From f87fe618fd0b6cbd8a219a580b44df12f2017cdb Mon Sep 17 00:00:00 2001
From: Alex Janka <alex@alexjanka.com>
Date: Fri, 3 Feb 2023 08:54:29 +1100
Subject: [PATCH] vblank should be working

---
 src/main.rs          |  2 ++
 src/processor/mod.rs | 23 ++++++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/main.rs b/src/main.rs
index 643b1fe..ce353de 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -265,6 +265,8 @@ fn main() {
         reg,
         last_instruction: 0x0,
         last_instruction_addr: 0x0,
+        vblank_timer: 0.,
+        vblank_remaining: 0,
     };
     cpu_ram_init(&mut cpu);
     let mut cycle_num = 0;
diff --git a/src/processor/mod.rs b/src/processor/mod.rs
index c670ea7..94b99c7 100644
--- a/src/processor/mod.rs
+++ b/src/processor/mod.rs
@@ -23,6 +23,8 @@ pub struct CPU {
     pub reg: Registers,
     pub last_instruction: u8,
     pub last_instruction_addr: u16,
+    pub vblank_timer: f64,
+    pub vblank_remaining: u8,
 }
 
 // Hz
@@ -43,6 +45,12 @@ impl CPU {
             }
         }
 
+        if self.vblank_timer >= (1. / 59.7) {
+            self.vblank_timer = 0.;
+            self.vblank_remaining = 20;
+            self.memory.set(0xFF0F, set_bit(self.memory.get(0xFF0F), 0));
+        }
+
         verbose_println!(
             "exec {:#4X} from pc: {:#X}",
             opcode,
@@ -58,6 +66,15 @@ impl CPU {
     fn increment_timers(&mut self, cycles: u8) {
         let secs = (cycles * 4) as f64 / (CLOCK_SPEED * SPEEDUP);
 
+        self.vblank_timer += secs;
+        if self.vblank_remaining > 0 {
+            self.vblank_remaining = self.vblank_remaining.saturating_sub(cycles);
+            if self.vblank_remaining == 0 {
+                self.memory
+                    .set(0xFF0F, clear_bit(self.memory.get(0xFF0F), 0));
+            }
+        }
+
         self.memory.set(
             0xFF04,
             self.memory
@@ -245,8 +262,12 @@ fn get_bit(byte: u8, flag: u8) -> bool {
     return got > 0x0;
 }
 
+fn set_bit(byte: u8, flag: u8) -> u8 {
+    byte | (1 << flag)
+}
+
 fn clear_bit(byte: u8, flag: u8) -> u8 {
-    byte & (!(1 << flag as u8))
+    byte & (!(1 << flag))
 }
 
 fn rotate(byte: u8, direction: &Direction) -> (u8, bool) {