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    • Updated blank line and italic style authored by Luca Conterio's avatar Luca Conterio
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    Temperature-Sensor.md
    View page @ d25ecd62
    ......@@ -9,13 +9,13 @@ Here we will only consider reading the temperature data.
    ## Header file
    We define the methods that we will be implemented in the `cpp` file:
    - *init*: configure sensor driver. It returns a boolean indicating if the initialization was successful.
    - *checkWhoAmI*: every sensor has a special only-read register that contains a number called `who_am_i`. This method checks that the `who_am_i` value is equal to the default one specified in the sensor's datasheet (which in this case is `63`). It returns a boolean indicating if the `who_am_i` value is correct.
    - *getTemperature*: read the temperature from the sensor and return it. As described in the datasheet the temperature is an 8-bit 2-complement (`int8_t`) value with a resolution of 1 LSB/deg. It means that is can only output integer temperature values. Finally it is also told that reading zero from the sensor corresponds to 25 celsius degrees (so `TEMPERATURE_REF` is set to 25).
    - _init_: configure sensor driver. It returns a boolean indicating if the initialization was successful.
    - _checkWhoAmI_: every sensor has a special read_only register that contains a number called `who_am_i`. This method checks that the `who_am_i` value is equal to the default one specified in the sensor's datasheet (which in this case is `63`). It returns a boolean indicating if the `who_am_i` value is correct.
    - _getTemperature_: read the temperature from the sensor and return it. As described in the datasheet the temperature is an 8-bit 2-complement (`int8_t`) value with a resolution of 1 LSB/deg. It means that is can only output integer temperature values. Finally it is also told that reading zero from the sensor corresponds to 25 celsius degrees (so `TEMPERATURE_REF` is set to 25).
    We also need two other memebers:
    - *ODR*: it indicates the *output data rate* of the sensor.
    - *BDU*: it indicates the *block data update* mode. This can be set to continuous mode (i.e. the sensor continuously produces samples) or we can configure the sensor so that it outputs a new sample only after the previous one has been read.
    - _ODR_: it indicates the _output data rate_ of the sensor.
    - _BDU_: it indicates the _block data update_ mode. This can be set to continuous mode (i.e. the sensor continuously produces samples) or we can configure the sensor so that it outputs a new sample only after the previous one has been read.
    ```cpp
    #pragma once
    ......@@ -40,30 +40,31 @@ private:
    uint8_t odr;
    uint8_t bdu;
    const uint8_t WHO_AM_I_DEFAULT_VALUE = 63;
    const uint8_t TEMPERATURE_REF = 25;
    const uint8_t WHO_AM_I_VALUE = 63;
    const uint8_t TEMPERATURE_REF = 25;
    };
    ```
    In order to configure the *ODR* and *BDU* values we can define two `enum` that contain all the possible values for those two variables. All these values can be found in the sensor's datasheet.
    In order to configure the _ODR_ and _BDU_ values we can define two `enum` that contain all the possible values for those two variables. All these values can be found in the sensor's datasheet.
    Since the default value of _ODR_ is `ODR_POWER_DOWN` we have to set a different value in order for the sensor to work.
    ```cpp
    enum OutputDataRate : uint8_t
    {
    ODR_POWER_DOWN = 0, // 0000
    ODR_3_125_HZ = 1, // 0001, 3.125 Hz
    ODR_6_25_HZ = 2, // 0010, 6.25 Hz
    ODR_12_5_HZ = 3, // 0011, 12.5 Hz
    ODR_25_HZ = 4, // 0100
    ODR_50_HZ = 5, // 0101
    ODR_100_HZ = 6, // 0110, default value
    ODR_400_HZ = 7, // 0111
    ODR_800_HZ = 8, // 1000
    ODR_1600_HZ = 9 // 1001
    ODRPOWER_DOWN = 0, // default value
    ODR_3_125_HZ = 1,
    ODR_6_25_HZ = 2,
    ODR_12_5_HZ = 3,
    ODR_25_HZ = 4,
    ODR_50_HZ = 5,
    ODR_100_HZ = 6,
    ODR_400_HZ = 7,
    ODR_800_HZ = 8,
    ODR_1600_HZ = 9
    };
    enum BlockDataUpdate : uint8_t
    {
    CONTINUOUS_UPDATE_MODE = 0, // continuous update of accelerometer data
    CONTINUOUS_UPDATE_MODE = 0,
    UPDATE_AFTER_READ_MODE = 1 // values updated only when MSB and LSB are read
    };
    ```
    ......@@ -72,7 +73,7 @@ Finally in order to read the data from the sensor and to configure it we need so
    The registers that we need are:
    - The register that contains the `who_am_i` value.
    - The register from which we can read the temperature values.
    - The `CTRL_REG4` which is needed in order to configure the *ODR* and *BDU* values.
    - The `CTRL_REG4` which is needed in order to configure the _ODR_ and _BDU_ values.
    The registers addresses, of course, are specified in the sensor's datasheet.
    ```cpp
    ......@@ -85,7 +86,7 @@ enum Registers : uint8_t
    ```
    ## Cpp file
    Import the header file and in the constructor simply initialized the *odr* and *bdu* members:
    Import the header file and in the constructor simply initialize the *odr* and *bdu* members:
    ```cpp
    #pragma once
    ......@@ -103,7 +104,7 @@ bool TempSensor::checkWhoAmI()
    {
    uint8_t who_am_i = spi_driver.read(WHO_AM_I_REG);
    if (who_am_i == WHO_AM_I_DEFAULT_VALUE)
    if (who_am_i == WHO_AM_I_VALUE)
    {
    return true;
    }
    ......@@ -113,16 +114,16 @@ bool TempSensor::checkWhoAmI()
    ```
    #### Configure the sensor
    During sensor's initialization, if the *checkWhoAmI* method returns `false`, then the initialization fails.
    To configure the *ODR* and *BDU* we have to set their values in the `CTRL_REG4` register of the sensor. We have to compute the value to be written to the register's address.
    During sensor's initialization, if the _checkWhoAmI_ method returns `false`, then the initialization fails.
    To configure the _ODR_ and _BDU_ we have to set their values in the `CTRL_REG4` register of the sensor. We have to compute the value to be written to the register's address.
    The `CTRL_REG4` register has the following 8-bits structure (LSB on the right and MSB on the left):
    | **ODR3** | **ODR2** | **ODR1** | **ODR0** | **BDU** | Zen | Yen | Xen |
    |----------|----------|----------|----------|----------|------|------|------|
    As we can se we have to shift the *BDU* value by 3 positions to the left and the *ODR* value by 4 position to the left. We can achieve this result through a *bitwise OR*.
    As we can se we have to shift the *BDU* value by 3 positions to the left and the *ODR* value by 4 positions to the left. We can achieve this result through a *bitwise OR*.
    Finally we can write the resulting value to the `CTRL_REG4` register's address using the SPI driver.
    ```cpp
    ......@@ -141,7 +142,7 @@ bool TempSensor::init()
    }
    ```
    #### Read temperature
    #### Read the temperature
    In order to read the temperature sample the only things we need is to read the `OUT_T` register through the SPI driver, rembering to add the `TEMPERATURE_REF` value to all the samples:
    ```cpp
    int8_t TempSensor::getTemperature()
    ......@@ -154,8 +155,8 @@ int8_t TempSensor::getTemperature()
    ```
    ## Create your entrypoint
    In `src/entrypoints` add a file called `test-tempsensor.cpp`
    In `src/entrypoints` add a file called `test-tempsensor.cpp`.
    A simple entrypoint creates a `TempSensor` object and periodically reads the temperature value:
    ```cpp
    #include <Common.h>
    ......