it seems that as soon as data is ready for the host (such as when I use WriteFile to send a command to the HID in which I tell the HID to give back some data such as the port value) and the in packet ready bit is set, the host reads it (as confirmed by another USB interrupt) before ReadFile ever is called. ReadFile is later used to put this data into a buffer on the host. Is this the way it should happen? I would have expected the ReadFile call to cause the in interrupt.
So here is my problem: I have a GUI and HID that work well together. The HID can do I2C to another IC, and the GUI can tell the HID to do I2C just fine. Upon startup, the GUI reads data from the HID and gets a correct value (say, 0x49). Opening a second GUI to the same HID does the same initial data read from the HID and gets the correct value (say, 0x49; it should be the same as the first GUI s read). Now, if I go to the first GUI, and do an I2C read, the readback value is 0x49, which was the value that the 2nd GUI had requested from the HID. It seems that the HID puts this value on the in endpoint for all devices attached to it. Thus the 1st GUI incorrectly thinks that this is the correct value.
Per Jan Axelson s HID FAQ, "every open handle to the HID has its own report queue. Every report a device sends goes into all of the queues so multiple applications can read the same report." I believe this is my problem. How do I purge this and clear the endpoint before the 1st GUI does its request so that the correct value (which the HID does send per the debugger) gets through? I tried HidD_FlushQueue, but it keeps returning False (not working; keep getting "handle is invalid" errors, although the handle is valid per WriteFile/ReadFile success with the same handles). Any ideas?
Thanks!