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Added attribution and commentary on rotation speeds.

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This commit is contained in:
Thomas Harte 2019-07-10 16:22:06 -04:00
parent 1657f8768c
commit 6cfaf920ee
1 changed files with 33 additions and 20 deletions
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53
Components/DiskII/MacintoshDoubleDensityDrive.cpp
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@ -19,6 +19,39 @@ DoubleDensityDrive::DoubleDensityDrive(int input_clock_rate, bool is_800k) :
}
}
// MARK: - Speed Selection
void DoubleDensityDrive::did_step(Storage::Disk::HeadPosition to_position) {
// The 800kb drive automatically selects rotation speed as a function of
// head position; the 400kb drive doesn't do so.
if(is_800k_) {
/*
Numbers below cribbed from the Kryoflux forums; specifically:
https://forum.kryoflux.com/viewtopic.php?t=1090
They can almost be worked out algorithmically, since the point is to
produce an almost-constant value for speed*(number of sectors), and:
393.3807 * 12 = 4720.5684
429.1723 * 11 = 4720.895421
472.1435 * 10 = 4721.435
524.5672 * 9 = 4721.1048
590.1098 * 8 = 4720.8784
So 4721 / (number of sectors per track in zone) would give essentially
the same results.
*/
const int zone = to_position.as_int() >> 4;
switch(zone) {
case 0: set_rotation_speed(393.3807f); break;
case 1: set_rotation_speed(429.1723f); break;
case 2: set_rotation_speed(472.1435f); break;
case 3: set_rotation_speed(524.5672f); break;
default: set_rotation_speed(590.1098f); break;
}
}
}
// MARK: - Control input/output.
void DoubleDensityDrive::set_enabled(bool) {
@ -132,23 +165,3 @@ bool DoubleDensityDrive::read() {
void DoubleDensityDrive::write(bool value) {
}
// MARK: - Speed Selection
void DoubleDensityDrive::did_step(Storage::Disk::HeadPosition to_position) {
// The 800kb drive automatically selects rotation speed as a function of
// head position; the 400kb drive doesn't do so.
if(is_800k_) {
/*
Numbers below cribbed from the Kryoflux forums.
*/
const int zone = to_position.as_int() >> 4;
switch(zone) {
case 0: set_rotation_speed(393.3807f); break;
case 1: set_rotation_speed(429.1723f); break;
case 2: set_rotation_speed(472.1435f); break;
case 3: set_rotation_speed(524.5672f); break;
default: set_rotation_speed(590.1098f); break;
}
}
}