Actions
Forum Thread Details
  • State Suggested Answer
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 48 subscribers
  • Views 822 views
  • Users 0 members are here
Related

How to access barometer readings?

mysliwiec_tech

I'm a novice in C and in embedded programming. Let's say I started with Azure Sphere as there was an occasion to enter to this field in a cheap way. As a training I have successfully accessed the readings from gyro and accelerometer, but having issues with accessing pressure readings. I understand that between the barometer and ARM there is the accelerometer (which functions like some "proxy" as I understand). Can someone explain to me how to access the:

  • WHO_AM_I register of the barometer, - if I get this, I think I will easily get to point bellow
  • readings of air pressure.

Reading the source code of an example is difficult to me (probably not yet adjusted to my level yet). I'm looking for someone to point me to what registers in sequence I have to write, in order to get value of WHO_AM_I, with the explanation why it is done that way.

So far I have that:

static const uint8_t lsm6dsoAddress = 0x6A;
static const uint8_t lps22hh = 0x5C;


static const uint8_t regId = 0x01;
static const uint16_t hub[] = { regId, 0x40 }; //setting SHUB_REG_ACCESS flag
uint8_t val;

static const uint8_t masterConfigRegId = 0x14;
static const uint16_t masterOn[] = { masterConfigRegId, 0x04 }; //setting MASTER_ON flag

static const uint16_t slv0Addr[] = { 0x15, 0xB9 }; //read address of barometer
static const uint16_t slv0WhoAmIRegId[] = { 0x16, 0x0F }; //who_am_i register of barometer
uint8_t actualWhoAmI;

int i2cFd = I2CMaster_Open(2);
if (i2cFd < 0) {
Log_Debug("ERROR: I2CMaster_Open: errno=%d (%s)\n", errno, strerror(errno));
return -1;
}

I2CMaster_Write(i2cFd, lsm6dsoAddress, &hub, 8); //enabling the access to the hub registers

I2CMaster_Write(i2cFd, lsm6dsoAddress, &masterOn, 16); //thought I need to enable that, so I can access the barometer

I2CMaster_Write(i2cFd, lsm6dsoAddress, &slv0Addr, 16); //setting that so the next write will go to barometer directky
I2CMaster_WriteThenRead(i2cFd, lsm6dsoAddress, &slv0WhoAmIRegId, 16, &actualWhoAmI, 8); //getting the value of who_am_i register - unfortunately the program returns 0x00 here
Log_Debug("0x%02x", actualWhoAmI);
return 0;

Please forgive me the lack of error catching (doing that for simplification). Just want to understand the approach to my problem. I'm really eager to start learning by doing + learn how to read technical documentation, but I think so far I lack some crucial points.

Parents
  • 0

    I2CMaster_WriteThenRead fucntion documentation:

     

    https://docs.microsoft.com/en-us/azure-sphere/reference/applibs-reference/applibs-i2c/function-i2cmaster-writethenread

     

    azure-sphere-sample code from main.c (https://github.com/Azure/azure-sphere-samples/blob/master/Samples/I2C/I2C_LSM6DS3_HighLevelApp/I2C_LSM6DS3_HighLevelApp/… )

     

     

    // Demonstrates three ways of reading data from the attached device.
// This also works as a smoke test to ensure the Azure Sphere can talk to the I2C device.
static int ReadWhoAmI(void)
{
    // DocID026899 Rev 10, S9.11, WHO_AM_I (0Fh); has fixed value 0x69.
    static const uint8_t whoAmIRegId = 0x0F;
    static const uint8_t expectedWhoAmI = 0x69;
    uint8_t actualWhoAmI;


    // Read register value using AppLibs combination read and write API.
    ssize_t transferredBytes =
        I2CMaster_WriteThenRead(i2cFd, lsm6ds3Address, &whoAmIRegId, sizeof(whoAmIRegId),
                                &actualWhoAmI, sizeof(actualWhoAmI));
    if (!CheckTransferSize("I2CMaster_WriteThenRead (WHO_AM_I)",
                           sizeof(whoAmIRegId) + sizeof(actualWhoAmI), transferredBytes)) {
        return -1;
    }
    Log_Debug("INFO: WHO_AM_I=0x%02x (I2CMaster_WriteThenRead)\n", actualWhoAmI);
    if (actualWhoAmI != expectedWhoAmI) {
        Log_Debug("ERROR: Unexpected WHO_AM_I value.\n");
        return -1;
    }


    // Read register value using AppLibs separate read and write APIs.
    transferredBytes = I2CMaster_Write(i2cFd, lsm6ds3Address, &whoAmIRegId, sizeof(whoAmIRegId));
    if (!CheckTransferSize("I2CMaster_Write (WHO_AM_I)", sizeof(whoAmIRegId), transferredBytes)) {
        return -1;
    }
    transferredBytes = I2CMaster_Read(i2cFd, lsm6ds3Address, &actualWhoAmI, sizeof(actualWhoAmI));
    if (!CheckTransferSize("I2CMaster_Read (WHO_AM_I)", sizeof(actualWhoAmI), transferredBytes)) {
        return -1;
    }
    Log_Debug("INFO: WHO_AM_I=0x%02x (I2CMaster_Write + I2CMaster_Read)\n", actualWhoAmI);
    if (actualWhoAmI != expectedWhoAmI) {
        Log_Debug("ERROR: Unexpected WHO_AM_I value.\n");
        return -1;
    }


    // Read register value using POSIX APIs.
    // This uses the I2C target address which was set earlier with
    // I2CMaster_SetDefaultTargetAddress.
    transferredBytes = write(i2cFd, &whoAmIRegId, sizeof(whoAmIRegId));
    if (!CheckTransferSize("write (WHO_AM_I)", sizeof(whoAmIRegId), transferredBytes)) {
        return -1;
    }
    transferredBytes = read(i2cFd, &actualWhoAmI, sizeof(actualWhoAmI));
    if (!CheckTransferSize("read (WHO_AM_I)", sizeof(actualWhoAmI), transferredBytes)) {
        return -1;
    }
    Log_Debug("INFO: WHO_AM_I=0x%02x (POSIX read + write)\n", actualWhoAmI);
    if (actualWhoAmI != expectedWhoAmI) {
        Log_Debug("ERROR: Unexpected WHO_AM_I value.\n");
        return -1;
    }


    return 0;
}

Reply
  • 0

    I2CMaster_WriteThenRead fucntion documentation:

     

    https://docs.microsoft.com/en-us/azure-sphere/reference/applibs-reference/applibs-i2c/function-i2cmaster-writethenread

     

    azure-sphere-sample code from main.c (https://github.com/Azure/azure-sphere-samples/blob/master/Samples/I2C/I2C_LSM6DS3_HighLevelApp/I2C_LSM6DS3_HighLevelApp/… )

     

     

    // Demonstrates three ways of reading data from the attached device.
// This also works as a smoke test to ensure the Azure Sphere can talk to the I2C device.
static int ReadWhoAmI(void)
{
    // DocID026899 Rev 10, S9.11, WHO_AM_I (0Fh); has fixed value 0x69.
    static const uint8_t whoAmIRegId = 0x0F;
    static const uint8_t expectedWhoAmI = 0x69;
    uint8_t actualWhoAmI;


    // Read register value using AppLibs combination read and write API.
    ssize_t transferredBytes =
        I2CMaster_WriteThenRead(i2cFd, lsm6ds3Address, &whoAmIRegId, sizeof(whoAmIRegId),
                                &actualWhoAmI, sizeof(actualWhoAmI));
    if (!CheckTransferSize("I2CMaster_WriteThenRead (WHO_AM_I)",
                           sizeof(whoAmIRegId) + sizeof(actualWhoAmI), transferredBytes)) {
        return -1;
    }
    Log_Debug("INFO: WHO_AM_I=0x%02x (I2CMaster_WriteThenRead)\n", actualWhoAmI);
    if (actualWhoAmI != expectedWhoAmI) {
        Log_Debug("ERROR: Unexpected WHO_AM_I value.\n");
        return -1;
    }


    // Read register value using AppLibs separate read and write APIs.
    transferredBytes = I2CMaster_Write(i2cFd, lsm6ds3Address, &whoAmIRegId, sizeof(whoAmIRegId));
    if (!CheckTransferSize("I2CMaster_Write (WHO_AM_I)", sizeof(whoAmIRegId), transferredBytes)) {
        return -1;
    }
    transferredBytes = I2CMaster_Read(i2cFd, lsm6ds3Address, &actualWhoAmI, sizeof(actualWhoAmI));
    if (!CheckTransferSize("I2CMaster_Read (WHO_AM_I)", sizeof(actualWhoAmI), transferredBytes)) {
        return -1;
    }
    Log_Debug("INFO: WHO_AM_I=0x%02x (I2CMaster_Write + I2CMaster_Read)\n", actualWhoAmI);
    if (actualWhoAmI != expectedWhoAmI) {
        Log_Debug("ERROR: Unexpected WHO_AM_I value.\n");
        return -1;
    }


    // Read register value using POSIX APIs.
    // This uses the I2C target address which was set earlier with
    // I2CMaster_SetDefaultTargetAddress.
    transferredBytes = write(i2cFd, &whoAmIRegId, sizeof(whoAmIRegId));
    if (!CheckTransferSize("write (WHO_AM_I)", sizeof(whoAmIRegId), transferredBytes)) {
        return -1;
    }
    transferredBytes = read(i2cFd, &actualWhoAmI, sizeof(actualWhoAmI));
    if (!CheckTransferSize("read (WHO_AM_I)", sizeof(actualWhoAmI), transferredBytes)) {
        return -1;
    }
    Log_Debug("INFO: WHO_AM_I=0x%02x (POSIX read + write)\n", actualWhoAmI);
    if (actualWhoAmI != expectedWhoAmI) {
        Log_Debug("ERROR: Unexpected WHO_AM_I value.\n");
        return -1;
    }


    return 0;
}

Children
No Data