4.1.3.1 Mass Storage Device Implementation

The on-board debugger implements a highly optimized variant of the FAT12 file system with several limitations, partly due to the nature of FAT12 itself and optimizations made to fulfill its purpose for its embedded application.

The Curiosity Nano USB device is USB Chapter 9-compliant as a mass storage device but does not, in any way, fulfill the expectations of a general purpose mass storage device. This behavior is intentional.

When using the Windows operating system, the on-board debugger enumerates as a Curiosity Nano USB Device found in the disk drives section of the device manager. The CURIOSITY drive appears in the file manager and claims the following available drive letter in the system.

The CURIOSITY drive contains approximately one MB of free space and does not reflect the target device’s Flash size. When programming an Intel HEX file, the binary data are encoded in ASCII with metadata providing a vast overhead, so 1 MB is a trivially chosen value for disk size.

It is not possible to format the CURIOSITY drive. The filename may appear in the disk directory listing when programming a file to the target, which is merely the operating system’s view of the directory that, in reality, has not been updated. It is not possible to read out the file contents. Removing and replugging the board will return the file system to its original state, but the target will still contain the previously programmed application.

Copy a text file starting with “CMD:ERASE” onto the disk to erase the target device.

By default, the CURIOSITY drive contains several read-only files for generating icons as well as reporting status and linking to further information:

• AUTORUN.ICO – icon file for the Microchip logo
• AUTORUN.INF – system file required for Windows Explorer to show the icon file
• KIT-INFO.HTM – redirect to the development board website
• KIT-INFO.TXT – a text file containing details about the board’s debugger firmware version, board name, USB serial number, device, and drag-and-drop support
• STATUS.TXT – a text file containing the programming status of the board