Make use of the Century Bit to support years in the range from 1970 to
2169. Enable toggling of the bit at the end of a century on a clock
update.
---
The clock is used with the Broadcom SWARM and the D-Link DNS-323
platform.
I have verified correct operation with the SWARM -- the firmware assumes
19YY when CB is clear and 20YY otherwise. Which means years 1900-1969
will be shown as 2100-2169 in Linux. I think this is a feature rather
than a problem. The firmware does not set the CEB bit itself and does not
care of what its state is.
I will be happy to hear from a DNS-323 user to confirm or deny whether
such an interpretation is compatible.
Otherwise, please apply.
Maciej
patch-2.6.26-rc1-20080505-m41t80-century-4
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/drivers/rtc/rtc-m41t80.c linux-2.6.26-rc1-20080505/drivers/rtc/rtc-m41t80.c
--- linux-2.6.26-rc1-20080505.macro/drivers/rtc/rtc-m41t80.c 2008-05-05 02:55:40.000000000 +0000
+++ linux-2.6.26-rc1-20080505/drivers/rtc/rtc-m41t80.c 2008-05-16 21:16:48.000000000 +0000
@@ -52,6 +52,8 @@
(M41T80_REG_ALARM_SEC + 1 - M41T80_REG_ALARM_MON)
#define M41T80_SEC_ST (1 << 7) /* ST: Stop Bit */
+#define M41T80_HOUR_CEB (1 << 7) /* CEB: Century Enable Bit */
+#define M41T80_HOUR_CB (1 << 6) /* CB: Century Bit */
#define M41T80_ALMON_AFE (1 << 7) /* AFE: AF Enable Bit */
#define M41T80_ALMON_SQWE (1 << 6) /* SQWE: SQW Enable Bit */
#define M41T80_ALHOUR_HT (1 << 6) /* HT: Halt Update Bit */
@@ -164,8 +166,12 @@ static int m41t80_get_datetime(struct i2
tm->tm_wday = buf[M41T80_REG_WDAY] & 0x07;
tm->tm_mon = BCD2BIN(buf[M41T80_REG_MON] & 0x1f) - 1;
- /* assume 20YY not 19YY, and ignore the Century Bit */
- tm->tm_year = BCD2BIN(buf[M41T80_REG_YEAR]) + 100;
+ /* Assume 1970-2169, taking the Century Bit into account. */
+ tm->tm_year = BCD2BIN(buf[M41T80_REG_YEAR]);
+ if ((buf[M41T80_REG_HOUR] & M41T80_HOUR_CB) != 0)
+ tm->tm_year += 100;
+ if (tm->tm_year < 70)
+ tm->tm_year += 200;
return 0;
}
@@ -196,8 +202,14 @@ static int m41t80_set_datetime(struct i2
BIN2BCD(tm->tm_mday) | (buf[M41T80_REG_DAY] & ~0x3f);
buf[M41T80_REG_MON] =
BIN2BCD(tm->tm_mon + 1) | (buf[M41T80_REG_MON] & ~0x1f);
- /* assume 20YY not 19YY */
+ /* Assume 1970-2169 and set the Century Bit for 19YY/21YY. */
buf[M41T80_REG_YEAR] = BIN2BCD(tm->tm_year % 100);
+ if ((tm->tm_year / 100) % 2 != 0)
+ buf[M41T80_REG_HOUR] |= M41T80_HOUR_CB;
+ else
+ buf[M41T80_REG_HOUR] &= ~M41T80_HOUR_CB;
+ /* Enable toggling of the Century Bit at the end of a century. ;-) */
+ buf[M41T80_REG_HOUR] |= M41T80_HOUR_CEB;
if (m41t80_write_block_data(client, M41T80_REG_SSEC,
M41T80_DATETIME_REG_SIZE, buf) < 0) {
