This topic provides a brief overview about USB bulk transfers. Your URB bulk read size must be an exact multiple of the endpoint's maximum packet size, so 600 bytes is probably not a valid read size.The only thing that gets the endpoint out of this condition is physically plugging it out and back into the computer (or hub). Each USB transfer is one packet, which can be up to 64 bytes if using bulk type. If you want to send more than 64 bytes, you have to use multiple packets. Bulk Transfers take up all the bandwidth that is available after the other transfers have finished. Format USB flash drive on your Windows system. The USB class has one interface (interface 0) and one configuration (configuration 1). It has 4 endpoints, 1 OUT and 3 IN endpoints. Reliable exchange of data is ensured at the hardware level using error detection.