1 files changed, 84 insertions, 0 deletions
diff --git a/src/pc80/mc146818rtc_early.c b/src/pc80/mc146818rtc_early.c
new file mode 100644
index 0000000000..1d268f0482
--- /dev/null
+++ b/src/pc80/mc146818rtc_early.c
@@ -0,0 +1,84 @@
+#include <pc80/mc146818rtc.h>
+#include <part/fallback_boot.h>
+
+static unsigned char cmos_read(unsigned char addr)
+{
+	outb(addr, RTC_BASE_PORT + 0);
+	return inb(RTC_BASE_PORT + 1);
+}
+
+static void cmos_write(unsigned char val, unsigned char addr)
+{
+	outb(addr, RTC_BASE_PORT + 0);
+	outb(val, RTC_BASE_PORT + 1);
+}
+
+static int cmos_error(void)
+{
+	unsigned char reg_d;
+	/* See if the cmos error condition has been flagged */
+	reg_d = cmos_read(RTC_REG_D);
+	return (reg_d & RTC_VRT) == 0;
+}
+
+static int cmos_chksum_valid(void)
+{
+	unsigned char addr;
+	unsigned long sum, old_sum;
+	sum = 0;
+	/* Comput the cmos checksum */
+	for(addr = LB_CKS_RANGE_START; addr <= LB_CKS_RANGE_END; addr++) {
+		sum += cmos_read(addr);
+	}
+	sum = (sum & 0xffff) ^ 0xffff;
+
+	/* Read the stored checksum */
+	old_sum = cmos_read(LB_CKS_LOC) << 8;
+	old_sum |=  cmos_read(LB_CKS_LOC+1);
+
+	return sum == old_sum;
+}
+
+
+static int do_normal_boot(void)
+{
+	unsigned char byte;
+
+	if (cmos_error() || !cmos_chksum_valid()) {
+		unsigned char byte;
+		/* There are no impossible values, no cheksums so just
+		 * trust whatever value we have in the the cmos,
+		 * but clear the fallback bit.
+		 */
+		byte = cmos_read(RTC_BOOT_BYTE);
+		byte &= 0x0c;
+		byte |= MAX_REBOOT_CNT << 4;
+		cmos_write(byte, RTC_BOOT_BYTE);
+	}
+
+	/* The RTC_BOOT_BYTE is now o.k. see where to go. */
+	byte = cmos_read(RTC_BOOT_BYTE);
+	
+	/* Are we in normal mode? */
+	if (byte & 1) {
+		byte &= 0x0f; /* yes, clear the boot count */
+	}
+
+	/* Are we already at the max count? */
+	if ((byte >> 4) < MAX_REBOOT_CNT) {
+		byte += 1 << 4; /* No, add 1 to the count */
+	}
+	else {
+		byte &= 0xfc;	/* Yes, put in fallback mode */
+	}
+
+	/* Is this the first boot? */
+	if ((byte >> 4) <= 1) {
+		byte = (byte & 0xfc) | ((byte & 1) << 1); /* yes, shift the boot bits */
+	}
+
+	/* Save the boot byte */
+	cmos_write(byte, RTC_BOOT_BYTE);
+
+	return ((byte >> 4) < MAX_REBOOT_CNT);
+}