feat(drivers): add VGA text-mode driver with scrolling and cursor

include/vga.h

@@ -0,0 +1,31 @@
+#ifndef FROSTBYTE_VGA_H
+#define FROSTBYTE_VGA_H
+
+#include "types.h"
+
+typedef enum {
+    vgaBlack = 0,
+    vgaBlue = 1,
+    vgaGreen = 2,
+    vgaCyan = 3,
+    vgaRed = 4,
+    vgaMagenta = 5,
+    vgaBrown = 6,
+    vgaLightGrey = 7,
+    vgaDarkGrey = 8,
+    vgaLightBlue = 9,
+    vgaLightGreen = 10,
+    vgaLightCyan = 11,
+    vgaLightRed = 12,
+    vgaPink = 13,
+    vgaYellow = 14,
+    vgaWhite = 15
+} VgaColor;
+
+void vgaInit(void);
+void vgaClear(void);
+void vgaPutChar(char c);
+void vgaWriteString(const char* str);
+void vgaSetColor(VgaColor foreground, VgaColor background);
+
+#endif

src/vga.c

@@ -0,0 +1,93 @@
+#include "vga.h"
+#include "ports.h"
+
+#define vgaWidth 80
+#define vgaHeight 25
+#define vgaBuffer 0xB8000
+
+static volatile uint16* const screen = (volatile uint16*)vgaBuffer;
+static uint32 cursorRow;
+static uint32 cursorColumn;
+static uint8 currentColor;
+
+static uint16 makeCell(char c, uint8 color)
+{
+    return (uint16)c | ((uint16)color << 8);
+}
+
+static void updateHardwareCursor(void)
+{
+    uint16 position = (uint16)(cursorRow * vgaWidth + cursorColumn);
+    outb(0x3D4, 0x0F);
+    outb(0x3D5, (uint8)(position & 0xFF));
+    outb(0x3D4, 0x0E);
+    outb(0x3D5, (uint8)((position >> 8) & 0xFF));
+}
+
+void vgaSetColor(VgaColor foreground, VgaColor background)
+{
+    currentColor = (uint8)foreground | (uint8)(background << 4);
+}
+
+void vgaClear(void)
+{
+    for (uint32 y = 0; y < vgaHeight; y++) {
+        for (uint32 x = 0; x < vgaWidth; x++)
+            screen[y * vgaWidth + x] = makeCell(' ', currentColor);
+    }
+    cursorRow = 0;
+    cursorColumn = 0;
+    updateHardwareCursor();
+}
+
+void vgaInit(void)
+{
+    currentColor = (uint8)vgaLightGrey | (uint8)(vgaBlack << 4);
+    vgaClear();
+}
+
+static void scroll(void)
+{
+    for (uint32 y = 1; y < vgaHeight; y++) {
+        for (uint32 x = 0; x < vgaWidth; x++)
+            screen[(y - 1) * vgaWidth + x] = screen[y * vgaWidth + x];
+    }
+    for (uint32 x = 0; x < vgaWidth; x++)
+        screen[(vgaHeight - 1) * vgaWidth + x] = makeCell(' ', currentColor);
+    cursorRow = vgaHeight - 1;
+}
+
+void vgaPutChar(char c)
+{
+    if (c == '\n') {
+        cursorColumn = 0;
+        cursorRow++;
+    } else if (c == '\r') {
+        cursorColumn = 0;
+    } else if (c == '\b') {
+        if (cursorColumn > 0) {
+            cursorColumn--;
+            screen[cursorRow * vgaWidth + cursorColumn] = makeCell(' ', currentColor);
+        }
+    } else if (c == '\t') {
+        cursorColumn = (cursorColumn + 4) & ~3u;
+    } else {
+        screen[cursorRow * vgaWidth + cursorColumn] = makeCell(c, currentColor);
+        cursorColumn++;
+    }
+
+    if (cursorColumn >= vgaWidth) {
+        cursorColumn = 0;
+        cursorRow++;
+    }
+    if (cursorRow >= vgaHeight)
+        scroll();
+
+    updateHardwareCursor();
+}
+
+void vgaWriteString(const char* str)
+{
+    while (*str)
+        vgaPutChar(*str++);
+}