Sensor Daemon

Reads data from physical ports and writes data to shmem for other processes to use.

Dependencies

• Clang
• libi2c-dev
• libgpiod-dev

Creating a new sensor module

This deamon spawns variable many sensors with variably many interfaces. For example, imagine we have 2 ultrasound sensors and a hall effect sensor. We can instantiate of the following, and each will run in their own thread.

It is, therefor, necessary that each sensor module follows the following restricitions:

1. The module must be stateless. That is, all memory managment (references to the sensor obj, etc) are not handled by the module. Any call to any function must always return the same result.

2. The module must implement the following function with the following interfaces

   a) An init function in the form void *init(void **) {...}. The return must be the object reference that is used to interface with the remainder of the interface

   b) A read function in the form double read(void *sensor_object) {...}. The return is the value read and must be a double.

   c) A cleanup function int he form void cleanup(void *) which cleans up the object and all memory associated with it.

Interfacing sensor module with program

To add a sensor to this object, be sure to have a module that abides by the restrictions outlined above. Adding a sensor requires a single call to the sensor module. Instantiation, threading, etc is handled by the module. To add a sensor, call the int add_sensor(void \*init, void \*\*init_args, void \*cleanup, void \*read, int interval) where init is the function to instantiate sensor instance, init_args is a malloc´d ptr to the parameters needed by the init function, cleanupis the pointer to the cleanup function, read is the pointer to the read function, and interval is the number of useconds to wait between calling read.

Design choices

This interface was created to allow scalable sensor polling. The usleep(interval)was inspired by the long latency gpiod_events suffer (and hence poor timing results) because of their intterupt nature. Calling sleep allows the kernel to handle the distribution of events better than before, without interfering in any data-critical sections of the sensors.