Here is a list of all documented files with brief descriptions:

asm.h [code]	Assembly helper
bmp.h [code]	Software bitmap engine
config.h [code]
everdrive.h [code]	Everdrive support
fat16.h [code]	FAT16 file system support
font.h [code]	SGDK system Font
genesis.h [code]
genres.h [code]
joy.h [code]	General controller support
kdebug.h [code]	Gens KMod debug methods
libres.h [code]
maths.h [code]	Mathematical methods
maths3D.h [code]	3D math engine
memory.h [code]	Memory handling methods
psg.h [code]	PSG support
smp_null.h [code]
smp_null_pcm.h [code]
sound.h [code]	Audio / Sound stuff
sprite_eng.h [code]	Sprite engine
sram.h [code]	SRAM (Static RAM used for save backup) support
string.h [code]	String manipulations
sys.h [code]	Entry point unit / Interrupt callback / System
tab_cnv.h [code]
tab_vol.h [code]
tfcplay.h [code]	TFM Music Maker compiled data player (68000)
tile_cache.h [code]	SGDK Tile cache engine (tile VRAM management)
timer.h [code]	Timer support
tools.h [code]	Misc tools methods
types.h [code]	Types definition
vdp.h [code]	VDP main
vdp_bg.h [code]	VDP background plan support
vdp_dma.h [code]	VDP DMA support
vdp_pal.h [code]	VDP Palette support
vdp_spr.h [code]	VDP Sprite support
vdp_tile.h [code]	VDP General Tile / Tilemap operations
ym2612.h [code]	YM2612 support
z80_ctrl.h [code]	Z80 control
z80_mvsc.h [code]	Z80 MVS driver constantes
z80_vgm.h [code]	Z80 VGM driver