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Problem with CDC class device using Freescale USB stack version 4.1.1

Question asked by Stephen Munnings on Mar 7, 2014
Latest reply on Mar 13, 2014 by Stephen Munnings

We are building a project using the Freescale USB stack version 4.1.1

In this project, we are using the USB CDC class to create a virtual com device with the KInetis using the USB Device Stack (not host).

All seems to work well as long as a human is typing on the host (windows) terminal (Tera-term).

However, when we attempt to do a file transfer (using XMODEM) things just stop working.

(We have this working through a real serial interface - in the same project with compile time selection between a real RS-232 serial port and the CDC USB device)

Using the debugger, we have been able to determine that the Processor Expert generated code is delivering the same 16-byte packet (first packet of the XMODEM first block) over and over and over (endlessly).

The callback routine passed into USB_Class_CDC_Init() is the routine being given the same 16-byte packet, endlessly.

This continues even when the host program has stopped trying to send any data.

When human typing is involved, the packets are much less than 16 bytes.  When XMODEM starts, it triggers the reception of 16 byte packets, and then we hit this endless loop.

A short follow of the return path shows that the packet buffer points to itself as the next packet buffer.

We did not follow the code path any further.