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* The Sensor class represents a variety of sensors that can be attached
* to a robot, allowing for a base set of APIs that make them
* easier to use.
#include <cstdint>
#include <cstddef>
#include <unistd.h>
#include <sys/eventfd.h>
namespace PiWars {
class Sensor {
// Initialize the base Sensor class
Sensor() : _enabled(false) {
_fd = eventfd(0, EFD_NONBLOCK);
~Sensor() {
// Returns the FD that threads can block on when waiting
// for sensor data to change.
// @returns The File descriptor a thread can block on
int getFD() { return _fd; };
// Returns if the sensor has been enabled
// @returns True is the sensor has been enabled
// false otherwise
bool isEnabled() { return _enabled; }
// Checks if the sensor is present. Some sensors can be dynamically
// added or removed from the robot, or turned on and off, so arn't
// always available for use.
// @returns true if the sensor exists
virtual bool exists() = 0;
// Enables the sensor ready for use.
// Some sensors use additional power or CPU resources
// when running, so we only want to enable them when
// we're ready to use them
// @returns true if successfully enabled
bool enable() { _enabled = true; return true; }
// Disable a sensor, potentially reducing power or CPU usage
void disable() { _enabled = false; }
// Called when the sensor data is changed, allowing any sleeping threads
// to be awoken
void changed() {
uint64_t value = 1;
write(_fd, &value, sizeof(value));
bool _enabled; //<! Used to indicate if a sensor is currently enabled
int _fd; //<! The eventfd file descriptor
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