USB modes - individual vs composite mode for devices

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The goal is to set up a device like SD card or eMMC (flash memory chip on PCB) as both a mountable (in Windows) volume and as a communication device (CDC).

This is possible (I have read) by setting up a composite device in USB


Working with a SAM4E dev board, I created two projects. I wanted to make sure I could mount an SD card before moving on to the composite functionality.

One is using USB mass storage as a single device (choose USB device project and select mass_storage from pull-down).

The other is using USB device, but select "composite" from the pull-down and then from the sub menus, choose mass_storage.


The first project builds and runs. Inserting an SD card opens a window on the PC and shows the root directory of the card.

The second project builds and runs, but there is no response to inserting an SD card.


How do I get the SD card to be recognized in composite mode?

Is it all in the setup? Which structures or other settings are critical in this setup?


Thanks for any help.


I am using the SAM4E-EK dev board for now, but will be moving the project to another board (SAM4E16E chip) later.