everdrive-fat

FAT filesystem driver and stdio-like interface for the Turbo Everdrive flash card (http://krikzz.com/) for the NEC PC-Engine and TurboGrafx 16 video game consoles.

The FAT library is implemented in C (using the Small-C subset as provided by the HuC compiler), and leverages the low level Everdrive SD driver written by https://github.com/BlockoS. My work would not have been possible without that driver.

Overview

The main FAT library consists of the following C library files:

src/

• fat-dev.h - Implements low level and partition detection routines.
• fat-vol.h - Implements FAT volume sector information retrieval for the current selected partition.
• fat-files.h - Implements fopen() and fclose() - planned implementation for fread(), fseek() etc.
• fat-misc.h - Helper and test functions, will not be needed in production use of the fat library.
• fat.h - Macro importing all the fat library files, several global variables and constants.

In addition, the following files include helper functions that, while not directly related to FAT/Filesystem support, are required:

• math32.h - Several 32bit math functions - add/multiply etc, needed for 32bit sector addressing.
• math32-extras.h - Logical operators/tests for 32bit numbers.
• endian.h - Functions to flip 16 and 32bit data structures from little to big-endian as needed for FAT devices.
• print.h - Functions to print 32bit values as text/hex.

You can find example implementations of the everdrive-fat library under:

examples/

• test-detect.c - Detailed SD card detection, partition identifier and FAT filesystem info, demonstrates the fat-dev.h, fat-vol.h functions.
• test-files.c - Example code for testing the functionality of fopen() and fread() as included in fat-files.h.
• test-textreader.c - Not yet implemented.
• test-speed.c - Example code for testing the speed of reading sectors from the SD card.

To include the driver in your game/utility, copy the contents of the 'src' directory and include "fat.h" in your main code. Take a look at the examples for useage details.

Documentation is available for all functions within the relevant header files, further documentation will appear in:

docs/

Current Status

Code has been tested on both physical and emulated systems: a Turbo Express with Everdrive (along with SD and SDHC cards) as well as Mednafen (for general correctness and debugging).

I currently use HuC/PCEAS v3.21.

The fat library can currently do the following:

• SD Card / Turbo Everdrive - Can detect the Turbo Everdrive flash card and the inserted SD card (and type)
• DOS Master Boot Record - Can autodetect the first available FAT partition and extract start sector information, setting it as the current partition for a given session. Can also choose partition 1-4 manually, setting it as current for a session.
• FAT Volume Record - Can read FAT volume sector information, reading sector/cluster sizes, FAT table starting addresses and data cluster start, resulting in the starting address of the root directory cluster for the filesystem.
• Directories - Directory traversal to find named files/folders is implemented and working via the fopen() call.
• Files - Initial file (read) support is implemented in fread(). For now only the first 512 bytes of a file can be read as the file pointer and get-next-sector logic in not implemented.

Feedback

Email me, or post in the PCEngineFX forums: http://www.pcenginefx.com/forums/index.php?topic=15996.0