AnsweredAssumed Answered

LPC4370 USB CDC VCOM Questions

Question asked by mtenw on Aug 11, 2016
Latest reply on Aug 31, 2016 by mtenw



I have been trying the usbd_rom_cdc_vcom example of lpcopen 2.12 on the LPC-Link2 board. I was able to send the data from the LPC-Link2 board to a USB host, both PC and Mac. However, the maximum TX packet size the vcom_write() (or USBD_API->hw->WriteEP()) seems to be capped at 16,384 bytes. When the vcom_write() is called to send 32,768 bytes, it returns 32,768. That means the data is successfully sent. However, the USB hosts (both PC and Mac) do not receive the 32,768 bytes of data. I have seen other discussion saying the maximum number of bytes in a packet is 64 bytes, but it is for a LPC1769 (See




1. What is the maximum packet size the vcom_write() can send on LPC4370 (LPC-Link2 board)? Can users adjust any settings to increase the maximum packet size?

2. To send high speed USB data to a USB host, some discussions recommended bulk transfer. What is the recommended example to start with? Both usbd_rom_cdc_vcom and usbd_rom_libusb use bulk transfer. Which one should be used?

3. What application is recommended on the USB host to capture the data? Or we need to write a customized application (e.g. based on libusb) to get better performance?


Thank you very much for the help!