This topic provides a brief overview about USB bulk transfers. Josh wrote: Yes, you can try to just copy the existing file as you proposed.You need to change the value for "DefaultProduct" to "0x0032". I have for a long time been wanting to do a Custom USB class driver on the RT106x devices. If a device provides several ttyUSB ports the "active" port (used for the actual ppp connection) has interrupt transfer type contrary to bulk transfer type. I am trying to modify the usb_dev_bulk example code and use it in a proofofconcept application. It is the very first time that I develop uC code for USB. 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. You want to BULK transfer files, you need to download entire files to a USB stick?