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Diffstat (limited to 'Documentation/w1/slaves/w1_therm.rst')
| -rw-r--r-- | Documentation/w1/slaves/w1_therm.rst | 50 |
1 files changed, 41 insertions, 9 deletions
diff --git a/Documentation/w1/slaves/w1_therm.rst b/Documentation/w1/slaves/w1_therm.rst index 90531c340a07..cc4edae17751 100644 --- a/Documentation/w1/slaves/w1_therm.rst +++ b/Documentation/w1/slaves/w1_therm.rst @@ -26,20 +26,31 @@ W1_THERM_DS1825 0x3B W1_THERM_DS28EA00 0x42 ==================== ==== -Support is provided through the sysfs w1_slave file. Each open and +Support is provided through the sysfs w1_slave file. Each open and read sequence will initiate a temperature conversion then provide two -lines of ASCII output. The first line contains the nine hex bytes +lines of ASCII output. The first line contains the nine hex bytes read along with a calculated crc value and YES or NO if it matched. -If the crc matched the returned values are retained. The second line +If the crc matched the returned values are retained. The second line displays the retained values along with a temperature in millidegrees Centigrade after t=. -Parasite powered devices are limited to one slave performing a -temperature conversion at a time. If none of the devices are parasite -powered it would be possible to convert all the devices at the same -time and then go back to read individual sensors. That isn't -currently supported. The driver also doesn't support reduced -precision (which would also reduce the conversion time) when reading values. +Alternatively, temperature can be read using temperature sysfs, it +return only temperature in millidegrees Centigrade. + +A bulk read of all devices on the bus could be done writing 'trigger' +in the therm_bulk_read sysfs entry at w1_bus_master level. This will +sent the convert command on all devices on the bus, and if parasite +powered devices are detected on the bus (and strong pullup is enable +in the module), it will drive the line high during the longer conversion +time required by parasited powered device on the line. Reading +therm_bulk_read will return 0 if no bulk conversion pending, +-1 if at least one sensor still in conversion, 1 if conversion is complete +but at least one sensor value has not been read yet. Result temperature is +then accessed by reading the temperature sysfs entry of each device, which +may return empty if conversion is still in progress. Note that if a bulk +read is sent but one sensor is not read immediately, the next access to +temperature on this device will return the temperature measured at the +time of issue of the bulk read command (not the current temperature). Writing a value between 9 and 12 to the sysfs w1_slave file will change the precision of the sensor for the next readings. This value is in (volatile) @@ -49,6 +60,27 @@ To store the current precision configuration into EEPROM, the value 0 has to be written to the sysfs w1_slave file. Since the EEPROM has a limited amount of writes (>50k), this command should be used wisely. +Alternatively, resolution can be set or read (value from 9 to 12) using the +dedicated resolution sysfs entry on each device. This sysfs entry is not +present for devices not supporting this feature. Driver will adjust the +correct conversion time for each device regarding to its resolution setting. +In particular, strong pullup will be applied if required during the conversion +duration. + +The write-only sysfs entry eeprom is an alternative for EEPROM operations: + * 'save': will save device RAM to EEPROM + * 'restore': will restore EEPROM data in device RAM. + +ext_power syfs entry allow tho check the power status of each device. + * '0': device parasite powered + * '1': device externally powered + +sysfs alarms allow read or write TH and TL (Temperature High an Low) alarms. +Values shall be space separated and in the device range (typical -55 degC +to 125 degC). Values are integer as they are store in a 8bit register in +the device. Lowest value is automatically put to TL.Once set, alarms could +be search at master level. + The module parameter strong_pullup can be set to 0 to disable the strong pullup, 1 to enable autodetection or 2 to force strong pullup. In case of autodetection, the driver will use the "READ POWER SUPPLY" |