Kernel: Add terminal scrolling

kernel/arch/i386/tty.c

@@ -6,6 +6,7 @@
 #include <kernel/tty.h>
 
 #include "vga.h"
+#include "../../kernel/asm_helper.h" // FIXME
 
 static const size_t VGA_WIDTH = 80;
 static const size_t VGA_HEIGHT = 25;
@@ -38,14 +39,42 @@ void terminal_putentryat(unsigned char c, uint8_t color, size_t x, size_t y) {
 	terminal_buffer[index] = vga_entry(c, color);
 }
 
+// Updates the hardware cursor.
+static void move_cursor()
+{
+   // The screen is 80 characters wide...
+   uint16_t cursorLocation = terminal_row * 80 + terminal_column;
+   outb(0x3D4, 14);                  // Tell the VGA board we are setting the high cursor byte.
+   outb(0x3D5, cursorLocation >> 8); // Send the high cursor byte.
+   outb(0x3D4, 15);                  // Tell the VGA board we are setting the low cursor byte.
+   outb(0x3D5, cursorLocation);      // Send the low cursor byte.
+}
+
 void terminal_scroll(int line) {
-	int loop;
-	int c;
- 
-	for(loop = line * (VGA_WIDTH * 2) + 0xB8000; loop < VGA_WIDTH * 2; loop++) {
-		c = loop;
-		//*(loop - (VGA_WIDTH * 2)) = c;
-	}
+	// Get a space character with the default colour attributes.
+	int attributeByte = (0 /*black*/ << 4) | (15 /*white*/ & 0x0F);
+	uint16_t blank = 0x20 /* space */ | (attributeByte << 8);
+
+        // Row 25 is the end, this means we need to scroll up
+        if(terminal_row >= 25)
+        {
+            // Move the current text chunk that makes up the screen
+            // back in the buffer by a line
+            int i;
+            for (i = 0*80; i < 24*80; i++)
+            {
+                terminal_buffer[i] = terminal_buffer[i+80];
+            }
+     
+            // The last line should now be blank. Do this by writing
+            // 80 spaces to it.
+            for (i = 24*80; i < 25*80; i++)
+            {
+                terminal_buffer[i] = blank;
+            }
+            // The cursor should now be on the last line.
+            terminal_row = 24;
+        }
 }
 
  
@@ -65,18 +94,19 @@ void terminal_putchar(char c) {
 	  if (++terminal_column == VGA_WIDTH) {
 	    terminal_column = 0;
 	    if (++terminal_row == VGA_HEIGHT) {
-	      for(int line = 1; line <= VGA_HEIGHT - 1; line++)
-			{
-				terminal_scroll(line);
-			}
-			terminal_delete_last_line();
-			terminal_row = VGA_HEIGHT - 1;
+             	for(int line = 1; line <= VGA_HEIGHT - 1; line++) {
+			terminal_scroll(line);
+		}
+        	terminal_delete_last_line();
+		terminal_row = VGA_HEIGHT - 1;
 	    }
 	  }
 	} else {
 	  terminal_row += 1;
 	  terminal_column = 0;
 	}
+	terminal_scroll(terminal_row);
+	move_cursor();
 }
 
 void terminal_write(const char* data, size_t size) {