Project-M/Assets/_Project/Scripts/Simulation/HeartbeatSystem.cs

using Unity.Burst;
using Unity.Entities;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Smoke-test system: increments every <see cref="Heartbeat"/> once per tick.
    /// Default (no <c>[WorldSystemFilter]</c>) so it runs in the SimulationSystemGroup of
    /// every world. Burst-compiled and unmanaged (<see cref="ISystem"/>) per DOTS convention.
    /// </summary>
    [BurstCompile]
    public partial struct HeartbeatSystem : ISystem
    {
        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            foreach (var heartbeat in SystemAPI.Query<RefRW<Heartbeat>>())
            {
                heartbeat.ValueRW.Tick++;
            }
        }
    }
}