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This repository contains the implementation of the Sensirion I2C and SHDLC protocol and some commonly used functions for sensor implementations. It is a dependency of the Sensirion embedded sensor drivers. Sensirion sensors all use a protocol on top of the I2C/UART communications layer. There are two of those kinds of protocols used by Sensirion sensors, one for UART communication, called SHDLC, and one for I2C communication. To keep this implementation in one place only, this repository exists and is used by all embedded drivers.

It should not be necessary to clone this repository independently, and we recommend to clone the repository recursively from the respective projects.

If you're looking for sensor drivers, please refer to the release bundles (zip files) from the respective projects. An overview is listed at https://github.com/Sensirion/info#repositories

Repository content

The source code in this repository is spilt into three parts: Common code, I2C protocol and SHDLC protocol.

Common

In the common/ folder are three files. sensirion_config.h is the general configuration file. Depending on your hardware you will need to edit this. For more information, see the section named sensirion_config.h further down in this document. There are also the two files sensirion_common.[ch]. These contain common helper functions used by both UART and I2C sensor drivers.

I2C

In the i2c/ folder is the implementation of the protocol used by Sensirion sensors for I2C communication. This implementation is spilt into two parts. The implementation of the high level protocol in the files sensirion_i2c.[ch] and a hardware abstraction layer in sensirion_i2c_hal.[ch]. In sensirion_i2c.[ch] all the implementation details (CRC calculation, byte order swapping, ...) of Sensirion's I2C communication are implemented. The finished frame is then sent to the attached hardware using the Hardware Abstraction Layer (HAL) in the other two files. Since the way how to send out this frame depends on underlying hardware and operating system, we provide different implementations for that part of the code. You can find these in the folder i2c/sample-implementations/ for the most common platforms. We even provide a implementation for software I2C using bit-banging on GPIOs in i2c/sample-implementations/GPIO_bit_banging/. If we don't provide code for your platform yet you can use the provided template structure in the i2c/ folder to implement it yourself. We're very happy to review and include more architectures in the form of a pull request on GitHub.

SHDLC

The shdlc folder contains the implementation of the protocol used by Sensirion sensors for UART communication. These sensors use Sensirion's own SHDLC protocol. The high level implementation of this protocol can be found in sensirion_shdlc.[ch] and the hardware abstraction layer in sensirion_uart_hal.[ch]. In sensirion_shdlc.[ch] all the implementation details (checksum calculation, byte order swapping, frame construction, ...) of Sensirion's SHDLC communication are implemented. The finished frame is then sent to your hardware using the HAL in the other two files. Since the way how to send out this frame depends on underlying hardware and operating system we provide different implementations for that part of the code. You can find these in the folder shdlc/sample-implementaions/ for the most common platforms. If we we don't provide code for your platform yet, you can use the provided template structure in the shdlc/ folder to implement it yourself. We're very happy to review and include more architectures in the form of a pull request on GitHub.

Files to be adjusted by the User

The following files are the only ones you should need to change if you want to use the functionality of embedded-common. Here we explain which changes need to be made according to your hardware platform.

sensirion_config.h

In this file we keep all the included libraries for our drivers. It is located in the common/ folder. The two libraries our drivers use are <stdint.h> and <stdlib.h>. The features we use out of those libraries is standard integer sizes from <stdint.h> and NULL from <stdlib.h>. We assume that those libraries are provided by your toolchain, compiler or are available on your system, so we have include directives for them. If this is not the case on your platform you need to specify the following integer types yourself:

In addition to that you will need to specify NULL. For both we have a commented template where just need to fill in your system specific values.

Make sure you specify the whole range (64bit sized integers are used on a 32bit system for some sensor data).

sensirion_i2c_hal.c

As already explained earlier is all the I2C related code in this repository based on Sensirion's I2C HAL. It is defined in sensirion_i2c_hal.h and implemented in the corresponding .c file, both located in the i2c/ folder. To use the I2C part of embedded-common you either need to implement the functions in sensirion_i2c_hal.c or replace it with a sample implementation from i2c/sample-implementation/. If you want to use software I2C on GPIOs using bit banging, then there is a sample implementation for sensirion_i2c_hal.c in the GPIO_bit_banging folder but then you will have to implement the sensirion_sw_i2c.c file also located there. More about this in the README.md located in the GPIO_bit_banging folder.

sensirion_shdlc_hal.c

As already explained earlier is all the SHDLC and UART related code in this repository based on Sensirion's UART HAL. It is defined in sensirion_uart_hal.h and implemented in the corresponding .c file, both located in the shdlc/ folder. To use the SHDLC part of embedded-common you either need to implement the sensirion_uart_hal.c file or replace the unimplemented version in shdlc/ with the correct sample implementation from shdlc/sample-implementation/.