinyusb within the espressif component wrapper. [This] shows that it's tinyusb 0.17 under the hood. I don't think this should be causing any issues as I'm registering as a vendor device and the endpoints all look solid to me. I will probably try with just stock tinyusb pulled into an example project instead of depending on the esp wrapper to see if it's still reproducible just in case.

### Debug Log as txt file (LOG/CFG_TUSB_DEBUG=2)

Log output isn't really helpful since the issue is that nothing is logged / nothing happens at the point that wireshark shows the 'URB_BULK in' packet fired.

### Screenshots

_No response_

### I have checked existing issues, dicussion and documentation

- [X] I confirm I have checked existing issues, dicussion and documentation.

[HiFiPhile]

connected computer is sending 'BULK in' packets

IN packets are sending from the device to host, in opposite of OUT packet.

https://www.beyondlogic.org/usbnutshell/usb4.shtml#Bulk

What you see URB_BULK in is only the request that the host is ready to receive (sending IN token).

Without sending anything with tud_vendor_write() tud_vendor_write_flush() of cause the sending complete callback tud_vendor_tx_cb() wont be called.

[second-string]

Thanks for the helpful link. I had a feeling this was the case and I was just misunderstanding, but the way that wireshark displays the URBs was messing with my thinking. Even though the data is driven from the device, wireshark will slide the URB_IN RX (submitted) in before the data returned from the device, since it was just a request to the internal host peripheral for more data if available.

I was also very confused because I didn't see why the device I was emulating would be spamming 2 byte packets back to the host every 16ms with nothing from the host telling it to, but I eventually found documentation that explained that the device has an internal 16ms timeout where it will always send its status as a 'keep-alive' if no other data had been transmitted back to the host in 16ms.

Sorry it took a while for me to get back to this - thank you for the help understanding!