add time.c

boot/Makefile

@@ -5,7 +5,7 @@ PROG = boot
 SRCS = srt0.S gdt.S boot.c
 OBJS = srt0.o gdt.o boot.o
 
-ESRCS = console.c print.c a20.c
+ESRCS = console.c print.c a20.c time.c
 OBJS += $(ESRCS:.c=.o)
 
 include $(SDIR)/Makefile.inc

boot/fn.h

@@ -11,6 +11,9 @@ void print(const char *fmt, ...);
 // a20.c
 void a20up(void);
 
+// long.c
+long getsecs(void);
+
 static __inline void
 outb(int port, u8 data)
 {

boot/time.c

@@ -0,0 +1,67 @@
+#include <u.h>
+#include "dat.h"
+#include "fn.h"
+
+// https://stanislavs.org/helppc/int_1a.html
+#define INT_TIME 2<<8
+#define INT_DATE 4<<8
+
+static int
+bcd2int(u8 c)
+{
+	return ((c & 0xf0)/8*5+(c & 0x0f));	
+}
+
+static int
+isleap(int y)
+{
+	return ((y % 4 == 0 && y % 100) || (y % 400 == 0));
+}
+
+static long 
+date2day(int y, u8 m, u8 d)
+{
+	long t;	
+	static const u16 m2d[] = {(u16)-1,
+		0,31,59,90,120,151,181,212,243,273,304,334,365};
+
+	t = (y - 1970) * 365 + m2d[m] + d - 1;
+	y -= (m <= 2);
+	for(; y >= 1970; --y){
+		if(isleap(y))
+			t += 1;
+	}
+	return t;
+}
+
+// bios long data
+static void 
+int1a(int f, u8 *b)
+{
+	__asm volatile("int $0x3a \n\t"
+		"setc %b0\n\t"
+		"movb %%ch, 0(%2)\n\t"
+		"movb %%cl, 1(%2)\n\t"
+		"movb %%dh, 2(%2)\n\t"
+		"movb %%dl, 3(%2)\n\t"
+		: "=a" (f)
+		: "0" (f), "r" (b)
+		: "%ecx", "%edx", "cc");
+	b[0] = bcd2int(b[0]);
+	b[1] = bcd2int(b[1]);
+	b[2] = bcd2int(b[2]);
+	b[3] = bcd2int(b[3]);
+}
+
+long
+getsecs(void)
+{
+	u8 t[4], d[4];
+	long s;
+
+	int1a(INT_TIME, t);
+	int1a(INT_DATE, d);
+	s = (date2day(d[0]*100+d[1], d[2], d[3]) * 24 + t[0]) * 60
+		+ (t[1] * 60) + t[2];
+	return s;	
+}