From bc66be6c0643e6f82efd9d790b094322d7bfe7da Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 22 Feb 2022 17:10:52 -0600
Subject: [PATCH] feat: impelement a barebones SRAM

---
 src/Bus.zig         |  4 ++--
 src/bus/GamePak.zig | 13 ++++++++++---
 src/bus/Sram.zig    | 31 +++++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+), 5 deletions(-)
 create mode 100644 src/bus/Sram.zig

diff --git a/src/Bus.zig b/src/Bus.zig
index 70ab917..0c6d38d 100644
--- a/src/Bus.zig
+++ b/src/Bus.zig
@@ -138,7 +138,7 @@ pub fn read8(self: *const Self, addr: u32) u8 {
         0x0800_0000...0x09FF_FFFF => self.pak.get8(addr - 0x0800_0000),
         0x0A00_0000...0x0BFF_FFFF => self.pak.get8(addr - 0x0A00_0000),
         0x0C00_0000...0x0DFF_FFFF => self.pak.get8(addr - 0x0C00_0000),
-        0x0E00_0000...0x0E00_FFFF => std.debug.panic("Read from 0x{X:0>2} in Game Pak SRAM", .{addr}),
+        0x0E00_0000...0x0E00_FFFF => self.pak.sram.get8(addr - 0x0E00_0000),
 
         else => std.debug.panic("Tried to read from 0x{X:0>2}", .{addr}),
     };
@@ -153,7 +153,7 @@ pub fn write8(self: *Self, addr: u32, byte: u8) void {
         0x0400_0410 => log.info("Wrote 0x{X:0>2} to 0x{X:0>8}. Ignored", .{ byte, addr }),
 
         // External Memory (Game Pak)
-        0x0E00_0000...0x0E00_FFFF => log.err("Wrote 0x{X:0>2} to 0x{X:0>8} in Game Pak SRAM", .{ byte, addr }),
+        0x0E00_0000...0x0E00_FFFF => self.pak.sram.set8(addr - 0x0E00_0000, byte),
         else => std.debug.panic("Tried to write 0x{X:0>2} to 0x{X:0>8}", .{ byte, addr }),
     }
 }
diff --git a/src/bus/GamePak.zig b/src/bus/GamePak.zig
index 1697b90..de3deb7 100644
--- a/src/bus/GamePak.zig
+++ b/src/bus/GamePak.zig
@@ -1,13 +1,14 @@
 const std = @import("std");
 
+const Sram = @import("Sram.zig");
 const Allocator = std.mem.Allocator;
+const log = std.log.scoped(.GamePak);
 const Self = @This();
 
 title: [12]u8,
 buf: []u8,
 alloc: Allocator,
-
-const log = std.log.scoped(.GamePak);
+sram: Sram,
 
 pub fn init(alloc: Allocator, path: []const u8) !Self {
     const file = try std.fs.cwd().openFile(path, .{});
@@ -17,7 +18,12 @@ pub fn init(alloc: Allocator, path: []const u8) !Self {
     const buf = try file.readToEndAlloc(alloc, len);
     const title = parseTitle(buf);
 
-    const pak = Self{ .buf = buf, .alloc = alloc, .title = title };
+    const pak = Self{
+        .buf = buf,
+        .alloc = alloc,
+        .title = title,
+        .sram = try Sram.init(alloc),
+    };
     pak.parseHeader();
 
     return pak;
@@ -49,6 +55,7 @@ fn lookupMaker(slice: *const [2]u8) ?[]const u8 {
 
 pub fn deinit(self: Self) void {
     self.alloc.free(self.buf);
+    self.sram.deinit();
 }
 
 pub fn get32(self: *const Self, idx: usize) u32 {
diff --git a/src/bus/Sram.zig b/src/bus/Sram.zig
new file mode 100644
index 0000000..ae6705f
--- /dev/null
+++ b/src/bus/Sram.zig
@@ -0,0 +1,31 @@
+const std = @import("std");
+
+const Allocator = std.mem.Allocator;
+const log = std.log.scoped(.SRAM);
+const Self = @This();
+
+buf: []u8,
+alloc: Allocator,
+
+pub fn init(alloc: Allocator) !Self {
+    // FIXME: SRAM is more than just a 64KB block of memory
+    const buf = try alloc.alloc(u8, 0x10000);
+    std.mem.set(u8, buf, 0);
+
+    return Self{
+        .buf = buf,
+        .alloc = alloc,
+    };
+}
+
+pub fn deinit(self: Self) void {
+    self.alloc.free(self.buf);
+}
+
+pub fn get8(self: *const Self, idx: usize) u8 {
+    return self.buf[idx];
+}
+
+pub fn set8(self: *Self, idx: usize, byte: u8) void {
+    self.buf[idx] = byte;
+}