dither_reserve_mW()

fl::u32 dither_reserve_mW

(

fl::span< const CRGB >

leds

)

The most BINARY_DITHER can add to one latched frame of leds, in mW (#4342, contract R4: "quantization reserve").

Dither is applied before scaling and only ever raises a lit channel – dither() is b ? qadd8(b, d) : 0 – by up to two output codes at any non-zero brightness (the offset d <= 256/s is scaled back by s, and the FASTLED_SCALE8_FIXED rounding can carry once more). So the reserve is two codes on every lit channel, at the power model's steepest single-code step, rounded up. It does not scale with brightness, which is why the limiter adds it to the fixed part of the demand rather than the scaled part.

Definition at line 485 of file power_mgt.cpp.hpp.

                                                 {
    fl::u32 lit_r = 0, lit_g = 0, lit_b = 0;
    for (fl::size i = 0; i < leds.size(); ++i) {
        // A zero channel is never dithered: `dither()` returns 0 for it.
        lit_r += leds[i].r != 0 ? 1u : 0u;
        lit_g += leds[i].g != 0 ? 1u : 0u;
        lit_b += leds[i].b != 0 ? 1u : 0u;
    }
    const PowerModelRGB& model = gPowerModel();
    const fl::u64 per_code =
        static_cast<fl::u64>(lit_r) * model.red_mW +
        static_cast<fl::u64>(lit_g) * model.green_mW +
        static_cast<fl::u64>(lit_b) * model.blue_mW;
    // Same >> 8 as the estimator, rounded up: this is a bound, and truncating
    // it would hand back the under-charge it exists to remove.
    const fl::u64 scaled = per_code * kDitherReserveCodes * max_power_step();
    const fl::u64 reserve = (scaled + 255) >> 8;
    // Saturate rather than wrap: an under-stated reserve is the failure this
    // exists to prevent.
    return reserve > 0xFFFFFFFFu ? 0xFFFFFFFFu : static_cast<fl::u32>(reserve);
}

References PowerModelRGB::blue_mW, gPowerModel(), PowerModelRGB::green_mW, kDitherReserveCodes, leds, max_power_step(), and PowerModelRGB::red_mW.

Referenced by controller_dither_reserve_mW().

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