Hi Li,
If you are starting a new USB-based application, it is recommended considering a newer LPC device, because LPC2xxx are now legacy devices.
Regarding zero-length packet, it may depend of the used USB stack; you could take a look at the following links for reference:
https://github.com/micromint/LPCOpen-keil-lpc43xx/blob/master/applications/lpc18xx_43xx/examples/usb...
http://www.keil.com/forum/16271/arm7-lpc2148-amp-usb-communication/
https://www.nxp.com/docs/en/application-note/AN10703.pdf
Hope this will be useful for you.
Best regards!
/Carlos
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