[U-Boot-Users] [PATCH] Add support for M41T60 serial access real-time clock

[U-Boot-Users] [PATCH] Add support for M41T60 serial access real-time clock

[Lawrence R. Johnson]

Hi everyone,

Here is a patch to add support to U-Boot for the STMicroelectronics M41T60 serial RTC.  I used the driver for the M41T11 as a template.

The code was tested using an AMCC Sequoia board (PPC440EPx processor) with the M41T60 connected to the board's I2C0 header.

In the intended application, the RTC will be powered by a large capacitor, rather than a battery.  The driver therefore checks to see whether the RTC has lost power.  The chip's OUT bit is normally reset from its power-up state.  If the OUT bit is read as set, or if the date and time are not valid, then the RTC is assumed to have lost power, and its date and time are reset to 1900-01-01 00:00:00.

Signed-off-by: Larry Johnson <lrj@acm.org>

diff -Naur a/rtc/m41t60.c b/rtc/m41t60.c
--- a/rtc/m41t60.c	1969-12-31 19:00:00.000000000 -0500
+++ b/rtc/m41t60.c	2007-06-18 11:02:11.000000000 -0400
@@ -0,0 +1,234 @@
+/*
+ * (C) Copyright 2007
+ * Larry Johnson, lrj at acm.org
+ *
+ * based on rtc/m41t11.c which is ...
+ *
+ * (C) Copyright 2002
+ * Andrew May, Viasat Inc, amay at viasat.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+/*
+ * STMicroelectronics M41T60 serial access real-time clock
+ */
+
+/* #define DEBUG 1 */
+
+#include <common.h>
+#include <command.h>
+#include <rtc.h>
+#include <i2c.h>
+
+#if defined(CONFIG_RTC_M41T60) && defined(CFG_I2C_RTC_ADDR) && \
+	(CONFIG_COMMANDS & CFG_CMD_DATE)
+
+static unsigned bcd2bin(uchar n)
+{
+	return ((((n >> 4) & 0x0F) * 10) + (n & 0x0F));
+}
+
+static unsigned char bin2bcd(unsigned int n)
+{
+	return (((n / 10) << 4) | (n % 10));
+}
+
+/*
+	Convert between century and "century bits" (CB1 and CB0).  These
+	routines assume years are in the range 1900 - 2299.
+*/
+
+static unsigned char year2cb(unsigned const year)
+{
+	if (year < 1900 || year >= 2300) {
+		printf("M41T60 RTC: year %d out of range\n", year);
+	}
+	return (year / 100) & 0x3;
+}
+
+static unsigned cb2year(unsigned const cb)
+{
+	return 1900 + 100 * ((cb + 1) & 0x3);
+}
+
+/*
+ * These are simple defines for the chip local to here so they aren't too
+ * verbose.  DAY/DATE aren't nice but that is how they are on the data sheet.
+ */
+#define RTC_SEC		0x0
+#define RTC_MIN		0x1
+#define RTC_HOUR	0x2
+#define RTC_DAY		0x3
+#define RTC_DATE	0x4
+#define RTC_MONTH	0x5
+#define RTC_YEARS	0x6
+
+#define RTC_REG_CNT	7
+
+#define RTC_CTRL	0x7
+
+#if defined(DEBUG)
+static void rtc_dump(char const *const label)
+{
+	uchar data[8];
+
+	if (i2c_read(CFG_I2C_RTC_ADDR, 0, 1, data, sizeof(data))) {
+		printf("I2C read failed in rtc_dump()\n");
+		return;
+	}
+	printf("RTC dump %s: %02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X\n",
+	       label, data[0], data[1], data[2], data[3],
+	       data[4], data[5], data[6], data[7]);
+}
+#else				/* !defined(DEBUG) */
+#define rtc_dump(label)
+#endif /* defined(DEBUG) */
+
+static uchar *rtc_validate(void)
+{
+	static const uchar daysInMonth[0x13] = {
+		0x00, 0x31, 0x29, 0x31, 0x30, 0x31, 0x30, 0x31,
+		0x31, 0x30, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x31, 0x30, 0x31
+	};
+	static uchar data[8];
+	uchar min, date, month, years;
+
+	rtc_dump("begin validate");
+	if (i2c_read(CFG_I2C_RTC_ADDR, 0, 1, data, sizeof(data))) {
+		printf("I2C read failed in rtc_validate()\n");
+		return 0;
+	}
+	/*
+	 * If the OUT bit is "1", there has been a loss of power, then stop the
+	 * oscillator is it will be "kick-started".
+	 */
+	if (0x00 != (data[RTC_CTRL] & 0x80)) {
+		printf("M41T60 RTC clock lost power.\n");
+		data[RTC_SEC] = 0x80;
+		if (i2c_write(CFG_I2C_RTC_ADDR, RTC_SEC, 1, data, 1)) {
+			printf("I2C write failed in rtc_validate()\n");
+			return 0;
+		}
+	}
+	/*
+	 * If the ocsillator is stopped or the date is invalid, then set the OUT
+	 * bit to "1", reset the date registers, and start the oscillator.
+	 */
+	min = data[RTC_MIN] & 0x7F;
+	date = data[RTC_DATE];
+	month = data[RTC_MONTH] & 0x3F;
+	years = data[RTC_YEARS];
+	if (0x59 < data[RTC_SEC] || 0x09 < (data[RTC_SEC] & 0x0F) ||
+	    0x59 < min || 0x09 < (min & 0x0F) ||
+	    0x23 < data[RTC_HOUR] || 0x09 < (data[RTC_HOUR] & 0x0F) ||
+	    0x07 < data[RTC_DAY] || 0x00 == data[RTC_DAY] ||
+	    0x12 < month ||
+	    0x99 < years || 0x09 < (years & 0x0F) ||
+	    daysInMonth[month] < date || 0x09 < (date & 0x0F) || 0x00 == date ||
+	    (0x29 == date && 0x02 == month &&
+	     ((0x00 != (years & 0x03)) ||
+	      (0x00 == years && 0x00 != (data[RTC_MONTH] & 0xC0))))) {
+		printf("Resetting M41T60 RTC clock.\n");
+		/*
+		 * Set to 00:00:00 1900-01-01 (Monday)
+		 */
+		data[RTC_SEC] = 0x00;
+		data[RTC_MIN] = 0x00;
+		data[RTC_HOUR] = 0x00;
+		data[RTC_DAY] = 0x02;
+		data[RTC_DATE] = 0x01;
+		data[RTC_MONTH] = 0xC1;
+		data[RTC_YEARS] = 0x00;
+		data[RTC_CTRL] &= 0x7F;
+	}
+	if (i2c_write(CFG_I2C_RTC_ADDR, 0, 1, data, sizeof(data))) {
+		printf("I2C write failed in rtc_validate()\n");
+		return 0;
+	}
+	return data;
+}
+
+void rtc_get(struct rtc_time *tmp)
+{
+	uchar const *const data = rtc_validate();
+
+	if (!data) {
+		return;
+	}
+	tmp->tm_sec = bcd2bin(data[RTC_SEC] & 0x7F);
+	tmp->tm_min = bcd2bin(data[RTC_MIN] & 0x7F);
+	tmp->tm_hour = bcd2bin(data[RTC_HOUR] & 0x3F);
+	tmp->tm_mday = bcd2bin(data[RTC_DATE] & 0x3F);
+	tmp->tm_mon = bcd2bin(data[RTC_MONTH] & 0x1F);
+	tmp->tm_year = cb2year(data[RTC_MONTH] >> 6) + bcd2bin(data[RTC_YEARS]);
+	tmp->tm_wday = bcd2bin(data[RTC_DAY] & 0x07) - 1;
+	tmp->tm_yday = 0;
+	tmp->tm_isdst = 0;
+
+	debug("Get DATE: %4d-%02d-%02d (wday=%d)  TIME: %2d:%02d:%02d\n",
+	      tmp->tm_year, tmp->tm_mon, tmp->tm_mday, tmp->tm_wday,
+	      tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
+}
+
+void rtc_set(struct rtc_time *tmp)
+{
+	uchar *const data = rtc_validate();
+
+	if (!data) {
+		return;
+	}
+	data[RTC_SEC] &= 0x80;
+	data[RTC_MIN] &= 0X80;
+
+	debug("Set DATE: %4d-%02d-%02d (wday=%d)  TIME: %2d:%02d:%02d\n",
+	      tmp->tm_year, tmp->tm_mon, tmp->tm_mday, tmp->tm_wday,
+	      tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
+
+	data[RTC_SEC] |= bin2bcd(tmp->tm_sec) & 0x7F;
+	data[RTC_MIN] |= bin2bcd(tmp->tm_min) & 0X7F;
+	data[RTC_HOUR] = bin2bcd(tmp->tm_hour) & 0x3F;
+	data[RTC_DATE] = bin2bcd(tmp->tm_mday) & 0x3F;
+	data[RTC_MONTH] = bin2bcd(tmp->tm_mon) & 0x1F;
+	data[RTC_YEARS] = bin2bcd(tmp->tm_year % 100);
+	data[RTC_MONTH] |= year2cb(tmp->tm_year) << 6;
+	data[RTC_DAY] = bin2bcd(tmp->tm_wday + 1) & 0x07;
+	if (i2c_write(CFG_I2C_RTC_ADDR, 0, 1, data, RTC_REG_CNT)) {
+		printf("I2C write failed in rtc_set()\n");
+		return;
+	}
+}
+
+void rtc_reset(void)
+{
+	uchar *const data = rtc_validate();
+
+	if (!data) {
+		return;
+	}
+	rtc_dump("begin reset");
+	/*
+	 * Turn off frequency test.
+	 */
+	data[RTC_CTRL] &= 0xBF;
+	if (i2c_write(CFG_I2C_RTC_ADDR, RTC_CTRL, 1, data + RTC_CTRL, 1)) {
+		printf("I2C write failed in rtc_reset()\n");
+		return;
+	}
+	rtc_dump("end reset");
+}
+#endif /* CONFIG_RTC_M41T60 && CFG_I2C_RTC_ADDR && CFG_CMD_DATE */
diff -Naur a/rtc/Makefile b/rtc/Makefile
--- a/rtc/Makefile	2007-06-12 08:23:00.000000000 -0400
+++ b/rtc/Makefile	2007-06-16 11:46:11.000000000 -0400
@@ -31,7 +31,8 @@
 	  bf5xx_rtc.o ds12887.o ds1302.o ds1306.o ds1307.o \
 	  ds1337.o ds1374.o ds1556.o ds164x.o ds174x.o ds3231.o \
 	  m41t11.o max6900.o m48t35ax.o mc146818.o mk48t59.o \
-	  mpc5xxx.o mpc8xx.o pcf8563.o s3c24x0_rtc.o rs5c372.o
+	  mpc5xxx.o mpc8xx.o pcf8563.o s3c24x0_rtc.o rs5c372.o \
+	  m41t60.o
 
 SRCS	:= $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS))

[U-Boot-Users] [PATCH] Add support for M41T60 serial access real-time clock

[Andrew Dyer]

On 6/18/07, Lawrence R. Johnson <lrj@arlinx.com> wrote:
> Hi everyone,
>
> Here is a patch to add support to U-Boot for the STMicroelectronics M41T60 serial RTC.  I used the driver for the M41T11 as a template.
>

We also use this chip.  A few comments below:

> The code was tested using an AMCC Sequoia board (PPC440EPx processor) with the M41T60 connected to the board's I2C0 header.
>
> In the intended application, the RTC will be powered by a large capacitor, rather than a battery.  The driver therefore checks to see whether the RTC has lost power.  The chip's OUT bit is normally reset from its power-up state.  If the OUT bit is read as set, or if the date and time are not valid, then the RTC is assumed to have lost power, and its date and time are reset to 1900-01-01 00:00:00.
>
> Signed-off-by: Larry Johnson <lrj@acm.org>
>
> diff -Naur a/rtc/m41t60.c b/rtc/m41t60.c
> --- a/rtc/m41t60.c      1969-12-31 19:00:00.000000000 -0500
> +++ b/rtc/m41t60.c      2007-06-18 11:02:11.000000000 -0400

> +/*
> +       Convert between century and "century bits" (CB1 and CB0).  These
> +       routines assume years are in the range 1900 - 2299.
> +*/
> +
> +static unsigned char year2cb(unsigned const year)
> +{
> +       if (year < 1900 || year >= 2300) {
> +               printf("M41T60 RTC: year %d out of range\n", year);
> +       }
> +       return (year / 100) & 0x3;
> +}

This doesn't match the defined mapping in the datasheet between the
century bits and years which has '00' corresponding to 2000.

> +
> +static unsigned cb2year(unsigned const cb)
> +{
> +       return 1900 + 100 * ((cb + 1) & 0x3);
> +}
> +
> +/*
> + * These are simple defines for the chip local to here so they aren't too
> + * verbose.  DAY/DATE aren't nice but that is how they are on the data sheet.
> + */
> +#define RTC_SEC                0x0
> +#define RTC_MIN                0x1
> +#define RTC_HOUR       0x2
> +#define RTC_DAY                0x3
> +#define RTC_DATE       0x4
> +#define RTC_MONTH      0x5
> +#define RTC_YEARS      0x6
> +
> +#define RTC_REG_CNT    7
> +
> +#define RTC_CTRL       0x7
> +
> +#if defined(DEBUG)
> +static void rtc_dump(char const *const label)
> +{
> +       uchar data[8];
> +
> +       if (i2c_read(CFG_I2C_RTC_ADDR, 0, 1, data, sizeof(data))) {
> +               printf("I2C read failed in rtc_dump()\n");
> +               return;
> +       }
> +       printf("RTC dump %s: %02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X\n",
> +              label, data[0], data[1], data[2], data[3],
> +              data[4], data[5], data[6], data[7]);
> +}
> +#else                          /* !defined(DEBUG) */
> +#define rtc_dump(label)
> +#endif /* defined(DEBUG) */

I would suggest to use the u-boot debug() macro here

> +       if (0x00 != (data[RTC_CTRL] & 0x80)) {

couldn't this be written as
if(data[RTC_CTRL] & 0x80)

> +       /*
> +        * If the ocsillator is stopped or the date is invalid, then set the OUT
> +        * bit to "1", reset the date registers, and start the oscillator.
> +        */
> +       min = data[RTC_MIN] & 0x7F;
> +       date = data[RTC_DATE];
> +       month = data[RTC_MONTH] & 0x3F;
> +       years = data[RTC_YEARS];
> +       if (0x59 < data[RTC_SEC] || 0x09 < (data[RTC_SEC] & 0x0F) ||
> +           0x59 < min || 0x09 < (min & 0x0F) ||
> +           0x23 < data[RTC_HOUR] || 0x09 < (data[RTC_HOUR] & 0x0F) ||
> +           0x07 < data[RTC_DAY] || 0x00 == data[RTC_DAY] ||
> +           0x12 < month ||
> +           0x99 < years || 0x09 < (years & 0x0F) ||
> +           daysInMonth[month] < date || 0x09 < (date & 0x0F) || 0x00 == date ||
> +           (0x29 == date && 0x02 == month &&
> +            ((0x00 != (years & 0x03)) ||
> +             (0x00 == years && 0x00 != (data[RTC_MONTH] & 0xC0))))) {
> +               printf("Resetting M41T60 RTC clock.\n");
> +               /*
> +                * Set to 00:00:00 1900-01-01 (Monday)
> +                */
> +               data[RTC_SEC] = 0x00;
> +               data[RTC_MIN] = 0x00;
> +               data[RTC_HOUR] = 0x00;
> +               data[RTC_DAY] = 0x02;
> +               data[RTC_DATE] = 0x01;
> +               data[RTC_MONTH] = 0xC1;
> +               data[RTC_YEARS] = 0x00;
> +               data[RTC_CTRL] &= 0x7F;

here you are resetting the calibration bits.  It would be nice to have
the option to try to fetch the calibration bits from the u-boot
environment and restore them.  Also your code is clearing the FT and
OUT/OFIE bits, which someone might be using for something.  This
behaviour should at least be noted in the comments.  Better would be
an option as to how to handle those bits on reset.


-- 
Hardware, n.:
        The parts of a computer system that can be kicked.

[U-Boot-Users] [PATCH] Add support for M41T60 serial access real-time clock

[Lawrence R. Johnson]

Andrew Dyer wrote:
> On 6/18/07, Lawrence R. Johnson <lrj@arlinx.com> wrote:
>> Hi everyone,
>>
>> Here is a patch to add support to U-Boot for the STMicroelectronics
>> M41T60 serial RTC.  I used the driver for the M41T11 as a template.
>>
> 
> We also use this chip.  A few comments below:

Hi Andrew (and list).  I'm glad to here you are also using the chip.  Thank you for you comments.

[...]
>> +/*
>> +       Convert between century and "century bits" (CB1 and CB0).  These
>> +       routines assume years are in the range 1900 - 2299.
>> +*/
>> +
>> +static unsigned char year2cb(unsigned const year)
>> +{
>> +       if (year < 1900 || year >= 2300) {
>> +               printf("M41T60 RTC: year %d out of range\n", year);
>> +       }
>> +       return (year / 100) & 0x3;
>> +}
> 
> This doesn't match the defined mapping in the datasheet between the
> century bits and years which has '00' corresponding to 2000.

I believe this code does return "00" when "year" is 2000.  As an added test, I've confirmed that 28 February 2000 rolls over to 29 February, whereas 28 February 1900, 2100, and 2200 all roll over to 1 March.

[...] 

>> +#if defined(DEBUG)
>> +static void rtc_dump(char const *const label)
>> +{
>> +       uchar data[8];
>> +
>> +       if (i2c_read(CFG_I2C_RTC_ADDR, 0, 1, data, sizeof(data))) {
>> +               printf("I2C read failed in rtc_dump()\n");
>> +               return;
>> +       }
>> +       printf("RTC dump %s: %02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X\n",
>> +              label, data[0], data[1], data[2], data[3],
>> +              data[4], data[5], data[6], data[7]);
>> +}
>> +#else                          /* !defined(DEBUG) */
>> +#define rtc_dump(label)
>> +#endif /* defined(DEBUG) */
> 
> I would suggest to use the u-boot debug() macro here

As far as I can determine, the debug() macro only provides a conditionally-compiled printf statement.  In some cases, it would still be necessary to define an array and perform the i2c_read, which would also need to be conditionally compiled.  I put the code into a static function to avoid duplicating code and cluttering the non-debug code with #ifdef's.

> 
>> +       if (0x00 != (data[RTC_CTRL] & 0x80)) {
> 
> couldn't this be written as
> if(data[RTC_CTRL] & 0x80)
> 

Yes, and I'd expect the compiler to generate the same object code either way.  The way I wrote it is more in keeping with the coding style I'm used to, but I don't have an objection to changing it if others prefer it the other way.

>> +       /*
>> +        * If the ocsillator is stopped or the date is invalid, then
>> set the OUT
>> +        * bit to "1", reset the date registers, and start the
>> oscillator.
>> +        */

Oops, this comment is wrong (and misspelled).  It should read:
+	/*
+	 * If the oscillator is stopped or the date is invalid, then reset the
+	 * OUT bit to "0", reset the date registers, and start the oscillator.
+	 */

>> +       min = data[RTC_MIN] & 0x7F;
>> +       date = data[RTC_DATE];
>> +       month = data[RTC_MONTH] & 0x3F;
>> +       years = data[RTC_YEARS];
>> +       if (0x59 < data[RTC_SEC] || 0x09 < (data[RTC_SEC] & 0x0F) ||
>> +           0x59 < min || 0x09 < (min & 0x0F) ||
>> +           0x23 < data[RTC_HOUR] || 0x09 < (data[RTC_HOUR] & 0x0F) ||
>> +           0x07 < data[RTC_DAY] || 0x00 == data[RTC_DAY] ||
>> +           0x12 < month ||
>> +           0x99 < years || 0x09 < (years & 0x0F) ||
>> +           daysInMonth[month] < date || 0x09 < (date & 0x0F) || 0x00
>> == date ||
>> +           (0x29 == date && 0x02 == month &&
>> +            ((0x00 != (years & 0x03)) ||
>> +             (0x00 == years && 0x00 != (data[RTC_MONTH] & 0xC0))))) {
>> +               printf("Resetting M41T60 RTC clock.\n");
>> +               /*
>> +                * Set to 00:00:00 1900-01-01 (Monday)
>> +                */
>> +               data[RTC_SEC] = 0x00;
>> +               data[RTC_MIN] = 0x00;
>> +               data[RTC_HOUR] = 0x00;
>> +               data[RTC_DAY] = 0x02;
>> +               data[RTC_DATE] = 0x01;
>> +               data[RTC_MONTH] = 0xC1;
>> +               data[RTC_YEARS] = 0x00;
>> +               data[RTC_CTRL] &= 0x7F;
> 
> here you are resetting the calibration bits.  It would be nice to have
> the option to try to fetch the calibration bits from the u-boot
> environment and restore them.  Also your code is clearing the FT and
> OUT/OFIE bits, which someone might be using for something.  This
> behaviour should at least be noted in the comments.  Better would be
> an option as to how to handle those bits on reset.
> 

This code is executed when it appears that the chip has lost (and regained) power.  In that case, the FT and OFIE bits are documented to come up reset to "0", so they are not changed.  The calibration bits also appear to all come up as "0", though I didn't find any mention of this in the data sheet.  I do use the OUT bit to detect power loss, as noted in the comments in the code.  If someone wanted to use the OUT bit for some other purpose, the driver would need to be modified, perhaps with a conditional compilation.

I like the idea of using an environmental variable to hold the RTC calibration, as this chip has no on-board EEPROM.  Can anyone tell me if there is such a variable defined now?  If not, is there a way to have one assigned?  Can the current patch be applied to the code base now, and the support for calibration bits added as an enhancement?  I'd appreciate any direction the list can give me.

-- Larry