How to access barometer readings?

Question

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)
", 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.

mfetting · Answer

I found the following information related to the barameter sensor.

The LPS22HH device (from ST MicroElectronics) provides digital pressure output. Measurements are accessed via the LSM6DSO interface to the I2C bus.

The LSM6DSO acts as a sensor hub and is the I2C master on the secondary I2C bus to which the LPS22HH pressure sensor device is attached.

I would suggest looking at the code found in the AvnetStarterKitReferenceDesign project.

Starting with lps22hh_reg.h and lps22hh_reg.c

You will find the initialization and retrieval of data from the sensor in i2c.c

clem57 · Answer

mysliwiec_tech wrote: 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. ... (omitted for brevity) 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. If you want a broad overview kind of explanation, try this https://www.tutorialspoint.com/embedded_systems/index.htm . It is short on details, but great for giving you a understanding. With that, the details may make more sense.

mfetting · Answer

I understand, we share the same interest to continue learning. I spent time last night working through the OLED, and face similar questions. I have found it helpful to start with a working solution and then begin moving in the direction I want it to go. I want to learn about the OLED but the example wants to teaching me about IOT_CENTRAL_APPLICATION. First I will make the solution work, then I will dissect it to learn what I want to learn.

My approach would be to start with disassembling AvnetStarterKitReferenceDesign by removing the features you do not need. By removing the other sensors and leaving only the Barometer. That way you start from a position of a working solution and move towards learning why something is there. The who_am_i is a verification of the sensor/bus so that the program knows it is communicating with something it understands. It is a static variable defined in the .h file

/** Device Identification (Who am I) **/

#define LPS22HH_ID 0xB3U

I'm learning about the Azure Sphere as I go as well, but have many years of coding behind me.

How to access barometer readings?

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