What is the minimum needed to implement a vendor device that works with libusb?

[linhz0hz]

Hi I am quite new in TinyUSB. I have worked out the simplest CDC example, but for my application I might need more control. I want to implement it with vendor device and libusb. ( I have done a simple version with CH32V307, but would rather port it to tinyusb which is portable). I think WebUSB example is the closest, and I also saw the rpi pico commit with usbd_app_driver_get_cb, but would there be a simpler bare-minimal example to introduce the use of vendor device with generic in/out bulk/interrupt endpoint, or how to properly use usbd_app_driver_get_cb?
Thanks!

[linhz0hz]

In the spirit of not waiting for someone else to solve my problem, I am trying to strip down webusb example.
Frist I see that the default / built-in drivers are recorded under tu_static usbd_class_driver_t const _usbd_driver[] in usbd.c. However different from other standard types, the callback function are all(?) unimplemented? So I need to implement these. However, I am confused about tud_vendor_control_xfer_cb specifically: I thought string descriptors are handled by tud_descriptor_string_cb, and is at the device level not on the interface level, but when I do not implement tud_vendor_control_xfer_cb, the string descriptors are not even read correctly and the USB device has error code 10. It seems to relate to not responding to VENDOR_REQUEST_MICROSOFT ? But do I still need that even if I do not need automatically select drivers?

There is only one control endpoint, so I imagined only request specific to this vendor interface will need tud_vendor_control_xfer_cb. Also I see in process_control_request vendor request is treated specially compared to similar callback of other drivers, why is that?

[linhz0hz]

If I need to implement something similar to vendor class, then I need to reference class/vendor_device.c and class/vendor_device.h as example drivers. One small thing I noticed though is that in the webusb example there is endpoint size 512, but the CFG_TUD_VENDOR_EPSIZE was not properly defined to support endpoint size 512 in tusb_config.h

[linhz0hz]

More specifically, what is the difference between init/reset/open? What I know now is that tud_rhport_init calls _init operation for each driver before calling device-specific dcd_init.

Also I see p_epbuf->epout and p_epbuf->epin are used to store the buffer for usb transactions, and if I do not rely on the streaming buffer of tusb I would copy their memory content directly. But I do not see where are those buffer address set. I guess the dcd will take the information and configure the hardware correctly? However can I use an endpoint directly without involving the stream interface?

[linhz0hz]

Digging a little further, it seems that dcd_edpt_xfer usbd_edpt_xfer is where the address is set? But for out transfer don't I need to set the buffer before the transfer happens? Is the correct thing to call usbd_edpt_xfer when _init? Or call usbd_edpt_xfer when _open/_reset?

[linhz0hz]

In the end what I am looking for is a vendor device with a mix of interrupt and bulk endpoints. Having some basic example / documentation / advise of how to handle these basic operations would be great.

[linhz0hz]

I am happy to summarize /document the solution if I find out how to do this in the end, but I think I need some help.

[linhz0hz]

I figured most things out. Here is some trimmed sample.
https://gist.github.com/linhz0hz/341f8953eb4f4ec0e9b383d844b4fd64

[HiFiPhile]

There is also a nice example which is @kkitayam's CMSIS-DAP dongle.

https://github.com/kkitayam/akiprobe/blob/main/src/cmsis_dap_device.c