Mass Storage Device Implementation

The on-board debugger implements a highly optimized variant of the FAT12 file system that has 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 that can be found in the disk drives section of the device manager. The CURIOSITY drive appears in the file manager and claims the next available drive letter in the system.

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

It is not possible to format the CURIOSITY drive. When programming a file to the target, the filename may appear in the disk directory listing. This is merely the operating system’s view of the directory, which, 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 application that has been previously programmed.

To erase the target device, copy a text file starting with “CMD:ERASE” onto the disk.

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

Info: STATUS.TXT is dynamically updated by the on-board debugger. The contents may be cached by the OS and, therefore, do not reflect the correct status.