fixed PPU scroll issue

src/main.rs

@@ -79,7 +79,7 @@ fn run_dbg(path: &str) {
     cpu.reset(&mut bus);
     let mut dumper = dump::Dumper::new();
     let mut renderer = PpmRenderer::new();          // <-- add this
-    let frames: u32 = 360;
+    let frames: u32 = 1800;
 
     for f in 0..frames {
         while !bus.frame_done() {

src/ppu.rs

@@ -179,7 +179,7 @@ impl Ppu {
 
     pub fn write(&mut self, cart: &mut Cartridge, addr: u16, val: u8) {
         match addr & 0x2007 {
-            0x2000 => self.ctrl = val,
+            0x2000 => { self.ctrl = val; self.t = (self.t & !0x0C00) | (((val & 0x03) as u16) << 10); },
             0x2001 => self.mask = val,
             0x2002 => {}                 // write ignored
             0x2003 => self.oamaddr = val,