From 97101d7bc1369183d28305e85d357b45594ad3db Mon Sep 17 00:00:00 2001
From: Michel Heily <michelheily@gmail.com>
Date: Sat, 10 Oct 2020 10:57:00 -0700
Subject: [PATCH] core: dma: Delay DMA by 3 cycles

Former-commit-id: 06426b01a3e9e9084c97cd8f3a3de3b3c2b207e6
Former-commit-id: 2dee7bc2a2a3a3e69c7afa878f2d03208f330752
---
 core/src/dma.rs   | 30 +++++++++++++++++++-----------
 core/src/gba.rs   |  3 ++-
 core/src/sched.rs |  1 +
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/core/src/dma.rs b/core/src/dma.rs
index 4e61ed7..d8e1132 100644
--- a/core/src/dma.rs
+++ b/core/src/dma.rs
@@ -1,6 +1,7 @@
 use super::cartridge::BackupMedia;
 use super::interrupt::{self, Interrupt, InterruptConnect, SharedInterruptFlags};
 use super::iodev::consts::{REG_FIFO_A, REG_FIFO_B};
+use super::sched::{EventType, Scheduler, SharedScheduler};
 use super::sysbus::SysBus;
 use super::Bus;
 
@@ -20,8 +21,6 @@ pub struct DmaChannel {
     internal: DmaInternalRegs,
 
     running: bool,
-    cycles: usize,
-    start_cycles: usize,
     fifo_mode: bool,
     irq: Interrupt,
     interrupt_flags: SharedInterruptFlags,
@@ -47,8 +46,7 @@ impl DmaChannel {
             dst: 0,
             wc: 0,
             ctrl: DmaChannelCtrl(0),
-            cycles: 0,
-            start_cycles: 0,
+
             fifo_mode: false,
             internal: Default::default(),
             interrupt_flags,
@@ -98,7 +96,6 @@ impl DmaChannel {
                 self.dst,
                 self.wc
             );
-            self.start_cycles = self.cycles;
             self.running = true;
             start_immediately = timing == 0;
             self.internal.src_addr = self.src;
@@ -177,7 +174,6 @@ impl DmaChannel {
             interrupt::signal_irq(&self.interrupt_flags, self.irq);
         }
         if self.ctrl.repeat() {
-            self.start_cycles = self.cycles;
             /* reload */
             if 3 == self.ctrl.dst_adj() {
                 self.internal.dst_addr = self.dst;
@@ -193,7 +189,9 @@ impl DmaChannel {
 pub struct DmaController {
     pub channels: [DmaChannel; 4],
     pending_set: u8,
-    cycles: usize,
+    #[serde(skip)]
+    #[serde(default = "Scheduler::new_shared")]
+    scheduler: SharedScheduler,
 }
 
 impl InterruptConnect for DmaController {
@@ -205,7 +203,7 @@ impl InterruptConnect for DmaController {
 }
 
 impl DmaController {
-    pub fn new(interrupt_flags: SharedInterruptFlags) -> DmaController {
+    pub fn new(interrupt_flags: SharedInterruptFlags, scheduler: SharedScheduler) -> DmaController {
         DmaController {
             channels: [
                 DmaChannel::new(0, interrupt_flags.clone()),
@@ -214,7 +212,7 @@ impl DmaController {
                 DmaChannel::new(3, interrupt_flags.clone()),
             ],
             pending_set: 0,
-            cycles: 0,
+            scheduler: scheduler,
         }
     }
 
@@ -240,9 +238,11 @@ impl DmaController {
             8 => self.channels[channel_id].write_word_count(value),
             10 => {
                 if self.channels[channel_id].write_dma_ctrl(value) {
-                    self.pending_set |= 1 << channel_id;
+                    // DMA actually starts after 3 cycles
+                    self.scheduler
+                        .schedule(EventType::DmaActivateChannel(channel_id), 3);
                 } else {
-                    self.pending_set &= !(1 << channel_id);
+                    self.deactivate_channel(channel_id);
                 }
             }
             _ => panic!("Invalid dma offset {:x}", ofs),
@@ -268,6 +268,14 @@ impl DmaController {
             }
         }
     }
+
+    pub fn activate_channel(&mut self, channel_id: usize) {
+        self.pending_set |= 1 << channel_id;
+    }
+
+    pub fn deactivate_channel(&mut self, channel_id: usize) {
+        self.pending_set &= !(1 << channel_id);
+    }
 }
 
 pub const TIMING_VBLANK: u16 = 1;
diff --git a/core/src/gba.rs b/core/src/gba.rs
index 735498b..955eb19 100644
--- a/core/src/gba.rs
+++ b/core/src/gba.rs
@@ -77,7 +77,7 @@ impl GameBoyAdvance {
 
         let intc = InterruptController::new(interrupt_flags.clone());
         let gpu = Box::new(Gpu::new(scheduler.clone(), interrupt_flags.clone()));
-        let dmac = DmaController::new(interrupt_flags.clone());
+        let dmac = DmaController::new(interrupt_flags.clone(), scheduler.clone());
         let timers = Timers::new(interrupt_flags.clone());
         let sound_controller = Box::new(SoundController::new(
             scheduler.clone(),
@@ -329,6 +329,7 @@ impl EventHandler for GameBoyAdvance {
             &mut (*ptr).io as &mut IoDevices
         };
         match event {
+            EventType::DmaActivateChannel(channel_id) => io.dmac.activate_channel(channel_id),
             EventType::Gpu(event) => io.gpu.on_event(
                 event,
                 extra_cycles,
diff --git a/core/src/sched.rs b/core/src/sched.rs
index 4360bfe..ba69e37 100644
--- a/core/src/sched.rs
+++ b/core/src/sched.rs
@@ -29,6 +29,7 @@ pub enum ApuEvent {
 pub enum EventType {
     Gpu(GpuEvent),
     Apu(ApuEvent),
+    DmaActivateChannel(usize),
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone)]