Hello, I have been "playing" with the Keil USB HID example (the RV30 version of it, using RTL). I have changed the packet size to 64 bytes (in both the ARM code and the HID_Client1 program). The HID client program does the readfile and the writefile in two seperate threads, but occasionally the writefile thread will get stuck (hang) in the writefile function (the thread calls the writefile function 1 million times in a loop). The only way to get the control back, is to stop the HID client app and start it again. It will work ok again (without resetting the MCB2140 board). I'm not using overlapped I/O, would that maybe be a possible fix ? Have any of you experienced something similar, and/or have any additional informatation (I have Jan Axelson's USB book on it's way and I have ordered a hardware USB analyser, but it will take some time before they arrives....) Regards, Carsten