1 files changed, 91 insertions, 0 deletions
diff --git a/os/boot/pc/cga.c b/os/boot/pc/cga.c
new file mode 100644
index 00000000..90e08aaf
--- /dev/null
+++ b/os/boot/pc/cga.c
@@ -0,0 +1,91 @@
+#include "u.h"
+#include "lib.h"
+#include "mem.h"
+#include "dat.h"
+#include "fns.h"
+
+enum {
+	Width		= 160,
+	Height		= 25,
+
+	Attr		= 7,		/* white on black */
+};
+
+#define CGASCREENBASE	((uchar*)KADDR(0xB8000))
+
+static int pos;
+static int screeninitdone;
+
+static uchar
+cgaregr(int index)
+{
+	outb(0x3D4, index);
+	return inb(0x3D4+1) & 0xFF;
+}
+
+static void
+cgaregw(int index, int data)
+{
+	outb(0x3D4, index);
+	outb(0x3D4+1, data);
+}
+
+static void
+movecursor(void)
+{
+	cgaregw(0x0E, (pos/2>>8) & 0xFF);
+	cgaregw(0x0F, pos/2 & 0xFF);
+	CGASCREENBASE[pos+1] = Attr;
+}
+
+static void
+cgascreenputc(int c)
+{
+	int i;
+
+	if(c == '\n'){
+		pos = pos/Width;
+		pos = (pos+1)*Width;
+	}
+	else if(c == '\t'){
+		i = 8 - ((pos/2)&7);
+		while(i-->0)
+			cgascreenputc(' ');
+	}
+	else if(c == '\b'){
+		if(pos >= 2)
+			pos -= 2;
+		cgascreenputc(' ');
+		pos -= 2;
+	}
+	else{
+		CGASCREENBASE[pos++] = c;
+		CGASCREENBASE[pos++] = Attr;
+	}
+	if(pos >= Width*Height){
+		memmove(CGASCREENBASE, &CGASCREENBASE[Width], Width*(Height-1));
+		memset(&CGASCREENBASE[Width*(Height-1)], 0, Width);
+		pos = Width*(Height-1);
+	}
+	movecursor();
+}
+
+static void
+screeninit(void)
+{
+	if(screeninitdone == 0){
+		pos = cgaregr(0x0E)<<8;
+		pos |= cgaregr(0x0F);
+		pos *= 2;
+		screeninitdone = 1;
+	}
+}
+
+void
+cgascreenputs(char* s, int n)
+{
+	if(screeninitdone == 0)
+		screeninit();
+	while(n-- > 0)
+		cgascreenputc(*s++);
+}