USB Tx sending 4096 byte chunk from FIFO

Hello Ti Support Team,

I have a Problem with my USB application. I am using a CDC connection based on the StarterWare example usb_dev_serial. The communication seems to be ok but then, under an unknown condition, my USB Tx stops sending the telegrams in small blocks. Instead the USB FIFO seems to swallow all the data and finally spits out a chunk of 4096 bytes. I can interrupt this collecting by sending a telegram from the host (PC). Then my USB device sends the currently collected data in the FIFO. I am not sure if the data is collected in the FIFO, or what exactly is going on. But what I see is that USBEndpointDataPut and USBEndpointDataSend are called continuesly, but the data is not coming out. Any ideas what this behavior is caused from?

I verified that the FIFOs are configured to 64 bytes (in FS and HS).
I tested this with FullSpeed, HighSpeed, Cppi41DMA on and off, data caches on and off. All the same result.

Test environment:
- CCS Studio 5.5
- StarterWare 02_00_01_01
- Beagleboneblack with USB0
- Windows7 64bit with an USB data monitor

Thanks in advance,
Stephan