1 files changed, 96 insertions, 0 deletions
diff --git a/kernel/con.c b/kernel/con.c
new file mode 100644
index 0000000..b3d2b9d
--- /dev/null
+++ b/kernel/con.c
@@ -0,0 +1,96 @@
+/*
+ * con.c
+ *
+ * Basic VGA text console
+ */
+
+#include <asm/io.h>
+#include <kernel/vsprintf.h>
+#include <stdarg.h>
+#include <stdint.h>
+
+#define COLS 80
+#define ROWS 25
+
+static uint8_t *vram = (uint8_t*) 0xB8000;
+static int pos;
+
+static inline void cursorpos(int pos) {
+	outb(0x3D4, 0x0E);
+	outb(0x3D5, (uint8_t) ((pos >> 9) & 0xFF));
+  outb(0x3D4, 0x0F);
+	outb(0x3D5, (uint8_t) ((pos >> 1) & 0xFF));
+}
+
+/* scrolls the console up one line */
+static void scroll_up(void) {
+  int n = (COLS * (ROWS - 1)) << 1;
+  uint8_t *p = vram;
+
+  while(n--) {
+    *p = p[COLS << 1];
+    p++;
+  }
+
+  p = (uint8_t*) (vram + (COLS * (ROWS - 1) << 1));
+  n = COLS;
+  while(n--) {
+    *p = ' ';
+    p += 2;
+  }
+
+  pos -= COLS << 1;
+  cursorpos(pos);
+}
+
+/* must be called before any console output */
+void con_init(void) {
+  int n = COLS * ROWS;
+  uint8_t *p = vram;
+
+  while(n--) {
+    *(p++) = 0x20;
+    *(p++) = 0x07;
+  }
+
+  pos = 0;
+  cursorpos(0);
+}
+
+/* write a zero-terminated string to console */
+void con_print(char *s) {
+  uint8_t *p = &vram[pos];
+
+  while(*s) {
+    if(*s == '\n') {
+      pos = (int) (p - vram);
+      pos = ((pos / (COLS << 1)) + 1) * (COLS << 1);
+      p = &vram[pos];
+      s++;
+    } else {
+      *p = *(s++);
+      p += 2;
+    }
+
+    pos = (int) (p - vram);
+
+    if(pos >= (COLS * ROWS) << 1)
+      scroll_up();
+  }
+
+  /* update the cursor position */
+  cursorpos(pos);
+}
+
+int printf(char *fmt, ...) {
+  int ret;
+  char buf[1024];
+  va_list ap;
+
+  va_start(ap, fmt);
+  ret = vsprintf(buf, fmt, ap);
+  va_end(ap);
+
+  con_print(buf);
+  return ret;
+}