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260843e5b1
On the assumption that any relevant DC offset will fall out in the wash. This causes one 400kb disk to boot in a Macintosh 128kb, another couple to do reasonably well. So it's better than what was here before.
53 lines
1.5 KiB
C++
53 lines
1.5 KiB
C++
//
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// DriveSpeedAccumulator.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 01/06/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#include "DriveSpeedAccumulator.hpp"
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using namespace Apple::Macintosh;
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void DriveSpeedAccumulator::post_sample(uint8_t sample) {
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if(!number_of_drives_) return;
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// An Euler-esque approximation is used here: just collect all
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// the samples until there is a certain small quantity of them,
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// then produce a new estimate of rotation speed and start the
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// buffer afresh.
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samples_[sample_pointer_] = sample;
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++sample_pointer_;
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if(sample_pointer_ == samples_.size()) {
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sample_pointer_ = 0;
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// Treat 33 as a zero point and count zero crossings; then approximate
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// the RPM from the frequency of those.
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int samples_over = 0;
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int sum = 0;
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const uint8_t centre = 33;
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for(size_t c = 0; c < 512; ++c) {
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if(samples_[c] > centre) ++ samples_over;
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sum += samples_[c];
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}
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// TODO: if the above is the correct test, do it on sample receipt rather than
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// bothering with an intermediate buffer.
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// The below fits for a function like `a + bc`.
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const float rotation_speed = (float(sum) * 0.052896440564137f) - 259.0f;
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for(int c = 0; c < number_of_drives_; ++c) {
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drives_[c]->set_rotation_speed(rotation_speed);
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}
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// printf("RPM: %0.2f (%d over; %d sum)\n", rotation_speed, samples_over, sum);
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}
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}
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void DriveSpeedAccumulator::add_drive(Apple::Macintosh::DoubleDensityDrive *drive) {
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drives_[number_of_drives_] = drive;
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++number_of_drives_;
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}
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