pcf2123 has an offset register, which can be used to make minor adjustments to the clock rate to compensate for temperature or a crystal that is not exactly right.
The adjustment is calculated in parts per billion. The data sheet uses parts per million (as do some others), but with 2 digits of precision. Since floating point is forbidden, parts per billion is a better fit. Add a pair of sysfs files to seetand retrieve the offset in ppm. Signed-off-by: Joshua Clayton <[email protected]> --- drivers/rtc/rtc-pcf2123.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 68 insertions(+) diff --git a/drivers/rtc/rtc-pcf2123.c b/drivers/rtc/rtc-pcf2123.c index d494638..6d70860 100644 --- a/drivers/rtc/rtc-pcf2123.c +++ b/drivers/rtc/rtc-pcf2123.c @@ -77,11 +77,17 @@ /* PCF2123_REG_SC BITS */ #define OSC_HAS_STOPPED (0x80) /* Clock has been stopped */ +/* PCF2123_REG_OFFSET BITS */ +#define OFFSET_COARSE (0x80) /* Coarse Mode Offset */ + /* READ/WRITE ADDRESS BITS */ #define PCF2123_SUBADDR (1 << 4) #define PCF2123_WRITE ((0 << 7) | PCF2123_SUBADDR) #define PCF2123_READ ((1 << 7) | PCF2123_SUBADDR) +/* offset granularity in parts per billion in fine mode */ +#define OFFSET_STEP (2170) + static struct spi_driver pcf2123_driver; /* @@ -166,6 +172,65 @@ static ssize_t pcf2123_store(struct device *dev, struct device_attribute *attr, return count; } +static ssize_t pcf2123_adjust_show(struct device *dev, + struct device_attribute *attr, char *buffer) +{ + ssize_t ret; + s8 reg; + + ret = pcf2123_read(dev, PCF2123_REG_OFFSET, ®, 1); + if (ret < 0) + return -EIO; + + if (reg & OFFSET_COARSE) { + reg <<= 1; + } else { + reg &= ~OFFSET_COARSE; + reg |= (reg & 0x40) << 1; /* sign extend */ + } + + return sprintf(buffer, "%ld\n", ((long)reg) * OFFSET_STEP); +} + +static ssize_t pcf2123_adjust_store(struct device *dev, + struct device_attribute *attr, + const char *buffer, size_t count) +{ + ssize_t ret; + long val; + s8 reg; + + ret = kstrtol(buffer, 10, &val); + if (ret) + return ret; + + if (val > OFFSET_STEP * 127) + reg = 127; + else if (val < OFFSET_STEP * -128) + reg = -128; + else + reg = (s8)((val + (OFFSET_STEP >> 1)) / OFFSET_STEP); + +/* + * Each even value of the fine adjust overlaps with a value of the coarse + * adjustment, and since the coarse adjsutment will spread the adjustments + * over both hours, we use coarse for all even values, as well as values + * that are beyond the range of fine adjustment + */ + if (reg <= 63 && reg >= -64 && reg & 1) { + reg &= ~OFFSET_COARSE; + } else { + reg >>= 1; + reg |= OFFSET_COARSE; + } + + pcf2123_write_reg(dev, PCF2123_REG_OFFSET, reg); + if (ret < 0) + return -EIO; + + return count; +} + static int pcf2123_rtc_read_time(struct device *dev, struct rtc_time *tm) { u8 rxbuf[7]; @@ -320,6 +385,8 @@ static DEVICE_ATTR(c, S_IRUGO | S_IWUSR, pcf2123_show, pcf2123_store); static DEVICE_ATTR(d, S_IRUGO | S_IWUSR, pcf2123_show, pcf2123_store); static DEVICE_ATTR(e, S_IRUGO | S_IWUSR, pcf2123_show, pcf2123_store); static DEVICE_ATTR(f, S_IRUGO | S_IWUSR, pcf2123_show, pcf2123_store); +static DEVICE_ATTR(adjust, S_IRUGO | S_IWUSR, pcf2123_adjust_show, + pcf2123_adjust_store); static struct attribute *pcf2123_attrs[] = { &dev_attr_0.attr, @@ -338,6 +405,7 @@ static struct attribute *pcf2123_attrs[] = { &dev_attr_d.attr, &dev_attr_e.attr, &dev_attr_f.attr, + &dev_attr_adjust.attr, NULL }; -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
