From 268961262ddee506c554515792fa9716497a6b89 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sat, 29 Oct 2022 01:30:12 -0300
Subject: [PATCH] feat(dma): implement all dma i/o reads

---
 src/core/bus/dma.zig | 29 ++++++++++++++++++++++++-----
 src/core/ppu.zig     |  8 +-------
 src/util.zig         | 11 +++++++++--
 3 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/src/core/bus/dma.zig b/src/core/bus/dma.zig
index a0404df..97b86d7 100644
--- a/src/core/bus/dma.zig
+++ b/src/core/bus/dma.zig
@@ -10,6 +10,7 @@ const log = std.log.scoped(.DmaTransfer);
 
 const setHi = util.setHi;
 const setLo = util.setLo;
+const shift = util.shift;
 
 const rotr = @import("../../util.zig").rotr;
 
@@ -22,20 +23,38 @@ pub fn read(comptime T: type, dma: *const DmaTuple, addr: u32) ?T {
 
     return switch (T) {
         u32 => switch (byte) {
-            0xB8 => @as(T, dma.*[0].cnt.raw) << 16,
-            0xC4 => @as(T, dma.*[1].cnt.raw) << 16,
-            0xD0 => @as(T, dma.*[2].cnt.raw) << 16,
-            0xDC => @as(T, dma.*[3].cnt.raw) << 16,
+            0xB0, 0xB4 => null, // DMA0SAD, DMA0DAD,
+            0xB8 => @as(T, dma.*[0].cnt.raw) << 16, // DMA0CNT_L is write-only
+            0xBC, 0xC0 => null, // DMA1SAD, DMA1DAD
+            0xC4 => @as(T, dma.*[1].cnt.raw) << 16, // DMA1CNT_L is write-only
+            0xC8, 0xCC => null, // DMA2SAD, DMA2DAD
+            0xD0 => @as(T, dma.*[2].cnt.raw) << 16, // DMA2CNT_L is write-only
+            0xD4, 0xD8 => null, // DMA3SAD, DMA3DAD
+            0xDC => @as(T, dma.*[3].cnt.raw) << 16, // DMA3CNT_L is write-only
             else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         },
         u16 => switch (byte) {
+            0xB0...0xB8 => null, // DMA0SAD, DMA0DAD, DMA0CNT_L
             0xBA => dma.*[0].cnt.raw,
+            0xBC...0xC4 => null, // DMA1SAD, DMA1DAD, DMA1CNT_L
             0xC6 => dma.*[1].cnt.raw,
+            0xC8...0xD0 => null, // DMA2SAD, DMA2DAD, DMA2CNT_L
             0xD2 => dma.*[2].cnt.raw,
+            0xD4...0xDC => null, // DMA3SAD, DMA3DAD, DMA3CNT_L
             0xDE => dma.*[3].cnt.raw,
             else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         },
-        u8 => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+        u8 => switch (byte) {
+            0xB0...0xB9 => null, // DMA0SAD, DMA0DAD, DMA0CNT_L
+            0xBA...0xBB => @truncate(T, dma.*[0].cnt.raw >> shift(byte)),
+            0xBC...0xC5 => null, // DMA1SAD, DMA1DAD, DMA1CNT_L
+            0xC6...0xC7 => @truncate(T, dma.*[1].cnt.raw >> shift(byte)),
+            0xC8...0xD1 => null, // DMA2SAD, DMA2DAD, DMA2CNT_L
+            0xD2...0xD3 => @truncate(T, dma.*[2].cnt.raw >> shift(byte)),
+            0xD4...0xDD => null, // DMA3SAD, DMA3DAD, DMA3CNT_L
+            0xDE...0xDF => @truncate(T, dma.*[3].cnt.raw >> shift(byte)),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+        },
         else => @compileError("DMA: Unsupported read width"),
     };
 }
diff --git a/src/core/ppu.zig b/src/core/ppu.zig
index 1dfef6a..d9a3f4a 100644
--- a/src/core/ppu.zig
+++ b/src/core/ppu.zig
@@ -13,6 +13,7 @@ const log = std.log.scoped(.PPU);
 
 const setHi = util.setHi;
 const setLo = util.setLo;
+const shift = util.shift;
 const pollDmaOnBlank = @import("bus/dma.zig").pollDmaOnBlank;
 
 pub const width = 240;
@@ -81,13 +82,6 @@ pub fn read(comptime T: type, ppu: *const Ppu, addr: u32) ?T {
     };
 }
 
-/// Calculates the correct shift offset for an aligned/unaligned u8 read
-///
-/// TODO: Rename this
-inline fn shift(byte: u8) u4 {
-    return @truncate(u4, byte & 1) << 3;
-}
-
 pub fn write(comptime T: type, ppu: *Ppu, addr: u32, value: T) void {
     const byte = @truncate(u8, addr); // prefixed with 0x0400_00
 
diff --git a/src/util.zig b/src/util.zig
index 4dc1c52..4d73bb3 100644
--- a/src/util.zig
+++ b/src/util.zig
@@ -12,9 +12,9 @@ pub fn sext(comptime T: type, comptime U: type, value: T) T {
 
     const iT = std.meta.Int(.signed, @typeInfo(T).Int.bits);
     const ExtU = if (@typeInfo(U).Int.signedness == .unsigned) T else iT;
-    const shift = @intCast(Log2Int(T), @typeInfo(T).Int.bits - @typeInfo(U).Int.bits);
+    const shift_amt = @intCast(Log2Int(T), @typeInfo(T).Int.bits - @typeInfo(U).Int.bits);
 
-    return @bitCast(T, @bitCast(iT, @as(ExtU, @truncate(U, value)) << shift) >> shift);
+    return @bitCast(T, @bitCast(iT, @as(ExtU, @truncate(U, value)) << shift_amt) >> shift_amt);
 }
 
 /// See https://godbolt.org/z/W3en9Eche
@@ -276,6 +276,13 @@ pub const audio = struct {
     };
 };
 
+/// Calculates the correct shift offset for an aligned/unaligned u8 read
+///
+/// TODO: Rename this
+pub inline fn shift(byte: u8) u4 {
+    return @truncate(u4, byte & 1) << 3;
+}
+
 /// Sets the high bits of an integer to a value
 pub inline fn setLo(comptime T: type, left: T, right: HalfInt(T)) T {
     return switch (T) {