Re: LibUSB Interrupt Transfer

[Peter S. <pe...@st...>]

jay.k wrote:
> I am writing a standalone driver for this device using LibUSB instead
> of using the UVC driver in the Linux Kernel.

Why?


> I am allocating interrupt transfers as follows
> 
> static struct libusb_transfer *allocate_int_transfer(libusb_device_handle
> *handle)
> {
> 
>   struct libusb_transfer *transfer = libusb_alloc_transfer(0);
>   if (!transfer)
>     printf("transfer alloc failure");
>  
>  
>   unsigned char int_buf[16];
>   libusb_fill_interrupt_transfer(transfer,handle,0x87, 
> 		 int_buf, sizeof(int_buf),interrupt_callback, NULL, 0); 
> 
>   return transfer;
> }

This is not valid. The memory buffer you provide does not exist
once this function has returned.


> My Callback function is this:
> 
> static void interrupt_callback(struct libusb_transfer *transfer)
> {
> 	printf("interrupt_callback status %d\n", transfer->status);
> 	libusb_submit_transfer(transfer);
> }

This is OK.


> I send the Interrupt transfer in my main loop as follows:
> 
>  struct libusb_transfer *int_transfer;
>   int_transfer = allocate_int_transfer(dev_handle);
> 
>   r = libusb_submit_transfer(int_transfer);
>   if (r < 0)
> 	  printf("interrupt submit fail %d\n", r); 

Also OK.


> I am basically trying to reverse engineer and emulate the behaviour of
> that code, and accordingly write my code, so I get the exact same
> behaviour.

Again, why?


> We need to set the bInterval of 8 instead of 128.

Why do you think so?


//Peter