From 1580a3ba2bc82c490a43c93bb7fe1be1b0ba7390 Mon Sep 17 00:00:00 2001
From: Shachar Shemesh <shachar@shemesh.biz>
Date: Sun, 22 Oct 2023 22:03:01 +0300
Subject: [PATCH] Initial implementation of 6522::Timer1

---
 mos6522.cpp | 45 +++++++++++++++++++++++++++++++++++++++++++++
 mos6522.h   | 13 +++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/mos6522.cpp b/mos6522.cpp
index 2c765a5..57118bd 100644
--- a/mos6522.cpp
+++ b/mos6522.cpp
@@ -2,6 +2,24 @@
 
 void Mos6522::main() {
     while(true) {
+        timer1--;
+
+        if( timer1==0 ) {
+            if( aux_ctrl_reg & (1<<7) ) {
+                if( timer1_int_armed )
+                    orb ^= 0x80;        // XXX check whether affects ORB on real chip
+            }
+
+            if( aux_ctrl_reg & (1<<6) ) {
+                set_intr( Interrupts::T1 );
+                timer1 = timer1_latch_high << 8 | timer1_latch_low;
+            } else {
+                if( timer1_int_armed ) {
+                    set_intr( Interrupts::T1 );
+                    timer1_int_armed = false;
+                }
+            }
+        }
         //systemClock.tick();
     }
 }
@@ -16,6 +34,17 @@ uint8_t Mos6522::read(Addr registerSelect) {
         return ddrb;
     case 0x03:
         return ddra;
+    case 0x04:
+        reset_intr( Interrupts::T1 );
+        return timer1 & 0xff;
+    case 0x05:
+        return timer1 >> 8;
+    case 0x06:
+        return timer1_latch_low;
+    case 0x07:
+        return timer1_latch_high;
+    case 0x0a:
+        return aux_ctrl_reg;
     }
 }
 
@@ -37,6 +66,22 @@ void Mos6522::write(Addr registerSelect, uint8_t data) {
         ddra = data;
         update_output_a();
         break;
+    case 0x04:
+    case 0x06:
+        timer1_latch_low = data;
+        break;
+    case 0x05:
+        timer1_latch_high = data;
+        timer1 = timer1_latch_high << 8 | timer1_latch_low;
+        reset_intr( Interrupts::T1 );
+        break;
+    case 0x07:
+        timer1_latch_high = data;
+        reset_intr( Interrupts::T1 );
+        break;
+    case 0x0a:
+        aux_ctrl_reg = data;
+        break;
     }
 }
 
diff --git a/mos6522.h b/mos6522.h
index e2e7cd5..b00f066 100644
--- a/mos6522.h
+++ b/mos6522.h
@@ -8,8 +8,18 @@ class Mos6522 {
     Mos6522Interface &interface_;
     SystemClock &systemClock_;
 
+    // Registers
     uint8_t orb = 0, irb = 0, ddrb = 0;
     uint8_t ora = 0, ira = 0, ddra = 0;
+
+    uint16_t timer1 = 0;
+    uint8_t timer1_latch_low = 0, timer1_latch_high = 0;
+    bool timer1_int_armed = false;
+
+    uint8_t aux_ctrl_reg = 0;           // ACR
+
+    enum class Interrupts { T1 };
+    uint8_t intr = 0;
 public:
     enum class Port { A=0, B=1 };
 
@@ -30,4 +40,7 @@ class Mos6522 {
 private:
     void update_output_a();
     void update_output_b();
+
+    void reset_intr( Interrupts intr );
+    void set_intr( Interrupts intr );
 };