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// SPDX-License-Identifier: GPL-2.0-or-later
// SPDX-FileCopyrightText: 2023 Kent Gibson <warthog618@gmail.com>
/* Minimal example of asynchronously watching for edges on a single line. */
#include <cstdlib>
#include <cstring>
#include <filesystem>
#include <gpiod.hpp>
#include <iomanip>
#include <iostream>
#include <poll.h>
namespace {
/* Example configuration - customize to suit your situation. */
const ::std::filesystem::path chip_path("/dev/gpiochip0");
const ::gpiod::line::offset line_offset = 5;
const char* edge_event_type_str(const ::gpiod::edge_event &event)
{
switch (event.type()) {
case ::gpiod::edge_event::event_type::RISING_EDGE:
return "Rising ";
case ::gpiod::edge_event::event_type::FALLING_EDGE:
return "Falling";
default:
return "Unknown";
}
}
} /* namespace */
int main()
{
/*
* Assume a button connecting the pin to ground, so pull it up and
* provide some debounce.
*/
auto request =
::gpiod::chip(chip_path)
.prepare_request()
.set_consumer("async-watch-line-value")
.add_line_settings(
line_offset,
::gpiod::line_settings()
.set_direction(
::gpiod::line::direction::INPUT)
.set_edge_detection(
::gpiod::line::edge::BOTH)
.set_bias(::gpiod::line::bias::PULL_UP)
.set_debounce_period(
std::chrono::milliseconds(10)))
.do_request();
/*
* A larger buffer is an optimisation for reading bursts of events from
* the kernel, but that is not necessary in this case, so 1 is fine.
*/
::gpiod::edge_event_buffer buffer(1);
struct pollfd pollfd;
pollfd.fd = request.fd();
pollfd.events = POLLIN;
for (;;) {
/*
* Other fds could be registered with the poll and be handled
* separately using the pollfd.revents after poll()
*/
auto ret = poll(&pollfd, 1, -1);
if (ret == -1) {
::std::cerr << "error waiting for edge events: "
<< strerror(errno) << ::std::endl;
return EXIT_FAILURE;
}
request.read_edge_events(buffer);
for (const auto& event : buffer)
::std::cout << "offset: " << event.line_offset()
<< " type: " << ::std::setw(7)
<< ::std::left << edge_event_type_str(event)
<< " event #" << event.line_seqno()
<< ::std::endl;
}
}
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