chore: clean up DMA code

src/Bus.zig

@@ -64,16 +64,7 @@ pub fn attach(self: *Self, cpu: *Arm7tdmi) void {
     self.cpu = cpu;
 }
 
-pub fn handleDMATransfers(self: *Self) void {
-    while (self.isDmaRunning()) {
-        if (self.dma[1].step(self)) continue;
-        if (self.dma[0].step(self)) continue;
-        if (self.dma[2].step(self)) continue;
-        if (self.dma[3].step(self)) continue;
-    }
-}
-
-inline fn isDmaRunning(self: *const Self) bool {
+pub inline fn isDmaRunning(self: *const Self) bool {
     return self.dma[0].active or
         self.dma[1].active or
         self.dma[2].active or

src/apu.zig

@@ -263,12 +263,12 @@ pub const Apu = struct {
 
         if (@boolToInt(self.dma_cnt.chA_timer.read()) == tim_id) {
             self.chA.updateSample();
-            if (self.chA.len() <= 15) cpu.bus.dma[1].enableSoundDma(0x0400_00A0);
+            if (self.chA.len() <= 15) cpu.bus.dma[1].requestSoundDma(0x0400_00A0);
         }
 
         if (@boolToInt(self.dma_cnt.chB_timer.read()) == tim_id) {
             self.chB.updateSample();
-            if (self.chB.len() <= 15) cpu.bus.dma[2].enableSoundDma(0x0400_00A4);
+            if (self.chB.len() <= 15) cpu.bus.dma[2].requestSoundDma(0x0400_00A4);
         }
     }
 

src/bus/dma.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 
 const DmaControl = @import("io.zig").DmaControl;
 const Bus = @import("../Bus.zig");
+const Arm7tdmi = @import("../cpu.zig").Arm7tdmi;
 
 pub const DmaTuple = std.meta.Tuple(&[_]type{ DmaController(0), DmaController(1), DmaController(2), DmaController(3) });
 const log = std.log.scoped(.DmaTransfer);
@@ -98,62 +99,35 @@ fn DmaController(comptime id: u2) type {
             self.writeCntHigh(@truncate(u16, word >> 16));
         }
 
-        pub fn step(self: *Self, bus: *Bus) bool {
+        pub fn step(self: *Self, cpu: *Arm7tdmi) bool {
             if (!self.active) return false;
 
-            const sad_adj = std.meta.intToEnum(Adjustment, self.cnt.sad_adj.read()) catch unreachable;
-            const dad_adj = std.meta.intToEnum(Adjustment, self.cnt.dad_adj.read()) catch unreachable;
             const is_fifo = (self.id == 1 or self.id == 2) and self.cnt.start_timing.read() == 0b11;
+            const sad_adj = Self.adjustment(self.cnt.sad_adj.read());
+            const dad_adj = if (is_fifo) .Fixed else Self.adjustment(self.cnt.dad_adj.read());
 
-            // // if (is_fifo) {
-            // //     const offset = @sizeOf(u32);
-            // //     bus.write(u32, self._dad, bus.read(u32, self._sad));
-
-            // //     // TODO: Deduplicate
-            // //     switch (sad_adj) {
-            // //         .Increment => self._sad +%= offset,
-            // //         .Decrement => self._sad -%= offset,
-            // //         .Fixed => {},
-
-            // //         // TODO: Figure out correct behaviour on Illegal Source Addr Control Type
-            // //         .IncrementReload => std.debug.panic("panic(DmaTransfer): {} is an illegal src addr adjustment type", .{sad_adj}),
-            // //     }
-
-            // //     self._fifo_word_count -= 1;
-
-            // //     if (self._fifo_word_count == 0) {
-            // //         self._fifo_word_count = 4;
-            // //         self.active = false;
-            // //     }
-
-            // //     return true;
-            // // }
-
-            const transfer_type = self.cnt.transfer_type.read() or is_fifo;
+            const transfer_type = is_fifo or self.cnt.transfer_type.read();
             const offset: u32 = if (transfer_type) @sizeOf(u32) else @sizeOf(u16);
 
             if (transfer_type) {
-                bus.write(u32, self._dad, bus.read(u32, self._sad));
+                cpu.bus.write(u32, self._dad, cpu.bus.read(u32, self._sad));
             } else {
-                bus.write(u16, self._dad, bus.read(u16, self._sad));
+                cpu.bus.write(u16, self._dad, cpu.bus.read(u16, self._sad));
             }
 
             switch (sad_adj) {
                 .Increment => self._sad +%= offset,
                 .Decrement => self._sad -%= offset,
+                // TODO: Is just ignoring this ok?
+                .IncrementReload => log.err("{} is a prohibited adjustment on SAD", .{sad_adj}),
                 .Fixed => {},
-
-                // TODO: Figure out correct behaviour on Illegal Source Addr Control Type
-                .IncrementReload => std.debug.panic("panic(DmaTransfer): {} is an illegal src addr adjustment type", .{sad_adj}),
             }
 
-            if (!is_fifo) {
             switch (dad_adj) {
                 .Increment, .IncrementReload => self._dad +%= offset,
                 .Decrement => self._dad -%= offset,
                 .Fixed => {},
             }
-            }
 
             self._word_count -= 1;
 
@@ -162,12 +136,15 @@ fn DmaController(comptime id: u2) type {
                     // If we're not repeating, Fire the IRQs and disable the DMA
                     if (self.cnt.irq.read()) {
                         switch (id) {
-                            0 => bus.io.irq.dma0.set(),
-                            1 => bus.io.irq.dma0.set(),
-                            2 => bus.io.irq.dma0.set(),
-                            3 => bus.io.irq.dma0.set(),
+                            0 => cpu.bus.io.irq.dma0.set(),
+                            1 => cpu.bus.io.irq.dma0.set(),
+                            2 => cpu.bus.io.irq.dma0.set(),
+                            3 => cpu.bus.io.irq.dma0.set(),
                         }
+
+                        cpu.handleInterrupt();
                     }
+
                     self.cnt.enabled.unset();
                 }
 
@@ -196,21 +173,28 @@ fn DmaController(comptime id: u2) type {
 
             if (self.cnt.repeat.read() and self.active) {
                 self._word_count = if (self.word_count == 0) std.math.maxInt(@TypeOf(self._word_count)) else self.word_count;
-
-                const dad_adj = std.meta.intToEnum(Adjustment, self.cnt.dad_adj.read()) catch unreachable;
-                if (dad_adj == .IncrementReload) self._dad = self.dad;
+                if (Self.adjustment(self.cnt.dad_adj.read()) == .IncrementReload) self._dad = self.dad;
             }
         }
 
-        pub fn enableSoundDma(self: *Self, fifo_addr: u32) void {
+        pub fn requestSoundDma(self: *Self, fifo_addr: u32) void {
             comptime std.debug.assert(id == 1 or id == 2);
 
-            if (self.cnt.enabled.read() and self.cnt.start_timing.read() == 0b11 and self.dad == fifo_addr) {
-                self.active = true;
+            const is_enabled = self.cnt.enabled.read();
+            const is_special = self.cnt.start_timing.read() == 0b11;
+            const is_repeating = self.cnt.repeat.read();
+            const is_fifo = self.dad == fifo_addr;
+
+            if (is_enabled and is_special and is_repeating and is_fifo) {
                 self._word_count = 4;
-                self.cnt.repeat.set();
+                self.cnt.transfer_type.set();
+                self.active = true;
             }
         }
+
+        fn adjustment(idx: u2) Adjustment {
+            return std.meta.intToEnum(Adjustment, idx) catch unreachable;
+        }
     };
 }
 

src/cpu.zig

@@ -267,6 +267,15 @@ pub const Arm7tdmi = struct {
         }
     }
 
+    pub fn handleDMATransfers(self: *Self) void {
+        while (self.bus.isDmaRunning()) {
+            if (self.bus.dma[1].step(self)) continue;
+            if (self.bus.dma[0].step(self)) continue;
+            if (self.bus.dma[2].step(self)) continue;
+            if (self.bus.dma[3].step(self)) continue;
+        }
+    }
+
     pub fn handleInterrupt(self: *Self) void {
         const should_handle = self.bus.io.ie.raw & self.bus.io.irq.raw;
 

src/emu.zig

@@ -48,7 +48,7 @@ pub fn runFrame(sched: *Scheduler, cpu: *Arm7tdmi) void {
     while (sched.tick < frame_end) {
         if (cpu.bus.io.haltcnt == .Halt) sched.tick += 1;
         if (cpu.bus.io.haltcnt == .Execute) cpu.step();
-        cpu.bus.handleDMATransfers();
+        cpu.handleDMATransfers();
 
         while (sched.tick >= sched.nextTimestamp()) {
             sched.handleEvent(cpu);