Compile-Time Timer Reload

Question

Problem: Compile-Time Timer Reload. Solve this hands-on electronics task on EWskills.

Accepted Answer

#include 
using namespace std;

// Compute timer reload at compile time (with rounding)
constexpr unsigned int computeReload(unsigned int clockHz,
                                     unsigned int intervalMs) {
    return (clockHz * intervalMs + 500) / 1000;
}

// Precomputed reload values for 1 ms, 10 ms, 100 ms
constexpr unsigned int RELOAD_TABLE[3] = {
    computeReload(1'000'000, 1),
    computeReload(1'000'000, 10),
    computeReload(1'000'000, 100)
};

int main() {
    int idx;
    cin >> idx;

    cout << RELOAD_TABLE[idx];
    return 0;
}

Explanation & Logic Summary:

Hardware timers require precise reload values for periodic interrupts
constexpr ensures all reload values are computed at compile time
The reload table is stored in Flash, not RAM
Rounding ensures timing accuracy
Runtime code only performs array indexing

Firmware Relevance & Real Embedded Meaning:

Timer reload values are fundamental to RTOS ticks, control loops, and sampling
Runtime division is slow and risky on MCUs
Compile-time computation ensures:
- Deterministic timing
- Zero runtime math
- Zero RAM usage
- High reliability in safety-critical firmware

This mirrors how real MCU HALs and RTOS kernels configure timers internally.

65. Compile-Time Timer Reload