From 4a66e1076005bf895295fb4270307f674b8f81fa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=A3o=20Magalh=C3=A3es?= <joamag@gmail.com>
Date: Sun, 25 Feb 2024 11:35:37 +0000
Subject: [PATCH] chore: better usage of const values
Improved some comments for DMA.
---
src/consts.rs | 8 ++++++++
src/dma.rs | 17 ++++++++++-------
src/mmu.rs | 18 ++++++++++++++----
3 files changed, 32 insertions(+), 11 deletions(-)
diff --git a/src/consts.rs b/src/consts.rs
index f9479564..8f083a1a 100644
--- a/src/consts.rs
+++ b/src/consts.rs
@@ -3,3 +3,11 @@ pub const DIV_ADDR: u16 = 0xff04;
pub const TIMA_ADDR: u16 = 0xff05;
pub const TMA_ADDR: u16 = 0xff06;
pub const TAC_ADDR: u16 = 0xff07;
+
+// DMA registers
+pub const DMA_ADDR: u16 = 0xff46;
+pub const HDMA1_ADDR: u16 = 0xff51;
+pub const HDMA2_ADDR: u16 = 0xff52;
+pub const HDMA3_ADDR: u16 = 0xff53;
+pub const HDMA4_ADDR: u16 = 0xff54;
+pub const HDMA5_ADDR: u16 = 0xff55;
diff --git a/src/dma.rs b/src/dma.rs
index a7cfb8a9..83261556 100644
--- a/src/dma.rs
+++ b/src/dma.rs
@@ -1,4 +1,7 @@
-use crate::warnln;
+use crate::{
+ consts::{HDMA1_ADDR, HDMA2_ADDR, HDMA3_ADDR, HDMA4_ADDR, HDMA5_ADDR},
+ warnln,
+};
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum DmaMode {
@@ -38,7 +41,7 @@ impl Dma {
pub fn read(&mut self, addr: u16) -> u8 {
match addr {
// 0xFF55 — HDMA5: VRAM DMA length/mode/start (CGB only)
- 0xff45 => ((self.length >> 4) - 1) as u8 | ((self.active as u8) << 7),
+ HDMA5_ADDR => ((self.length >> 4) - 1) as u8 | ((self.active as u8) << 7),
_ => {
warnln!("Reading from unknown DMA location 0x{:04x}", addr);
0xff
@@ -49,15 +52,15 @@ impl Dma {
pub fn write(&mut self, addr: u16, value: u8) {
match addr {
// 0xFF51 — HDMA1: VRAM DMA source high (CGB only)
- 0xff51 => self.source = (self.source & 0x00ff) | ((value as u16) << 8),
+ HDMA1_ADDR => self.source = (self.source & 0x00ff) | ((value as u16) << 8),
// 0xFF52 — HDMA2: VRAM DMA source low (CGB only)
- 0xff52 => self.source = (self.source & 0xff00) | ((value & 0xf0) as u16),
+ HDMA2_ADDR => self.source = (self.source & 0xff00) | ((value & 0xf0) as u16),
// 0xFF53 — HDMA3: VRAM DMA destination high (CGB only)
- 0xff53 => self.destination = (self.destination & 0x00ff) | ((value as u16) << 8),
+ HDMA3_ADDR => self.destination = (self.destination & 0x00ff) | ((value as u16) << 8),
// 0xFF54 — HDMA4: VRAM DMA destination low (CGB only)
- 0xff54 => self.destination = (self.destination & 0xff00) | ((value & 0xf0) as u16),
+ HDMA4_ADDR => self.destination = (self.destination & 0xff00) | ((value & 0xf0) as u16),
// 0xFF55 — HDMA5: VRAM DMA length/mode/start (CGB only)
- 0xff55 => {
+ HDMA5_ADDR => {
self.length = (((value & 0x7f) + 0x1) as u16) << 4;
self.mode = match (value & 80) >> 7 {
0 => DmaMode::General,
diff --git a/src/mmu.rs b/src/mmu.rs
index 757c4b96..082cba81 100644
--- a/src/mmu.rs
+++ b/src/mmu.rs
@@ -4,6 +4,7 @@ use std::sync::Mutex;
use crate::{
apu::Apu,
+ consts::DMA_ADDR,
debugln,
dma::Dma,
gb::{Components, GameBoyConfig, GameBoyMode, GameBoySpeed},
@@ -268,7 +269,16 @@ impl Mmu {
return;
}
- // @TODO: Implement DMA transfer in a better way
+ // @TODO: Implement DMA transfer in a better way, meaning that
+ // the DMA transfer should respect the timings
+
+ // In both Normal Speed and Double Speed Mode it takes about 8 μs
+ // to transfer a block of $10 bytes. That is, 8 M-cycles in Normal
+ // Speed Mode [1], and 16 “fast” M-cycles in Double Speed Mode [2].
+ // Older MBC controllers (like MBC1-3) and slower ROMs are not guaranteed
+ // to support General Purpose or HBlank DMA, that’s because there are
+ // always 2 bytes transferred per microsecond (even if the itself
+ // program runs it Normal Speed Mode).
// only runs the DMA transfer if the system is in CGB mode
// this avoids issues when writing to DMG unmapped registers
@@ -485,9 +495,9 @@ impl Mmu {
0x40 | 0x60 | 0x70 => {
match addr & 0x00ff {
// 0xFF46 — DMA: OAM DMA source address & start
- 0x0046 => {
- // @TODO must increment the cycle count by 160
- // and make this a separated dma.rs file
+ DMA_ADDR => {
+ // @TODO must update the data section only after 160 m cycles,
+ // making this an immediate operation creates issues
debugln!("Going to start DMA transfer to 0x{:x}00", value);
let data = self.read_many((value as u16) << 8, 160);
self.write_many(0xfe00, &data);
--
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