From 93d331bb078c75b7ab030c4a6509306c3a4e9cd0 Mon Sep 17 00:00:00 2001
From: Ry <ryanst755@gmail.com>
Date: Sat, 12 Mar 2022 13:12:10 -0800
Subject: [PATCH] fox32+fox32rom: Use DMA for the disk controller

Instead of accessing one byte at a time, use a DMA-like system to
read/write a whole sector at a time directly to/from memory.
---
 src/bus.rs  | 22 ++++++++--------------
 src/disk.rs | 14 ++++++++------
 2 files changed, 16 insertions(+), 20 deletions(-)

diff --git a/src/bus.rs b/src/bus.rs
index 9c38b63..a842165 100644
--- a/src/bus.rs
+++ b/src/bus.rs
@@ -88,11 +88,8 @@ impl Bus {
                         }
                     }
                     0x20 => {
-                        // we're reading from the sector buffer
-                        if address_or_id > 512 {
-                            panic!("attempted to read past the end of the disk controller sector buffer");
-                        }
-                        self.disk_controller.sector_buffer[address_or_id] as u32
+                        // we're getting the location of the memory sector buffer
+                        self.disk_controller.buffer_pointer as u32
                     }
                     _ => panic!("invalid disk controller port"),
                 }
@@ -174,27 +171,24 @@ impl Bus {
                         };
                     }
                     0x20 => {
-                        // we're writing to the sector buffer
-                        if address_or_id > 512 {
-                            panic!("attempted to read past the end of the disk controller sector buffer");
-                        }
-                        self.disk_controller.sector_buffer[address_or_id] = word as u8;
+                        // we're setting the location of the memory sector buffer
+                        self.disk_controller.buffer_pointer = word as usize;
                     }
                     0x30 => {
-                        // we're reading the specified sector of the specified disk id into the sector buffer
+                        // we're reading the specified sector of the specified disk id into the memory sector buffer
                         if address_or_id > 3 {
                             panic!("invalid disk ID");
                         }
                         self.disk_controller.set_current_sector(address_or_id as u8, word);
-                        self.disk_controller.read_into_buffer(address_or_id as u8);
+                        self.disk_controller.read_into_memory(address_or_id as u8, self.memory.ram());
                     }
                     0x40 => {
-                        // we're writing the specified sector to the specified disk id from the sector buffer
+                        // we're writing the specified sector to the specified disk id from the memory sector buffer
                         if address_or_id > 3 {
                             panic!("invalid disk ID");
                         }
                         self.disk_controller.set_current_sector(address_or_id as u8, word);
-                        self.disk_controller.write_from_buffer(address_or_id as u8);
+                        self.disk_controller.write_from_memory(address_or_id as u8, self.memory.ram());
                     }
                     _ => panic!("invalid disk controller port"),
                 }
diff --git a/src/disk.rs b/src/disk.rs
index 291d2e7..ed0228b 100644
--- a/src/disk.rs
+++ b/src/disk.rs
@@ -1,5 +1,7 @@
 // disk.rs
 
+use crate::memory::MemoryRam;
+
 use std::fs::File;
 use std::io::{Seek, SeekFrom, Read, Write};
 use rfd::FileDialog;
@@ -22,14 +24,14 @@ impl Disk {
 
 pub struct DiskController {
     pub disk: [Option<Disk>; 4],
-    pub sector_buffer: [u8; 512],
+    pub buffer_pointer: usize,
 }
 
 impl DiskController {
     pub fn new() -> Self {
         DiskController {
             disk: [None, None, None, None],
-            sector_buffer: [0; 512]
+            buffer_pointer: 0x00000000
         }
     }
     pub fn select_file(&self) -> Option<File> {
@@ -64,18 +66,18 @@ impl DiskController {
         let disk = self.disk[disk_id as usize].as_mut().expect("attempted to access unmounted disk");
         disk.current_sector
     }
-    pub fn read_into_buffer(&mut self, disk_id: u8) -> usize {
+    pub fn read_into_memory(&mut self, disk_id: u8, ram: &mut MemoryRam) -> usize {
         let disk = self.disk[disk_id as usize].as_mut().expect("attempted to access unmounted disk");
         let mut temp_buffer = [0u8; 512];
 
         let number_of_bytes_read = disk.file.read(&mut temp_buffer).unwrap();
-        self.sector_buffer = temp_buffer;
+        ram[self.buffer_pointer..self.buffer_pointer+512].copy_from_slice(&temp_buffer);
         number_of_bytes_read
     }
-    pub fn write_from_buffer(&mut self, disk_id: u8) -> usize {
+    pub fn write_from_memory(&mut self, disk_id: u8, ram: &MemoryRam) -> usize {
         let disk = self.disk[disk_id as usize].as_mut().expect("attempted to access unmounted disk");
 
-        let number_of_bytes_written = disk.file.write(&mut self.sector_buffer).unwrap();
+        let number_of_bytes_written = disk.file.write(ram.get(self.buffer_pointer..self.buffer_pointer+512).unwrap()).unwrap();
         number_of_bytes_written
     }
 }
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