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Starts poking at a pure total-based formula.

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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.
This commit is contained in:
Thomas Harte 2019-07-31 12:42:23 -04:00
parent e3f22e5787
commit 260843e5b1
1 changed files with 5 additions and 4 deletions
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9
Machines/Apple/Macintosh/DriveSpeedAccumulator.cpp
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@ -26,22 +26,23 @@ void DriveSpeedAccumulator::post_sample(uint8_t sample) {
// Treat 33 as a zero point and count zero crossings; then approximate
// the RPM from the frequency of those.
int samples_over = 0;
int sum = 0;
const uint8_t centre = 33;
for(size_t c = 0; c < 512; ++c) {
if(samples_[c] > centre) ++ samples_over;
sum += samples_[c];
}
// TODO: if the above is the correct test, do it on sample receipt rather than
// bothering with an intermediate buffer.
// The below fits for a function like `a + bc`; I'm not sure it's
const float duty_cycle = float(samples_over) / float(samples_.size());
const float rotation_speed = 392.0f + duty_cycle * 19.95f;
// The below fits for a function like `a + bc`.
const float rotation_speed = (float(sum) * 0.052896440564137f) - 259.0f;
for(int c = 0; c < number_of_drives_; ++c) {
drives_[c]->set_rotation_speed(rotation_speed);
}
// printf("RPM: %0.2f (%d over)\n", rotation_speed, samples_over);
// printf("RPM: %0.2f (%d over; %d sum)\n", rotation_speed, samples_over, sum);
}
}