From e693ad8a3c3674cd1ca78846dbb7d802bfd2a927 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sun, 3 Jan 2021 01:21:19 -0600
Subject: [PATCH] feat: create timer struct and stub 0xff07

---
 src/bus.rs   | 13 ++++++++--
 src/lib.rs   |  1 +
 src/timer.rs | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 80 insertions(+), 2 deletions(-)
 create mode 100644 src/timer.rs

diff --git a/src/bus.rs b/src/bus.rs
index 8e84fd4..ffba980 100644
--- a/src/bus.rs
+++ b/src/bus.rs
@@ -1,5 +1,6 @@
 use super::cartridge::Cartridge;
 use super::ppu::PPU;
+use super::timer::Timer;
 use super::work_ram::{VariableWorkRAM, WorkRAM};
 #[derive(Debug, Clone)]
 pub struct Bus {
@@ -8,6 +9,7 @@ pub struct Bus {
     ppu: PPU,
     wram: WorkRAM,
     vwram: VariableWorkRAM,
+    timer: Timer,
 }
 
 impl Default for Bus {
@@ -18,6 +20,7 @@ impl Default for Bus {
             ppu: Default::default(),
             wram: Default::default(),
             vwram: Default::default(),
+            timer: Default::default(),
         }
     }
 }
@@ -86,7 +89,10 @@ impl Bus {
             0xFEA0..=0xFEFF => unimplemented!("{:#06X} is not allowed to be used", addr),
             0xFF00..=0xFF7F => {
                 // IO Registers
-                unimplemented!("Unable to read {:#06X} in I/O Registers", addr);
+                match addr {
+                    0xFF07 => self.timer.control.into(),
+                    _ => unimplemented!("Unable to read {:#06X} in I/O Registers", addr),
+                }
             }
             0xFF80..=0xFFFE => {
                 // High RAM
@@ -139,7 +145,10 @@ impl Bus {
             0xFEA0..=0xFEFF => unimplemented!("{:#06X} is not allowed to be used", addr),
             0xFF00..=0xFF7F => {
                 // IO Registers
-                unimplemented!("Unable to write to {:#06X} in I/O Registers", addr);
+                match addr {
+                    0xFF07 => self.timer.control = byte.into(),
+                    _ => unimplemented!("Unable to write to {:#06X} in I/O Registers", addr),
+                };
             }
             0xFF80..=0xFFFE => {
                 // High RAM
diff --git a/src/lib.rs b/src/lib.rs
index 5d4215f..266f13d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,4 +3,5 @@ mod cartridge;
 pub mod cpu;
 mod instruction;
 mod ppu;
+mod timer;
 mod work_ram;
diff --git a/src/timer.rs b/src/timer.rs
new file mode 100644
index 0000000..a1f1fd9
--- /dev/null
+++ b/src/timer.rs
@@ -0,0 +1,68 @@
+#[derive(Debug, Clone, Copy)]
+pub struct Timer {
+    pub control: TimerControl,
+}
+
+impl Default for Timer {
+    fn default() -> Self {
+        Self {
+            control: 0x00.into(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+enum TimerSpeed {
+    Freq4096Hz,
+    Freq262144Hz,
+    Freq65536Hz,
+    Freq16384Hz,
+}
+
+impl From<u8> for TimerSpeed {
+    fn from(byte: u8) -> Self {
+        match byte {
+            0x00 => Self::Freq4096Hz,
+            0x01 => Self::Freq262144Hz,
+            0x10 => Self::Freq65536Hz,
+            0x11 => Self::Freq16384Hz,
+            _ => unreachable!(),
+        }
+    }
+}
+
+impl From<TimerSpeed> for u8 {
+    fn from(speed: TimerSpeed) -> Self {
+        match speed {
+            TimerSpeed::Freq4096Hz => 0x00,
+            TimerSpeed::Freq262144Hz => 0x01,
+            TimerSpeed::Freq65536Hz => 0x10,
+            TimerSpeed::Freq16384Hz => 0x11,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct TimerControl {
+    enabled: bool,
+    speed: TimerSpeed,
+}
+
+impl From<u8> for TimerControl {
+    fn from(byte: u8) -> Self {
+        let byte = byte & 0x07; // Clear everything but last 3 bits
+
+        Self {
+            enabled: (byte >> 2) == 0x01,
+            speed: (byte & 0x03).into(), // Clear everything but last 2 bits
+        }
+    }
+}
+
+impl From<TimerControl> for u8 {
+    fn from(control: TimerControl) -> Self {
+        let byte: u8 = control.speed.into(); // Get bit 1 and 0.
+
+        (byte & !(1u8 << 2)) | ((control.enabled as u8) << 2) // specifically manibulate bit 2
+    }
+}