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added c++ usage example for this driver #155

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32 changes: 29 additions & 3 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

This repository contains examples of *low-level* [platform-independent drivers]( http://www.st.com/content/st_com/en/products/embedded-software/mems-and-sensors-software/drivers-for-mems/c-driver-mems.html ) for [STMicroelectronics](www.st.com/mems) sensors. Sensor drivers and examples are written in C programming language.

If you are using [STM32Cube packages](https://www.st.com/en/ecosystems/stm32cube.html), evaluate also the *hardware abstractions* [STM32Cube-compatible drivers](https://github.com/STMicroelectronics/STM32Cube_MCU_Overall_Offer/blob/master/README.md#stm32cube-bsp-components-drivers).
If you are using [STM32Cube packages](https://www.st.com/en/ecosystems/stm32cube.html), evaluate also the *hardware abstractions* [STM32Cube-compatible drivers](https://github.com/STMicroelectronics/STM32Cube_MCU_Overall_Offer/blob/master/README.md#stm32cube-bsp-components-drivers).

The STMicroelectronics naming convention for driver repositories is:
- `PARTNUMBER` (*i.e. [hts221](https://github.com/STMicroelectronics/hts221)*) for *low-level platform-independent drivers*
Expand Down Expand Up @@ -65,8 +65,35 @@ dev_ctx.read_reg = platform_read;
```c
dev_ctx.handle = &platform_handle;
```
### 2.c Using the handle to integrate this driver in c++ classes

- Non static member functions of classes need an pointer to their own instance as first argument this is implicit done by the compiler.
- This libraries pass the ```ctx.handle ``` as first argument to the read and write Functions so we can store the pointer to the class instance there.
- When defining out platform member functions we must skip the first argument since this will be the this pointer
See example:

```c++
class MemsSensor{
public:
...
private:
int32_t platform_write(uint8_t reg, const uint8_t *bufp,uint16_t len);
int32_t platform_read(uint8_t reg, uint8_t *bufp,uint16_t len);
stmdev_ctx_t _dev_ctx={(stmdev_write_ptr) &MemsSensor::platform_write,
(stmdev_read_ptr) &MemsSensor::platform_read,
(stmdev_mdelay_ptr) NULL, // no delay function set
this};
}
```

- With in the classes code the driver functions can than easily be used with &_dev_ctx as first argument like:


### 2.b Required properties
```c++
lsm6dsrx_device_id_get(&_dev_ctx, &_whoamI);
```

### 2.c Required properties

> * A standard C language compiler for the target MCU
> * A C library for the target MCU and the desired interface (ie. SPI, I²C)
Expand Down Expand Up @@ -114,4 +141,3 @@ If a different MCU is used, please follow these steps:
**More information: [http://www.st.com](http://st.com/MEMS)**

**Copyright (C) 2018-2022 STMicroelectronics**