Controller works

src/bus.rs

@@ -68,8 +68,13 @@ impl Bus for NesBus {
             0x0000..=0x1FFF => self.ram[(address & 0x07FF) as usize] = value,
             0x2000..=0x3FFF => self.ppu.write(&mut self.cart, address, value),
             0x4014 => self.ppu.oam_dma(&self.ram, value),
-            0x4016 => self.controller.write_strobe(value),
-            0x4017 => self.controller2.write_strobe(value),
+            0x4016 => {
+                // Real hardware: the $4016 strobe line (OUT0) drives BOTH controller ports.
+                // Games only ever pulse $4016, so controller 2 must latch from it too.
+                self.controller.write_strobe(value);
+                self.controller2.write_strobe(value);
+            }
+            0x4017 => {} // APU frame counter; it does not strobe the controllers
             0x6000..=0x7FFF => self.cart.write_prg_ram(address, value),
             0x8000..=0xFFFF => self.cart.write_prg(address, value),
             _ => {} // Everything else dropped for now

src/cpu.rs

@@ -20,6 +20,11 @@ pub struct Cpu {
     pub cycles: u64,
     irq_pending: bool,
     nmi_pending: bool,
+    pub hist: [(u16, u8, u8); 8],
+    pub hist_i: usize,
+    last_pc: u16,
+    entry: Option<(u16, u8, u8, u8, u8, u8, [(u16, u8, u8); 8])>,
+    check: Option<(u8, bool)>, // (A at $824F, BEQ $8255 taken) - SMB start-check probe
 }
 
 impl Cpu {
@@ -45,7 +50,8 @@ impl Cpu {
 
     // New and reset methods 
     pub fn new() -> Self {
-        Self { a: 0, x: 0, y: 0, sp: 0xFD, pc: 0, p: FLAG_UNUSED | FLAG_INTERRUPT, cycles: 0, irq_pending: false, nmi_pending: false } // kick stars a NES CPU
+        Self { a: 0, x: 0, y: 0, sp: 0xFD, pc: 0, p: FLAG_UNUSED | FLAG_INTERRUPT, cycles: 0, irq_pending: false, nmi_pending: false, 
+            hist: [(0, 0, 0); 8], hist_i: 0, last_pc: 0, entry: None, check: None, } // kick stars a NES CPU
     }
 
     pub fn reset(&mut self, bus: &mut impl Bus) {
@@ -104,6 +110,13 @@ impl Cpu {
     pub fn sp(&self) -> u8 { self.sp }
     pub fn p(&self) -> u8 { self.p }
     pub fn cycles(&self) -> u64 { self.cycles }
+    pub fn hist(&self) -> [(u16, u8, u8); 8] { self.hist }
+    pub fn take_entry(&mut self) -> Option<(u16, u8, u8, u8, u8, u8, [(u16, u8, u8); 8])> {
+        self.entry.take()
+    }
+    pub fn take_check(&mut self) -> Option<(u8, bool)> {
+        self.check.take()
+    }
 
     // shared interrumpt function
     fn interrupt(&mut self, bus: &mut impl Bus, vector: u16) -> u8 {
@@ -130,6 +143,23 @@ impl Cpu {
             return cycles;
         }
 
+        let in_loop = (0x8227..=0x822E).contains(&self.pc);
+        if in_loop && !(0x8227..=0x822E).contains(&self.last_pc) && self.entry.is_none() {
+            let recent = core::array::from_fn( |i| {
+                let idx = self.hist_i.wrapping_sub(i + 1) & 7;
+                self.hist[idx]
+            });
+            self.entry = Some((self.pc, self.a, self.x, self.y, self.sp, self.p, recent));
+        }
+        // Diagnostic: SMB's title Start check is `$8247: LDA $06FC; ORA $06FD; CMP #$10;
+        // $824F: BEQ $8255` (StartGame). At $824F, A == $10 means the press was seen.
+        if self.pc == 0x824F && self.check.is_none() {
+            self.check = Some((self.a, self.a == 0x10));
+        }
+        self.last_pc = self.pc;
+        self.hist[self.hist_i % 8] = (self.pc, self.y, self.sp);
+        self.hist_i += 1;
+
         let opcode: u8 = self.fetch(bus);
         let cycles = match opcode {
             // Jumps & subroutines

src/main.rs

@@ -13,6 +13,7 @@ use crate::cartridge::Cartridge;
 use crate::cpu::Cpu;
 use crate::render::{PpmRenderer, Renderer};
 use eframe::egui;
+use eframe::egui::debug_text::print;
 use crate::render::WindowRenderer;
 
 
@@ -23,8 +24,9 @@ fn main() {
         3 if args[1] == "blargg" => run_blargg(&args[2]),
         3 if args[1] == "dbg" => run_dbg(&args[2]),
         3 if args[1] == "gui" => run_gui(&args[2]),
+        3 if args[1] == "autotest" => run_autotest(&args[2]),
         2 => run_cart(&args[1]),
-        _ => eprintln!("usage: rnes [<rom> | blargg <rom> | dbg <rom> | gui <rom>]"),
+        _ => eprintln!("usage: rnes [<rom> | blargg <rom> | dbg <rom> | gui <rom> | autotest <rom>]"),
     }
 }
 
@@ -103,6 +105,50 @@ fn run_one_frame(bus: &mut NesBus, cpu: &mut Cpu) {
     bus.begin_frame();
 }
 
+// Headless scripted-input test: drives the controller exactly like the GUI does
+// (Controller.set_buttons), so SMB's title Start handling can be observed without
+// needing a window or a keyboard. Frame-accurate and reproducible.
+fn run_autotest(path: &str) {
+    let cart = Cartridge::from_file(path).unwrap();
+    let mut bus = NesBus::new(cart);
+    let mut cpu = Cpu::new();
+    cpu.reset(&mut bus);
+
+    let frames: u32 = 900;
+    let mut last_mode = 0u8;
+
+    for f in 0..frames {
+        // hold Start frames 120..300, release 300..420, press and hold again from 420
+        let buttons: u8 = if (120..300).contains(&f) || f >= 420 {
+            crate::input::BTN_START
+        } else {
+            0
+        };
+        bus.controller_mut().set_buttons(buttons);
+
+        run_one_frame(&mut bus, &mut cpu);
+
+        let fc = bus.ram()[(0x06FC & 0x7FF) as usize];
+        let fd = bus.ram()[(0x06FD & 0x7FF) as usize];
+        let m7a = bus.ram()[(0x074A & 0x7FF) as usize];
+        let tsk = bus.ram()[(0x0772 & 0x7FF) as usize];
+        let dt = bus.ram()[(0x07A2 & 0x7FF) as usize];
+        let mode = bus.ram()[(0x0770 & 0x7FF) as usize];
+
+        let check = match cpu.take_check() {
+            Some((a, taken)) => format!("CHECK A={a:02X} BEQ={:<5}", taken),
+            None => String::from("CHECK --          "),
+        };
+        println!(
+            "f={f:03} {check} $06FC={fc:02X} $06FD={fd:02X} mask={m7a:02X} task={tsk:02X} demo={dt:02X} mode={mode:02X}"
+        );
+        if mode != last_mode {
+            println!("f={f:03} *** MODE {last_mode:02X} -> {mode:02X} ***");
+            last_mode = mode;
+        }
+    }
+}
+
 struct GuiApp {
     bus: NesBus,
     cpu: Cpu,
@@ -123,9 +169,31 @@ impl eframe::App for GuiApp {
     // Non-UI work: emulation runs here, before painting.
     fn logic(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
         self.renderer.poll_input(self.bus.controller_mut());
+
+        if let Some((pc, a, x, y, sp, p, recent)) = self.cpu.take_entry() {
+            print!("ENTRY: pc={pc:04X} A={a:02X} X={x:02X} Y={y:02X} SP={sp:02X} P={p:02X} | pre:");
+            for &(rpc, ry, rsp) in &recent { print!(" {rpc:04X}(Y={ry:02X})"); }
+            println!();
+        }
+        if let Some((a, taken)) = self.cpu.take_check() {
+            let tsk = self.bus.ram()[(0x0772 & 0x7FF) as usize];
+            let dt = self.bus.ram()[(0x07A2 & 0x7FF) as usize];
+            println!("CHECK: A={a:02X} BEQ={taken} task={tsk:02X} demoTimer={dt:02X}");
+        }
+        // TEMP: watch SMB's joypad storage + game state + PC
+        let fc = self.bus.ram()[(0x06FC & 0x7FF) as usize];
+        let m7a = self.bus.ram()[(0x074A & 0x7FF) as usize];
+        let m70 = self.bus.ram()[(0x0770 & 0x7FF) as usize];
+        let st  = self.bus.ppu().status();
+        let h = self.cpu.hist();
+        println!("$06FC={fc:02X} mask=$074A={m7a:02X} $2002={st:02X} mode={m70:02X} \
+          A={:02X} X={:02X} Y={:02X} SP={:02X} PC={:04X}",
+         self.cpu.a(), self.cpu.x(), self.cpu.y(), self.cpu.sp(), self.cpu.pc());
+        print!("  hist(old->new): ");
+        for &(pc, y, sp) in &h { print!("{pc:04X}(Y={y:02X},SP={sp:02X})"); }
+        println!();
         run_one_frame(&mut self.bus, &mut self.cpu);
         self.renderer.present(self.bus.framebuffer(), 256, 240);
-        // cap at 60fps: one emulated frame per 16.67ms, not "as fast as possible"
         ctx.request_repaint_after(std::time::Duration::from_millis(16));
     }