From 92cabd248b6e907ae720272227dbf7991f588dd4 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Thu, 14 Apr 2022 01:58:40 -0300
Subject: [PATCH] chore: improve timer behaviour

---
 src/bus/io.zig    |  8 ++++----
 src/bus/timer.zig | 28 ++++++++++++++++------------
 2 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/src/bus/io.zig b/src/bus/io.zig
index 73a3d83..35e4508 100644
--- a/src/bus/io.zig
+++ b/src/bus/io.zig
@@ -268,13 +268,13 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_00DE => bus.dma._3.writeCntHigh(value),
 
             // Timers
-            0x0400_0100 => bus.tim._0.writeCntLow(value),
+            0x0400_0100 => bus.tim._0.setReload(value),
             0x0400_0102 => bus.tim._0.writeCntHigh(value),
-            0x0400_0104 => bus.tim._1.writeCntLow(value),
+            0x0400_0104 => bus.tim._1.setReload(value),
             0x0400_0106 => bus.tim._1.writeCntHigh(value),
-            0x0400_0108 => bus.tim._2.writeCntLow(value),
+            0x0400_0108 => bus.tim._2.setReload(value),
             0x0400_010A => bus.tim._2.writeCntHigh(value),
-            0x0400_010C => bus.tim._3.writeCntLow(value),
+            0x0400_010C => bus.tim._3.setReload(value),
             0x0400_010E => bus.tim._3.writeCntHigh(value),
             0x0400_0110 => {}, // Not Used
 
diff --git a/src/bus/timer.zig b/src/bus/timer.zig
index 012e469..d68f9fe 100644
--- a/src/bus/timer.zig
+++ b/src/bus/timer.zig
@@ -33,7 +33,7 @@ fn Timer(comptime id: u2) type {
         /// Read Only, Internal. Please use self.counter()
         _counter: u16,
 
-        /// Write Only, Internal. Please use self.writeCntLow()
+        /// Write Only, Internal. Please use self.setReload()
         _reload: u16,
 
         /// Write Only, Internal. Please use self.WriteCntHigh()
@@ -56,18 +56,17 @@ fn Timer(comptime id: u2) type {
         }
 
         pub fn counter(self: *const Self) u16 {
-            if (self.cnt.cascade.read())
-                return self._counter
-            else
-                return self._counter +% @truncate(u16, (self.sched.now() - self._start_timestamp) / self.frequency());
+            if (self.cnt.cascade.read() or !self.cnt.enabled.read()) return self._counter;
+
+            return self._counter +% @truncate(u16, (self.sched.now() - self._start_timestamp) / self.frequency());
         }
 
         pub fn writeCnt(self: *Self, word: u32) void {
-            self.writeCntLow(@truncate(u16, word));
+            self.setReload(@truncate(u16, word));
             self.writeCntHigh(@truncate(u16, word >> 16));
         }
 
-        pub fn writeCntLow(self: *Self, halfword: u16) void {
+        pub fn setReload(self: *Self, halfword: u16) void {
             self._reload = halfword;
         }
 
@@ -77,13 +76,18 @@ fn Timer(comptime id: u2) type {
             // If Timer happens to be enabled, It will either be resheduled or disabled
             self.sched.removeScheduledEvent(.{ .TimerOverflow = id });
 
-            if (!self.cnt.enabled.read() and new.enabled.read()) {
-                // Reload on Rising edge
-                self._counter = self._reload;
-
-                if (!new.cascade.read()) self.scheduleOverflow(0);
+            if (self.cnt.enabled.read() and (new.cascade.read() or !new.enabled.read())) {
+                // Either through the cascade bit or the enable bit, the timer has effectively been disabled
+                // The Counter should hold whatever value it should have been at when it was disabled
+                self._counter +%= @truncate(u16, (self.sched.now() - self._start_timestamp) / self.frequency());
             }
 
+            // The counter is only reloaded on the rising edge of the enable bit
+            if (!self.cnt.enabled.read() and new.enabled.read()) self._counter = self._reload;
+
+            // If Timer is enabled and we're not cascading, we need to schedule an overflow event
+            if (new.enabled.read() and !new.cascade.read()) self.scheduleOverflow(0);
+
             self.cnt.raw = halfword;
         }