USB device design for an embedded MCU

I am working on a product with an LPC1788 which needs the following USB features:

Firmware download (from host PC to device, not through a USB key).
File upload (from device to host).
Ideally we'd also be able to get some information from the device like serial number etc.

The device should only work with a custom Windows application, so simply using a mass-storage device as-is will not do. There are quite a lot of data to upload (200MB +), so using USB bulk transfers seem necessary to me.

What is the best way to approach this? I imagine I would need to create some sort of USB composite device(?). However, I was hoping to use nxpUSBlib or winUSB so I don't have to go through the Windows driver validation process.... What are my options? Perhaps there some way to make the mass-storage device invisible for Windows?

Thanks!

Dirk

Solution

I think you'll definitely want to go with a vendor specific bulk device and you can easily use WinUSB for all of this. This should be sufficient for everything you've specified here.

For your firmware loader I'd recommend looking at the DFU (device firmware update) specification. You'll probably want make some command for your device that when sent will cause it to reenumerate itself in to DFU mode for update (rather than a composite device that is always exposed - this restricts the issue of the other interface being in use while you're flashing your device). Then you can flash it and reset it so it will reenumerate as your vendor specific bulk device again.

I wouldn't recommend mucking with mass storage, from your requirements it will be better to implement your own protocol and create some application or DLL that consumes the WinUSB API to communicate with your device, including the firmware update.