I2C Driver sample
Using the I2C driver for the SC-OBC Module A1, this application retrieves temperature data from the sensor on the Development Board and displays it on the console. The sample application is available in I2C sample.
Explain the sample code
Directory Name
The directory name and structure for the sample application can be chosen freely.
In this example, we use the directory name samples/i2c.
CMakeLists.txt
A CMakeLists.txt file must be placed directly under the application directory.
# Copyright (c) 2025 Space Cubics Inc.
# SPDX-License-Identifier: Apache-2.0
cmake_minimum_required(VERSION 3.20.0)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(i2c-sample)
target_sources(app PRIVATE src/main.c)Here, the parts that need to be modified for each application are explained.
-
project: Specify the desired project name
-
target_sources: Specify the source code file(s)
prj.conf
Additional Kconfig parameters required for running the application can be specified.
As this example uses I2C, it is necessary to set CONFIG_I2C=y.
And, to display temperature data of type float using printf, it is necessary to enable CONFIG_PICOLIBC_IO_FLOAT.
For more information about CONFIG_PICOLIBC_IO_FLOAT, refer to CONFIG_PICOLIBC_IO_FLOAT.
CONFIG_I2C=y
CONFIG_PICOLIBC_IO_FLOAT=ySource code
The source code is shown below. Details will be explained separately.
/*
* Copyright (c) 2025 Space Cubics Inc.
*
* SPDX-License-Identifier: Apache-2.0
*/
#include <zephyr/drivers/i2c.h>
#define TMP175_I2C_ADDR (0x4B)
#define TMP175_TEMP_REG (0x00)
int main(void)
{
int ret;
uint8_t data[2];
float temp;
const struct device *i2c = DEVICE_DT_GET(DT_NODELABEL(i2c0));
if (!device_is_ready(i2c)) {
printf("I2C device is not ready\n");
ret = -ENODEV;
goto end;
}
ret = i2c_burst_read(i2c, TMP175_I2C_ADDR, TMP175_TEMP_REG, data, ARRAY_SIZE(data));
if (ret < 0) {
printf("Failed to read from Temperature Sensor (%d)\n", ret);
goto end;
}
/*
* The TMP175 temperature sensor provides temperature data with a 12-bit, and resolution
* is 0.0625°C. Since the data is transmitted over I2C as 16 bits, the lower 4 bits of
* the second byte should be discarded. For more details, please refer to the TMP175
* datasheet.
*/
data[1] = data[1] >> 4;
temp = (int8_t)data[0] + (float)data[1] * 0.0625f;
printf("Temperature: %.4f [deg]\n", (double)temp);
end:
return ret;
}Device structure
To use the I2C driver API, it is necessary to obtain the corresponding device structure.
There are several APIs available for retrieving a device structure, but in this sample, DEVICE_DT_GET and DT_NODELABEL are used.
The label name specified in DT_NODELABEL must match the label defined in the DTS file.
The I2C device connected to the temperature sensor on the Development Board is defined in DTS overlay file for Development Board.
Although three FPGA I2C cores are available on the Development Board, the temperature sensor is connected to i2c0.
const struct device *i2c = DEVICE_DT_GET(DT_NODELABEL(i2c0));|
Because the DTS file may be defined across multiple sources via overlays, you may want to inspect the final merged DTS. This merged DTS is available in the following file under the build directory.
|
Validate that I2C device is ready
Validate that I2C device is ready. If the I2C device is not properly initialized, it will return false.
if (!device_is_ready(i2c)) {
printf("I2C device is not ready\n");
ret = -ENODEV;
goto end;
}I2C driver API
The APIs provided by the I2C driver are documented in the I2C interface.
In this example, it is necessary to read 2 bytes of temperature data from the sensor, so the i2c_burst_read API is used to perform a multi-byte read from the I2C device.
The second argument specifies the slave address of the I2C device. For the TMP175 temperature sensor used in this example, the slave address is set to 0x4B.
The third argument specifies the register address from which the temperature data will be read.
This register address must be obtained from the TMP175 datasheet.
For TMP175, the temperature register address is 0x00.
ret = i2c_burst_read(i2c, TMP175_I2C_ADDR, TMP175_TEMP_REG, data, ARRAY_SIZE(data));Calculate temperature data
The TMP175 temperature data is represented in 12 bits, and its resolution is 0.0625. Therefore, the raw value is converted before being printed to the console.
For more details, please refer to the TMP175 datasheet.
data[1] = data[1] >> 4;
temp = (int8_t)data[0] + (float)data[1] * 0.0625f;Check the DIP Switch status
| To access the temperature sensor on the Development Board, bit7 (SCL) and bit8 (SDA) of DIP Switch (SW1) must be turned ON. If they are currently OFF, please switch them ON. |
Open console
Connect the cable between your SC-OBC Module A1 and your PC, then open the console in a terminal:
tio /dev/ttyUSB2| To use the Zephyr console, bit3 (RX) and bit4 (TX) of DIP Switch (SW1) must be turned ON. If they are currently OFF, please switch them ON. |