Kernel driver bt1-pvt¶
Supported chips:
Baikal-T1 PVT sensor (in SoC)
Prefix: 'bt1-pvt'
Addresses scanned: -
Datasheet: Provided by BAIKAL ELECTRONICS upon request and under NDA
- Authors:
Maxim Kaurkin <maxim.kaurkin@baikalelectronics.ru> Serge Semin <Sergey.Semin@baikalelectronics.ru>
Description¶
This driver implements support for the hardware monitoring capabilities of the embedded into Baikal-T1 process, voltage and temperature sensors. PVT IP-core consists of one temperature and four voltage sensors, which can be used to monitor the chip internal environment like heating, supply voltage and transistors performance. The driver can optionally provide the hwmon alarms for each sensor the PVT controller supports. The alarms functionality is made compile-time configurable due to the hardware interface implementation peculiarity, which is connected with an ability to convert data from only one sensor at a time. Additional limitation is that the controller performs the thresholds checking synchronously with the data conversion procedure. Due to these in order to have the hwmon alarms automatically detected the driver code must switch from one sensor to another, read converted data and manually check the threshold status bits. Depending on the measurements timeout settings (update_interval sysfs node value) this design may cause additional burden on the system performance. So in case if alarms are unnecessary in your system design it's recommended to have them disabled to prevent the PVT IRQs being periodically raised to get the data cache/alarms status up to date. By default in alarm-less configuration the data conversion is performed by the driver on demand when read operation is requested via corresponding _input-file.
Temperature Monitoring¶
Temperature is measured with 10-bit resolution and reported in millidegree Celsius. The driver performs all the scaling by itself therefore reports true temperatures that don't need any user-space adjustments. While the data translation formulae isn't linear, which gives us non-linear discreteness, it's close to one, but giving a bit better accuracy for higher temperatures. The temperature input is mapped as follows (the last column indicates the input ranges):
temp1: CPU embedded diode -48.38C - +147.438C
In case if the alarms kernel config is enabled in the driver the temperature input has associated min and max limits which trigger an alarm when crossed.
Voltage Monitoring¶
The voltage inputs are also sampled with 10-bit resolution and reported in millivolts. But in this case the data translation formulae is linear, which provides a constant measurements discreteness. The data scaling is also performed by the driver, so returning true millivolts. The voltage inputs are mapped as follows (the last column indicates the input ranges):
in0: VDD (processor core) 0.62V - 1.168V
in1: Low-Vt (low voltage threshold) 0.62V - 1.168V
in2: High-Vt (high voltage threshold) 0.62V - 1.168V
in3: Standard-Vt (standard voltage threshold) 0.62V - 1.168V
In case if the alarms config is enabled in the driver the voltage inputs have associated min and max limits which trigger an alarm when crossed.
Sysfs Attributes¶
Following is a list of all sysfs attributes that the driver provides, their permissions and a short description:
Name |
Perm |
Description |
---|---|---|
update_interval |
RW |
Measurements update interval per sensor. |
temp1_type |
RO |
Sensor type (always 1 as CPU embedded diode). |
temp1_label |
RO |
CPU Core Temperature sensor. |
temp1_input |
RO |
Measured temperature in millidegree Celsius. |
temp1_min |
RW |
Low limit for temp input. |
temp1_max |
RW |
High limit for temp input. |
temp1_min_alarm |
RO |
Temperature input alarm. Returns 1 if temperature input went below min limit, 0 otherwise. |
temp1_max_alarm |
RO |
Temperature input alarm. Returns 1 if temperature input went above max limit, 0 otherwise. |
temp1_offset |
RW |
Temperature offset in millidegree Celsius which is added to the temperature reading by the chip. It can be used to manually adjust the temperature measurements within 7.130 degrees Celsius. |
in[0-3]_label |
RO |
CPU Voltage sensor (either core or low/high/standard thresholds). |
in[0-3]_input |
RO |
Measured voltage in millivolts. |
in[0-3]_min |
RW |
Low limit for voltage input. |
in[0-3]_max |
RW |
High limit for voltage input. |
in[0-3]_min_alarm |
RO |
Voltage input alarm. Returns 1 if voltage input went below min limit, 0 otherwise. |
in[0-3]_max_alarm |
RO |
Voltage input alarm. Returns 1 if voltage input went above max limit, 0 otherwise. |