File System

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The Prizm has two separate file systems, in RAM and in Flash.

Main Memory #

The Main Memory is a 61KB region in the RAM (with multiple backed up versions in Flash, possibly in a rolling setup) that is used for saving config files, programs, and other data that is modified often. Casio calls it the MCS, possibly an acronym for “Main Content System”.

Files in the MCS can have any kind of content, but they do not have an extension. Using the default OS means, users can’t directly control what each file contains, nor create arbitrary files (except for programs, which can have relatively arbitrary content), nor decide in which folder files go - even when connecting through USB, the contents of the @MainMem abstraction are not directly mapped to the contents of the MCS!

Folders are supported, but sub-folders are not. Rather than a full file system, the MCS can be thought of as a key-value store, or an associative array, where each key is the conjunction of the folder name and the file name (but keep in mind that, internally, it is not stored as a traditional C array!).

One can inspect the true, unfiltered contents of the MCS using an add-in like Insight or the TestMode. It will show up a bunch of folders not normally visible, some because they are empty and others because they are system folders. It will also show that the user-facing MCS browsers filter a lot of things and even rename some folders: for example, the “system” folder, where BASIC programs are located, is shown with the name of “PROGRAM”.

The MCS_* functions are used to access the Main Memory.

Storage Memory #

The Storage Memory is a 16MB region in flash that contains data in many formats. When the Prizm is connected via a USB cable, the Storage Memory is presented (along with a folder for limited access to the Main Memory) as a USB drive.

The filesystem in the Storage Memory is a FAT16 with a directory structure very similar to PC DOS. Directories do not reside at fixed memory positions. The filesystem used is the Fugue Flash filesystem from Kyoto Software Research; the following string can be found the a Prizm at various memory locations: “Fugue FAT File System 2004-03-03 00:00”. A PDF about this filesystem can be found here: 1.

The Bfile_* functions are used to access files in the Storage Memory. For Bfile_* functions, you must start off all paths with “\\fls0\” (which is a special prefix that specifies that the built-in filesystem will be used). Note that in C, the escaped form would be “\\\\fls0\\”. While the Prizm doesn’t at this point have the ability to interact with SD cards, the prefix for accessing the filesystem contained on one would be “\\crd0\”, or “\\\\crd0\\” in C.