degree Celsius over a -10 to +85 degree range, a minimum/maximum alarm
default setting of 75 and 80 degrees respectively, and a maximum conversion
time of 750ms.
+
+In addition, the DS1721 supports four resolution settings from 9 to 12 bits
+(defined in degrees C per LSB: 0.5, 0.25, 0.125, and 0.0625, respectifully),
+that are set at device power on to the highest resolution: 12-bits (0.0625 degree C).
+
+Changing the DS1721 resolution mode affects the conversion time and can be
+done from userspace, via the device 'update_interval' sysfs attribute. This
+attribute will normalize range of input values to the device maximum resolution
+values defined in the datasheet as such:
+
+Resolution Conversion Time Input Range
+ (C/LSB) (msec) (msec)
+--------------------------------------------
+0.5 93.75 0....94
+0.25 187.5 95...187
+0.125 375 188..375
+0.0625 750 376..infinity
+--------------------------------------
+
+The following examples show how the 'update_interval' attribute can be
+used to change the conversion time:
+
+$ cat update_interval
+750
+$ cat temp1_input
+22062
+$
+$ echo 300 > update_interval
+$ cat update_interval
+375
+$ cat temp1_input
+22125
+$
+$ echo 150 > update_interval
+$ cat update_interval
+188
+$ cat temp1_input
+22250
+$
+$ echo 1 > update_interval
+$ cat update_interval
+94
+$ cat temp1_input
+22000
+$
+$ echo 1000 > update_interval
+$ cat update_interval
+750
+$ cat temp1_input
+22062
+$
+
+As shown, the ds1621 driver automatically adjusts the 'update_interval'
+user input, via a step function. Reading back the 'update_interval' value
+after a write operation provides the conversion time used by the device.
+
+Mathematically, the resolution can be derived from the conversion time
+via the following function:
+
+ g(x) = 0.5 * [minimum_conversion_time/x]
+
+where:
+ -> 'x' = the output from 'update_interval'
+ -> 'g(x)' = the resolution in degrees C per LSB.
+ -> 93.75ms = minimum conversion time
return sprintf(buf, "%d\n", !!(data->conf & attr->index));
}
+static ssize_t show_convrate(struct device *dev, struct device_attribute *da,
+ char *buf)
+{
+ struct i2c_client *client = to_i2c_client(dev);
+ struct ds1621_data *data = i2c_get_clientdata(client);
+ return scnprintf(buf, PAGE_SIZE, "%hu\n", data->update_interval);
+}
+
+static ssize_t set_convrate(struct device *dev, struct device_attribute *da,
+ const char *buf, size_t count)
+{
+ struct i2c_client *client = to_i2c_client(dev);
+ struct ds1621_data *data = i2c_get_clientdata(client);
+ unsigned long convrate;
+ s32 err;
+ int resol = 0;
+
+ err = kstrtoul(buf, 10, &convrate);
+ if (err)
+ return err;
+
+ /* Convert rate into resolution bits */
+ while (resol < (ARRAY_SIZE(ds1721_convrates) - 1) &&
+ convrate > ds1721_convrates[resol])
+ resol++;
+
+ mutex_lock(&data->update_lock);
+ data->conf = i2c_smbus_read_byte_data(client, DS1621_REG_CONF);
+ data->conf &= ~DS1621_REG_CONFIG_RESOL;
+ data->conf |= (resol << DS1621_REG_CONFIG_RESOL_SHIFT);
+ i2c_smbus_write_byte_data(client, DS1621_REG_CONF, data->conf);
+ data->update_interval = ds1721_convrates[resol];
+ mutex_unlock(&data->update_lock);
+
+ return count;
+}
+
static DEVICE_ATTR(alarms, S_IRUGO, show_alarms, NULL);
+static DEVICE_ATTR(update_interval, S_IWUSR | S_IRUGO, show_convrate,
+ set_convrate);
+
static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, show_temp, NULL, 0);
static SENSOR_DEVICE_ATTR(temp1_min, S_IWUSR | S_IRUGO, show_temp, set_temp, 1);
static SENSOR_DEVICE_ATTR(temp1_max, S_IWUSR | S_IRUGO, show_temp, set_temp, 2);
&sensor_dev_attr_temp1_min_alarm.dev_attr.attr,
&sensor_dev_attr_temp1_max_alarm.dev_attr.attr,
&dev_attr_alarms.attr,
+ &dev_attr_update_interval.attr,
NULL
};
+static umode_t ds1621_attribute_visible(struct kobject *kobj,
+ struct attribute *attr, int index)
+{
+ struct device *dev = container_of(kobj, struct device, kobj);
+ struct i2c_client *client = to_i2c_client(dev);
+ struct ds1621_data *data = i2c_get_clientdata(client);
+
+ if (attr == &dev_attr_update_interval.attr)
+ if (data->kind != ds1721)
+ /* shhh, we're hiding update_interval */
+ return 0;
+ return attr->mode;
+}
+
static const struct attribute_group ds1621_group = {
.attrs = ds1621_attributes,
+ .is_visible = ds1621_attribute_visible
};