LineTiming.cs

using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
 
namespace OSDP.Net.Utilities
{
    internal static class LineTiming
    {
        private const int BitsPerCharacter = 10;

        private const int IdleCharacters = 2;

        private const double SpinThresholdMilliseconds = 16;

        public static TimeSpan ForCharacters(int baudRate, int characterCount) =>
            baudRate <= 0 || characterCount <= 0
                ? TimeSpan.Zero
                : TimeSpan.FromSeconds((double)(characterCount * BitsPerCharacter) / baudRate);

        public static TimeSpan IdleLine(int baudRate) => ForCharacters(baudRate, IdleCharacters);

        public static async Task WaitAsync(TimeSpan delay, long sinceTimestamp)
        {
            if (delay <= TimeSpan.Zero) return;
 
            long target = sinceTimestamp + (long)(delay.TotalSeconds * Stopwatch.Frequency);
 
            // A delay long enough to sleep through is slept off first, leaving only the imprecise
            // tail to spin. In practice the whole wait is spun: two characters is 2.08 ms at 9600
            // baud and less at every higher rate.
            double remaining = RemainingMilliseconds(target);
            if (remaining > SpinThresholdMilliseconds)
            {
                await Task.Delay((int)(remaining - SpinThresholdMilliseconds)).ConfigureAwait(false);
            }
 
            while (Stopwatch.GetTimestamp() < target)
            {
                Thread.SpinWait(50);
            }
        }
 
        private static double RemainingMilliseconds(long target) =>
            (target - Stopwatch.GetTimestamp()) * 1000.0 / Stopwatch.Frequency;
    }
}