SuperFX Hello

GSU coprocessor boot diagnostic with SRAM tests and FMULT validation

Emulator Compatibility

Emulator	Status
Mesen2	✅ Recommended — detects the GSU correctly and runs SuperFX cleanly
bsnes	✅ Cycle-accurate; useful as a second reference
luna	✅ Detects and runs the GSU natively (used by the test harness)
snes9x	❌ Does not detect GSU despite correct header — example shows "GSU: NOT DETECTED"

Build & Run

cd $OPENSNES_HOME
make -C examples/chips/superfx_hello

Then open superfx_hello.sfc in luna (or any SNES emulator).

What You'll Learn

• Detecting the SuperFX (GSU) coprocessor via the VCR register ($303B)
• Launching a GSU program with the WRAM stub (CPU cannot read ROM while GSU runs)
• SRAM shared memory: byte writes (STB: $42, $55) and word write (STW: $BEEF)
• FMULT fixed-point multiplication validation (2.0×2.0=$4000, 1.5×3.0=$4800)
• Reading GSU registers (R0=$CAFE) after STOP

Status Codes

Value	Meaning
GSU VERSION: $04	GSU-2 detected (GSU-1=$03, MC1=$01)
R0 RESULT: $CAFE	GSU executed code correctly
SRAM[0,1]: $42 $55	STB byte writes to SRAM work
STW[2,3]: $BEEF	STW word write to SRAM works
2*2=$4000 1.5*3=$4800	FMULT 4.12 fixed-point validated

Modules Used

Module	Purpose
console	System initialization
sprite	OAM setup (required by consoleInit)
dma	DMA transfers
background	BG configuration
text	Diagnostic text display
superfx	GSU detection and communication