diff --git a/cli/emulator.c b/cli/emulator.c
index 929ee2b..9f680b3 100644
--- a/cli/emulator.c
+++ b/cli/emulator.c
@@ -32,8 +32,8 @@ int main(int argc, char *argv[])
 
     cpu.pc = 0;
 
-    for (executed = 0; executed < 100000; executed++) {
-        cpu_step(&cpu);
+    for (executed = 0; executed < 1000000; executed++) {
+        dmg_step(&dmg);
     }
 
     rom_free(&rom);
diff --git a/src/cpu.c b/src/cpu.c
index 7c8b0c2..842d626 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -125,6 +125,7 @@ static void inc_with_carry(struct cpu *regs, u8 *reg)
 	(*reg)++;
 	if(*reg == 0)
 		set_flag(regs, FLAG_ZERO);
+    else clear_flag(regs, FLAG_ZERO);
 }
 
 static void dec_with_carry(struct cpu *regs, u8 *reg)
@@ -135,6 +136,7 @@ static void dec_with_carry(struct cpu *regs, u8 *reg)
 	(*reg)--;
 	if(*reg == 0)
 		set_flag(regs, FLAG_ZERO);
+    else clear_flag(regs, FLAG_ZERO);
 }
 
 static u8 rotate_left(struct cpu *regs, u8 reg)
@@ -179,6 +181,7 @@ static void xor(struct cpu *regs, u8 value)
 	regs->a ^= value;
 	if(regs->a == 0)
 		set_flag(regs, FLAG_ZERO);
+    else clear_flag(regs, FLAG_ZERO);
 	clear_flag(regs, FLAG_SIGN);
 	clear_flag(regs, FLAG_HALF_CARRY);
 	clear_flag(regs, FLAG_CARRY);
@@ -189,6 +192,7 @@ static void or(struct cpu *regs, u8 value)
 	regs->a |= value;
 	if(regs->a == 0)
 		set_flag(regs, FLAG_ZERO);
+    else clear_flag(regs, FLAG_ZERO);
 	clear_flag(regs, FLAG_SIGN);
 	clear_flag(regs, FLAG_HALF_CARRY);
 	clear_flag(regs, FLAG_CARRY);
@@ -199,6 +203,8 @@ static void and(struct cpu *cpu, u8 value)
     cpu->a &= value;
 	if(cpu->a == 0) {
 		set_flag(cpu, FLAG_ZERO);
+    } else {
+        clear_flag(cpu, FLAG_ZERO);
     }
     clear_flag(cpu, FLAG_SIGN);
     set_flag(cpu, FLAG_HALF_CARRY);
@@ -650,6 +656,7 @@ void cpu_step(struct cpu *cpu)
         case 0xbd: subtract(cpu, cpu->l, 0, 1); break;
         case 0xbe: subtract(cpu, read8(cpu, read_hl(cpu)), 0, 1); break;
         case 0xbf: subtract(cpu, cpu->a, 0, 1); break;
+        case 0xfe: subtract(cpu, read8(cpu, cpu->pc), 0, 1); cpu->pc++; break;
 
         // RST
         case 0xc7: push(cpu, cpu->pc); cpu->pc = 0x00; break;
@@ -689,11 +696,7 @@ void cpu_step(struct cpu *cpu)
         case 0xf0: // LDH A,(a8)
             cpu->a = read16(cpu, 0xff00 + read8(cpu, cpu->pc));
             cpu->pc++;
-        case 0xfe: // CP d8
-            if (cpu->a - read8(cpu, cpu->pc) > 0x80) {
-                set_flag(cpu, FLAG_SIGN);
-            }
-            cpu->pc++;
+            printf("scanline was %d\n", cpu->a);
             break;
         case 0xf2: // LD A,(C)
             cpu->a = read8(cpu, 0xff00 + cpu->c);
diff --git a/src/dmg.c b/src/dmg.c
index 02e45ed..df4e439 100644
--- a/src/dmg.c
+++ b/src/dmg.c
@@ -19,8 +19,7 @@ u8 dmg_read(void *_dmg, u16 address)
     struct dmg *dmg = (struct dmg *) _dmg;
     if (address < 0x100) {
         return dmg_boot_rom[address];
-    }
-    if (address < 0x4000) {
+    } else if (address < 0x4000) {
         return dmg->rom->data[address];
     } else if (address < 0x8000) {
         // TODO switchable rom bank
diff --git a/src/lcd.c b/src/lcd.c
index 0acaf2d..d482d1f 100644
--- a/src/lcd.c
+++ b/src/lcd.c
@@ -25,10 +25,6 @@ u8 lcd_read(struct lcd *lcd, u16 addr)
 
 void lcd_write(struct lcd *lcd, u16 addr, u8 value)
 {
-    if (addr == REG_LY) {
-        // writing to this register always resets it
-        value = 0;
-    }
     lcd->regs[addr - REG_LCD_BASE] = value;
 }