Mesen2 Lua Script: Namco Serial Checker Interface (SRAM)

NamcoSerial_SRAM.lua

-----------------------
-- Name: Namco Serial Checker Interface (SRAM)
-- Author: TakuikaNinja
-----------------------
-- Simulates a serial interface used by a few of Namco's FC/NES games which use battery-backed SRAM.
-- It attempts to receive/send data and verify it.
-- If successful, SRAM contents are then verified.
-- The screen colour is set to blue if successful, otherwise it attempts to reinitialise SRAM.
-- The screen colour is set to yellow if the reinitialisation succeeds, otherwise it is set to red.
--
-- Successfully tested on games including:
-- "Family Circuit '91 (Japan) (En).nes"
-- "Splatterworld_ROM.nes" (Unreleased)
-----------------------

local consoleType = emu.getState()["consoleType"]
if consoleType ~= "Nes" then
	emu.displayMessage("Script", "This script only works on the NES/FC.")
	return
end

bit = 0

function strobe(address, value)
	local currentBit = value & 1
	bit = currentBit
	emu.log("$4016.d0 = " .. currentBit)
end

DATA = 0x02 -- %00000010, bit 1

function poll(address, value)
	local output = value & ~DATA -- preserve unused bits
	local outBit = bit ~ 1 -- fetch bit and invert it
	output = (output | (outBit * DATA)) & 0xff -- compose & return final output
	emu.log("$4017.d1 = " .. outBit)
	return output
end

script = "Namco Serial Checker (SRAM)"
emu.displayMessage("Script", script)

emu.addMemoryCallback(strobe, emu.callbackType.write, 0x4016)
emu.addMemoryCallback(poll, emu.callbackType.read, 0x4017)