[英]accurate sampling in c++
我想對每秒從gpio獲得的值進行4000次采樣,目前我正在執行類似的操作:
std::vector<int> sample_a_chunk(unsigned int rate, unsigned int block_size_in_seconds) {
std::vector<std::int> data;
constexpr unsigned int times = rate * block_size_in_seconds;
constexpr unsigned int delay = 1000000 / rate; // microseconds
for (int j=0; j<times; j++) {
data.emplace_back(/* read the value from the gpio */);
std::this_thread::sleep_for(std::chrono::microseconds(delay));
}
return data;
}
但是根據參考,sleep_for可以保證至少等待指定的時間。
如何讓系統等待確切的時間,或者至少達到最佳的准確性? 我如何確定系統的時間分辨率?
我認為您可能可以實現的最好方法是使用絕對定時以避免漂移。
像這樣:
std::vector<int> sample_a_chunk(unsigned int rate,
unsigned int block_size_in_seconds)
{
using clock = std::chrono::steady_clock;
std::vector<int> data;
const auto times = rate * block_size_in_seconds;
const auto delay = std::chrono::microseconds{1000000 / rate};
auto next_sample = clock::now() + delay;
for(int j = 0; j < times; j++)
{
data.emplace_back(/* read the value from the gpio */);
std::this_thread::sleep_until(next_sample);
next_sample += delay; // don't refer back to clock, stay absolute
}
return data;
}
我會使用boost :: asio :: deadline_timer 。
#include <vector>
#define BOOST_ERROR_CODE_HEADER_ONLY 1
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
std::vector<int> sample_a_chunk(unsigned int rate, unsigned int block_size_in_seconds) {
std::vector<int> data;
const unsigned int times = rate * block_size_in_seconds;
auto expiration_time = boost::posix_time::microsec_clock::local_time();
const auto delay = boost::posix_time::microseconds(1000000/rate);
boost::asio::io_service io;
boost::asio::deadline_timer t(io);
for (unsigned int j=0; j < times; j++) {
expiration_time += delay;
data.emplace_back(/* read the value from the gpio */);
t.expires_at(expiration_time);
t.wait();
}
return data;
}
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