adapt Sensors doc

doc/Sensors.md

@@ -1,6 +1,6 @@
 Sensors
 =======
-The software contains support for a couple of sensors (starting from [20231228](../../releases/tag/20231228) and extend in consecutive releases).
+The software contains support for a couple of sensors (starting from [20231228](../../releases/tag/20231228) and extended in consecutive releases).
 This includes some I2C Sensors and SSI rotary encoders.
 To connect sensors the following steps are necessary:
 
@@ -29,9 +29,56 @@ Bus Usage
 ---------
 When selecting sensors to be connected at the M5 grove ports in the [online build service](BuildService.md) the system will select the appropriate bus (i2c-1, i2c-2) by it's own. As you can have up to 4 grove ports (one at the device and 3 by using the [M5 Atomic PortABC](https://shop.m5stack.com/products/atomic-portabc-extension-base)) you can use both available i2c buses (and still utilize other groves for serial or CAN).
 
+Implementing Own Sensors
+---------------------
+To add an own sensor implementation you typically need to handle the following parts:
+* (opt) add a library that supports your sensor
+* add some [XDR Mapping](./XdrMappings.md) that will convert your generated NMEA2000 message into an NMEA0183 XDR record and ensure the display on the data page
+* implement the sensor initialization
+* implement the measurement and generating the NMEA2000 message
+
+You typically would do this in a [user task](../lib/exampletask/Readme.md).<br>
+You can either just implement everything by your own or reuse the existing infrastructure for sensors.
+
+OwnImplementation
+__________________
+
+To implement everything by your own just create a config.json for the parameters you need, add an XDR mapping in a task init function (see e.g. [PressureXdr](../lib/iictask/GwIicSensors.h#L27)).
+In your user taks just initialize the sensor using your config values and add a loop that periodically measures the sensor value and sends out an nmea2000 message (using the [api->sendN2KMessage](../lib/api/GwApi.h#L137)).
+To display some information on the status page just add a countergroup in your task init function ([api->addCounter](../lib/api/GwApi.h#L170)) and increment a counter of this group on every measure ([api->increment](../lib/api/GwApi.h#L171)).
+To utilize a bus you typically would need to add the related library to your environment and add some bus initialization to define the pins that are used for this particular bus.
+Be carefull if you additionally would like to use sensors from the core as the core potentially would already initialize some bus - depending on the compile flags you provide.
+If you need additional libraries for your sensor just add a platformio.ini to your usertask and define an environment that contains the additional libraries.
+If you would like to compile also other environments (i.e. without the additional libraries) you should wrap all the code that references the additional libraries with some #ifdef and add a define to your environment (see the implementations of the [sensors in the core](../lib/iictask/)).
+
+Using the core infrastructure
+_____________________________
+For sensors of bus types that are already supported by the core (mainly I2C) you can simplify your implementation.
+Just also start with a [usertask](../lib/exampletask/Readme.md). But you only need the task init function, a config.json and potentially a platformio.ini.
+In your task code just implement a class that handles the sensor - it should inherit from [SensorBase](../lib/sensors/GwSensor.h#L20) or from [IICSensorBase](../lib/iictask/GwIicSensors.h#L16).<br>
+You need to implement:
+* _readConfig_ - just read your configuration and fill attributes of your class. Especially set the "ok" to true and fill the interval field to define your measure interval.
+* _preinit_ - check if your snesor is configured ,add necessary XDR mappings and return true if your sensor is active. Do __not__ yet initialize the sensor hardware.
+* _isActive_ - return true if your sensor is active
+* _initDevice_ - init your sensor hardware and return true if this was ok
+* _measure_ - read the sensor data, send NMEA2000 messages and increment 
+counters
+
+The busType and busId fields of your imnplementation have to be set correctly.
+
+All the internal sensors are implemented using this approach - e.g. [BME280](../lib/iictask/GwBME280.cpp#L23).<br>
+Do not get confused by all the different defines and the special config handling - this is only there to be as generic as possible - typically not necessary for your own sensor implementation.
+
+To use an IIC bus you need to compile with flags that define the pins to be used for the IIC bus:
+* busId 1 (IIC bus 1): GWIIC_SDA, GWIIC_SCL
+* busId 2 (IIC bus 2): GWIIC_SDA2, GWIIC_SCL2
+
+So you would need to add such definitions to your environment in your platformio.ini.
+
 Implemented Sensors
 -------------------
-* [BME280](https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme280-ds002.pdf): temperature/humidity/pressure [PGNs: 130314,130312, 130313]
+* [BME280](https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme280-ds002.pdf): temperature/humidity/pressure [PGNs: 130314,130312, 130313, 130311 since 202412xx ]
+* [BMP280](https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bmp280-ds001.pdf) [since 202412xx]: temperature/pressure [PGNs: 130314,130312, 130311]
 * [QMP6988](https://m5stack.oss-cn-shenzhen.aliyuncs.com/resource/docs/datasheet/unit/enviii/QMP6988%20Datasheet.pdf): pressure [PGN: 130314]
 * [SHT30](https://m5stack.oss-cn-shenzhen.aliyuncs.com/resource/docs/datasheet/unit/SHT3x_Datasheet_digital.pdf): temperature and humidity [PGNs: 130312, 130313]
 * [M5-ENV3](https://docs.m5stack.com/en/unit/envIII): combination of QMP6988 and SHT30 [PGNs: 130314,130312, 130313]