From 570ff8536caf59c157285331b0bbf85bbae864e3 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Fri, 21 Oct 2022 05:12:41 -0300
Subject: [PATCH] chore: resolve incorrect memory mirror in VRAM

+ stub GPIO registers on ROM Write
---
 src/bus/GamePak.zig | 25 ++++++++++++++++++-------
 src/ppu.zig         |  8 ++++++--
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/src/bus/GamePak.zig b/src/bus/GamePak.zig
index 2e7e5c5..4ae26fa 100644
--- a/src/bus/GamePak.zig
+++ b/src/bus/GamePak.zig
@@ -113,18 +113,29 @@ pub fn write(self: *Self, comptime T: type, word_count: u16, address: u32, value
         }
     }
 
-    log.err("Wrote {} {X:} to 0x{X:0>8}", .{ T, value, address });
+    switch (T) {
+        u32 => switch (address) {
+            0x0800_00C4 => log.err("Wrote {} 0x{X:} to I/O Port Data and Direction", .{ T, value }),
+            0x0800_00C6 => log.err("Wrote {} 0x{X:} to I/O Port Direction and Control", .{ T, value }),
+            else => {},
+        },
+        u16 => switch (address) {
+            0x0800_00C4 => log.err("Wrote {} 0x{X:} to I/O Port Data", .{ T, value }),
+            0x0800_00C6 => log.err("Wrote {} 0x{X:} to I/O Port Direction", .{ T, value }),
+            0x0800_00C8 => log.err("Wrote {} 0x{X:} to I/O Port Control", .{ T, value }),
+            else => {},
+        },
+        u8 => log.warn("Wrote {} 0x{X:} to 0x{X:0>8}, Ignored.", .{ T, value, address }),
+        else => @compileError("GamePak: Unsupported write width"),
+    }
 }
 
 fn get(self: *const Self, i: u32) u8 {
     @setRuntimeSafety(false);
+    if (i < self.buf.len) return self.buf[i];
 
-    if (i >= self.buf.len) {
-        const lhs = i >> 1 & 0xFFFF;
-        return @truncate(u8, lhs >> 8 * @truncate(u5, i & 1));
-    }
-
-    return self.buf[i];
+    const lhs = i >> 1 & 0xFFFF;
+    return @truncate(u8, lhs >> 8 * @truncate(u5, i & 1));
 }
 
 test "OOB Access" {
diff --git a/src/ppu.zig b/src/ppu.zig
index 9993fd0..c4b06ca 100644
--- a/src/ppu.zig
+++ b/src/ppu.zig
@@ -600,8 +600,12 @@ const Vram = struct {
     }
 
     fn mirror(address: usize) usize {
-        const addr = address & 0x1FFFF; // repeated in steps of 128KiB
-        return if (addr >= 0x18000) addr & 0x7FFF else addr; // 64K + 32K + 32K (abcc)
+        // Mirrored in steps of 128K (64K + 32K + 32K) (abcc)
+        const addr = address & 0x1FFFF;
+
+        // If the address is within 96K we don't do anything,
+        // otherwise we want to mirror the last 32K (addresses between 64K and 96K)
+        return if (addr < vram_size) addr else 0x10000 + (addr & 0x7FFF);
     }
 };