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LPCXpresso SDK Example VCOM loopback doesn't work correct

Question asked by dingelen on Jun 19, 2019
Latest reply on Sep 10, 2019 by dingelen


I'm starting a new development with the LPC55S69 and for starters I'm trying to get the VCOM USB working. So I've got the dev-board, downloaded the latest version of MCUXpresso (v11.0.0), the latest SDK (2.6.0) and opened some of the VCOM examples (lpcxpresso55s69_dev_cdc_vcom_bm, lpcxpresso55s69_dev_cdc_vcom_freertos) and started the debugging. All clean, no code changes.

After starting the application, I get a "USB device CDC virtual com demo" in the console and a new VCOM port is enumerated in Windows device manager. Now I open a serial port terminal (Putty, YAT, Terminal, Hercules, ...) connect and open the COM-port and send some characters. I would expect them to be looped back to the terminal but some strange stuff is happening.

Putting some break points in the function APPTask shows me that the characters are received, and send out again in the line:

error = USB_DeviceCdcAcmSend(s_cdcVcom.cdcAcmHandle, USB_CDC_VCOM_BULK_IN_ENDPOINT, s_currSendBuf, size);

No errors are reported.

- Putty seems to work without any problems.

- All other terminals can loopback nothing or one character or one string transmission. Afterwards the connection doesn't work anymore. The APPTask function is no longer reached, the terminal software is in an error state and to recover from this error, a restart of the debug has to be preformed and the terminal has to disconnect and reconnect again.

This is the case for ALL VCOM examples (BM, FREERTOS, LITE BM, Composite, ...)


Can anyone else verify this behaviour? Does anyone know where this is comming from?