Testing performance with different write modes

src/colors.rs

@@ -41,6 +41,12 @@ pub enum Color16Bit {
     White = 0xF,
 }
 
+impl From<Color16Bit> for u8 {
+    fn from(value: Color16Bit) -> u8 {
+        value as u8
+    }
+}
+
 /// Represents a color for vga text modes.
 #[derive(Debug, Copy, Clone)]
 #[repr(transparent)]

src/vga.rs

@@ -1,7 +1,7 @@
 //! Provides access to the vga graphics card.
 
 use super::{
-    colors::PALETTE_SIZE,
+    colors::{Color16Bit, PALETTE_SIZE},
     configurations::{
         VgaConfiguration, MODE_40X25_CONFIGURATION, MODE_40X50_CONFIGURATION,
         MODE_640X480X16_CONFIGURATION, MODE_80X25_CONFIGURATION,
@@ -89,6 +89,8 @@ impl From<ReadPlane> for u8 {
 bitflags! {
     /// Represents the plane masks of the `SequencerIndex::PlaneMask` register.
     pub struct PlaneMask: u8 {
+        /// Represents none of the plane masks of vga memory.
+        const NONE = 0b0000_0000;
         /// Represents `Plane0` of vga memory.
         const PLANE0 = 0b0000_0001;
         /// Represents `Plane1` of vga memory.
@@ -97,7 +99,7 @@ bitflags! {
         const PLANE2 = 0b0000_0100;
         /// Represents `Plane3` of vga memory.
         const PLANE3 = 0b0000_1000;
-        /// Represents a combination of all the plane masks.
+        /// Represents all of the plane masks of vga memory.
         const ALL_PLANES = Self::PLANE0.bits() | Self::PLANE1.bits() | Self::PLANE2.bits() | Self::PLANE3.bits();
     }
 }
@@ -351,6 +353,32 @@ impl Vga {
             .write(GraphicsControllerIndex::ReadPlaneSelect, read_plane);
     }
 
+    /// Sets the value to use for `GraphicsControllerIndex::SetReset`,
+    /// as spcified by `color`.
+    pub fn set_graphics_set_reset(&mut self, color: Color16Bit) {
+        let original_value = self
+            .graphics_controller_registers
+            .read(GraphicsControllerIndex::SetReset)
+            & 0xF0;
+        self.graphics_controller_registers.write(
+            GraphicsControllerIndex::SetReset,
+            original_value | u8::from(color),
+        );
+    }
+
+    /// Sets which planes are effected by `GraphicsControllerIndex::SetReset`,
+    /// as specified by `plane_mask`.
+    pub fn set_graphics_enable_set_reset(&mut self, plane_mask: PlaneMask) {
+        let original_value = self
+            .graphics_controller_registers
+            .read(GraphicsControllerIndex::EnableSetReset)
+            & 0xF0;
+        self.graphics_controller_registers.write(
+            GraphicsControllerIndex::EnableSetReset,
+            original_value | u8::from(plane_mask),
+        );
+    }
+
     fn set_registers(&mut self, configuration: &VgaConfiguration) {
         let emulation_mode = self.get_emulation_mode();
 

src/writers/graphics_640x480x16.rs

@@ -2,7 +2,6 @@ use crate::{
     colors::{Color16Bit, DEFAULT_PALETTE},
     vga::{PlaneMask, Vga, VideoMode, VGA},
 };
-use core::convert::TryInto;
 use spinning_top::SpinlockGuard;
 
 const WIDTH: usize = 640;
@@ -36,6 +35,7 @@ impl Graphics640x480x16 {
     pub fn clear_screen(&self) {
         let (mut vga, frame_buffer) = self.get_frame_buffer();
         vga.set_plane_mask(PlaneMask::ALL_PLANES);
+        vga.set_graphics_enable_set_reset(PlaneMask::NONE);
         for offset in 0..ALL_PLANES_SCREEN_SIZE {
             unsafe {
                 frame_buffer
@@ -50,24 +50,20 @@ impl Graphics640x480x16 {
         let (mut vga, frame_buffer) = self.get_frame_buffer();
         let offset = x / 8 + (WIDTH / 8) * y;
 
-        // Store the current value for masking.
-        let x = x & 7;
-        let mask = 0x80 >> (x & 7);
-        let mut plane_mask = 0x01;
+        // Write to all 4 planes
+        vga.set_plane_mask(PlaneMask::ALL_PLANES);
 
-        for plane in 0u8..4u8 {
-            vga.set_read_plane(plane.try_into().unwrap());
-            vga.set_plane_mask(plane.try_into().unwrap());
-            let current_value = unsafe { frame_buffer.add(offset).read_volatile() };
-            let new_value = if plane_mask & color as u8 != 0 {
-                current_value | mask
-            } else {
-                current_value & !mask
-            };
+        // Set the bits we want set/reset to the color
+        vga.set_graphics_set_reset(color);
+
+        // Enable set/reset for all planes
+        vga.set_graphics_enable_set_reset(PlaneMask::ALL_PLANES);
         unsafe {
-                frame_buffer.add(offset).write_volatile(new_value);
-            }
-            plane_mask <<= 1;
+            // In write mode 0, when enable set/reset is turned on, cpu data
+            // is replaced with the data from the set/reset register. Since
+            // we're using set/reset for all 4 planes, it doesn't matter what value
+            // we write to the memory address.
+            frame_buffer.add(offset).write(0x0);
         }
     }