kc85 wip

src/common/common.zig

@@ -3,3 +3,4 @@ pub const memory = @import("memory.zig");
 pub const glue = @import("glue.zig");
 pub const clock = @import("clock.zig");
 pub const filter = @import("filter.zig");
+pub const utils = @import("utils.zig");

src/common/utils.zig

@@ -0,0 +1,29 @@
+const std = @import("std");
+const assert = std.debug.assert;
+
+// shorthand for std.mem.copyForwards
+pub fn cp(src: []const u8, dst: []u8) void {
+    std.mem.copyForwards(u8, dst, src);
+}
+
+// 32-bit xorshifter
+pub fn xorshift32(in_x: u32) u32 {
+    var x = in_x;
+    x ^= x << 13;
+    x ^= x >> 17;
+    x ^= x << 5;
+    return x;
+}
+
+pub fn fillNoise(slice: []u8, seed: u32) u32 {
+    assert((slice.len & 3) == 0);
+    var x = seed;
+    for (0..(slice.len >> 2)) |i| {
+        x = xorshift32(x);
+        slice[i * 4] = @truncate(x);
+        slice[i * 4 + 1] = @truncate(x >> 8);
+        slice[i * 4 + 2] = @truncate(x >> 16);
+        slice[i * 4 + 3] = @truncate(x >> 24);
+    }
+    return x;
+}

src/systems/bombjack.zig

@@ -7,6 +7,7 @@ const common = @import("common");
 const memory = common.memory;
 const clock = common.clock;
 const pin = common.bitutils.pin;
+const cp = common.utils.cp;
 const AudioCallback = common.glue.AudioCallback;
 const AudioOptions = common.glue.AudioOptions;
 const DisplayInfo = common.glue.DisplayInfo;
@@ -842,10 +843,6 @@ pub const Bombjack = struct {
         self.main_board.palette[pal_index] = c;
     }
 
-    fn cp(src: []const u8, dst: []u8) void {
-        std.mem.copyForwards(u8, dst, src);
-    }
-
     fn initMainRom(opts: Options) [5][0x2000]u8 {
         var rom: [5][0x2000]u8 = undefined;
         cp(opts.roms.main_0000_1FFF, &rom[0]);

src/systems/kc85.zig

@@ -9,6 +9,8 @@ const common = @import("common");
 const memory = common.memory;
 const clock = common.clock;
 const pin = common.bitutils.pin;
+const cp = common.utils.cp;
+const fillNoise = common.utils.fillNoise;
 const AudioCallback = common.glue.AudioCallback;
 const AudioOptions = common.glue.AudioOptions;
 const DisplayInfo = common.glue.DisplayInfo;
@@ -287,7 +289,7 @@ pub fn Type(comptime model: Model) type {
         mem: Memory,
 
         // memory buffers
-        ram: [8][0x4000]u8, // up to 8 16-KByte RAM banks
+        ram: [8][0x4000]u8,
         rom: Rom,
         ext_buf: [EXP.BUF_SIZE]u8,
         fb: [DISPLAY.FB_SIZE]u8 align(128),
@@ -303,8 +305,20 @@ pub fn Type(comptime model: Model) type {
                     .junk_page = &self.junk_page,
                     .unmapped_page = &self.unmapped_page,
                 }),
-                // FIXME: on KC85/2, /3 fill with noise
-                .ram = std.mem.zeroes(@TypeOf(self.ram)),
+                .ram = init: {
+                    var arr: [8][0x4000]u8 = undefined;
+                    if (model == .KC854) {
+                        // on KC85/4, RAM is filled with zeroes
+                        arr = std.mem.zeroes(@TypeOf(self.ram));
+                    } else {
+                        // on KC85/2, /3 RAM is filled with noise
+                        var x: u32 = 0x6D98302B; // seed for xorshift32
+                        inline for (0..8) |i| {
+                            x = fillNoise(&arr[i], x);
+                        }
+                    }
+                    break :init arr;
+                },
                 .rom = initRoms(opts),
                 .ext_buf = std.mem.zeroes(@TypeOf(self.ext_buf)),
                 .fb = std.mem.zeroes(@TypeOf(self.fb)),
@@ -349,10 +363,6 @@ pub fn Type(comptime model: Model) type {
             };
         }
 
-        fn cp(src: []const u8, dst: []u8) void {
-            std.mem.copyForwards(u8, dst, src);
-        }
-
         fn initRoms(opts: Options) Rom {
             var rom: Rom = undefined;
             switch (model) {

src/systems/namco.zig

@@ -40,6 +40,7 @@ const memory = common.memory;
 const clock = common.clock;
 const filter = common.filter;
 const pin = common.bitutils.pin;
+const cp = common.utils.cp;
 const AudioCallback = common.glue.AudioCallback;
 const AudioOptions = common.glue.AudioOptions;
 const DisplayInfo = common.glue.DisplayInfo;
@@ -765,10 +766,6 @@ pub fn Type(comptime sys: System) type {
             }
         }
 
-        fn cp(src: []const u8, dst: []u8) void {
-            std.mem.copyForwards(u8, dst, src);
-        }
-
         fn initSysRom(opts: Options) [MEMMAP.CPU_ROM_SIZE]u8 {
             var rom: [MEMMAP.CPU_ROM_SIZE]u8 = undefined;
             if (sys == .Pacman) {