What is the purpose of the word 'rom' in LPC open USB related subdirectories?

[ankurgohel]

We are using lpcopen_2_18_lpcxpresso_nxp_lpcxpresso_1837. Some of the USB related directories have names of the type usbd_rom_cdc_uart, usbd_rom_cdc_vcom and usbd_rom_dfu_composite. The presence of word ROM confused us a bit. Can someone shed some light on the purpose of the word ROM and whether or not these applications can be used on RAM like other sample applications?lpcopen #lpc1837 #lpc1820

[bernhardfink]

In this LPC1800 chip architecture we have integrated quite some code into a ROM mask, so besides the boot ROM there is also code for USB inside. You don't see the source code for it in LPCOpen, only the API definition. When you for example use the DFU boot mode the bootloader jumps into the USB part of the ROM code to set up a DFU connection to a host.

The advantage of the ROM code is that it runs faster and more efficient than from internal flash and of course it doesn't use any program space in internal flash.

So if you use these examples from LPCOpen, then this means that the code jumps into ROM code for specific functions, you can't change this code and you can't perform debugging on source code level. Your main file or other code you add can be of course in RAM or in flash.

Regards,

NXP Support Team