[Libusb-win32-devel] usb_bulk_read() + usb_find_devices() = stalled USB?

[chen h. <ch...@xa...>]

Hi, folks:

I'm writing a small program sampling datas from a USB device. 

In one thread, I read USB data with the following line:
    		size = usb_bulk_read(apu_usb_dev, 0x81, buf, 320, 20);

In another thread, I check the availablity of that USB device by calling the
following function fired by a timer for every 3 seconds.

int  APU_USB_Ready(LPARAM lParam)
{
	struct usb_bus		* bus ;
	struct usb_device	* dev ;

	usb_find_devices();
	for (bus = usb_get_busses(); bus ; bus = bus -> next) {
		for (dev = bus -> devices; dev; dev = dev -> next) {
			if (dev -> descriptor.idVendor == 0x5345 &&
				dev -> descriptor.idProduct == 0x1234)
					return 1 ;
		}
	}
	return 0 ;
}

It works for 20-40 minutes, then suddenly, size, the return value of usb_bulk_read()
would get something less than zero, and the USB line is stalled. I checking the online
manual of usb_bulk_read() and couldn't get much information there.

Removed the call of APU_USB_Ready(), the program kept running for more than 5 hours without
getting any "less than 0" error from usb_bulk_read().

Is this a known problem?

Thanks