linux/Documentation/hwmon/chipcap2.rst
Javier Carrasco 3af350929e hwmon: Add support for Amphenol ChipCap 2
The Amphenol ChipCap 2 is a capacitive polymer humidity and temperature
sensor with an integrated EEPROM and minimum/maximum humidity alarms.

All device variants offer an I2C interface and depending on the part
number, two different output modes:
- CC2D: digital output
- CC2A: analog (PDM) output

This driver adds support for the digital variant (CC2D part numbers),
which includes the following part numbers:
- non-sleep measurement mode (CC2D23, CC2D25, CC2D33, CC2D35)
- sleep measurement mode (CC2D23S, CC2D25S, CC2D33S, CC2D35S)

The Chipcap 2 EEPROM can be accessed to configure a series of parameters
like the minimum/maximum humidity alarm threshold and hysteresis. The
EEPROM is only accessible in the command window after a power-on reset.
The default window lasts 10 ms if no Start_CM command is sent. After the
command window is finished (either after the mentioned timeout of after
a Start_NOM command is sent), the device enters the normal operation
mode and makes a first measurement automatically.

Unfortunately, the device does not provide any hardware or software
reset and therefore the driver must trigger power cycles to enter the
command mode. A dedicated, external regulator is required for that.

This driver keeps the device off until a measurement or access to the
EEPROM is required, making use of the first automatic measurement to
avoid different code paths for sleep and non-sleep devices.

The minimum and maximum humidity alarms are configured with two
registers per alarm: one stores the alarm threshold and the other one
keeps the value that turns off the alarm. The alarm signals are only
updated when a measurement is carried out.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://lore.kernel.org/r/20240130-topic-chipcap2-v6-5-260bea05cf9b@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
2024-02-25 12:37:37 -08:00

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.. SPDX-License-Identifier: GPL-2.0-or-later
Kernel driver ChipCap2
======================
Supported chips:
* Amphenol CC2D23, CC2D23S, CC2D25, CC2D25S, CC2D33, CC2D33S, CC2D35, CC2D35S
Prefix: 'chipcap2'
Addresses scanned: -
Datasheet: https://www.amphenol-sensors.com/en/telaire/humidity/527-humidity-sensors/3095-chipcap-2
Author:
- Javier Carrasco <javier.carrasco.cruz@gmail.com>
Description
-----------
This driver implements support for the Amphenol ChipCap 2, a humidity and
temperature chip family. Temperature is measured in milli degrees celsius,
relative humidity is expressed as a per cent mille. The measurement ranges
are the following:
- Relative humidity: 0 to 100000 pcm (14-bit resolution)
- Temperature: -40000 to +125000 m°C (14-bit resolution)
The device communicates with the I2C protocol and uses the I2C address 0x28
by default.
Depending on the hardware configuration, up to two humidity alarms to control
minimum and maximum values are provided. Their thresholds and hystersis can be
configured via sysfs.
Thresholds and hysteris must be provided as a per cent mille. These values
might be truncated to match the 14-bit device resolution (6.1 pcm/LSB)
Known Issues
------------
The driver does not support I2C address and command window length modification.
sysfs-Interface
---------------
The following list includes the sysfs attributes that the driver always provides,
their permissions and a short description:
=============================== ======= ========================================
Name Perm Description
=============================== ======= ========================================
temp1_input: RO temperature input
humidity1_input: RO humidity input
=============================== ======= ========================================
The following list includes the sysfs attributes that the driver may provide
depending on the hardware configuration:
=============================== ======= ========================================
Name Perm Description
=============================== ======= ========================================
humidity1_min: RW humidity low limit. Measurements under
this limit trigger a humidity low alarm
humidity1_max: RW humidity high limit. Measurements above
this limit trigger a humidity high alarm
humidity1_min_hyst: RW humidity low hystersis
humidity1_max_hyst: RW humidity high hystersis
humidity1_min_alarm: RO humidity low alarm indicator
humidity1_max_alarm: RO humidity high alarm indicator
=============================== ======= ========================================