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Adjust MDA clock; it's slightly slower than my guess.

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This commit is contained in:
Thomas Harte 2023-12-05 22:31:37 -05:00
parent 5576588c2d
commit c5ec9ae171
1 changed files with 10 additions and 5 deletions
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15
Machines/PCCompatible/MDA.hpp
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@ -28,11 +28,16 @@ class MDA {
} }
void run_for(Cycles cycles) { void run_for(Cycles cycles) {
// Input rate is the PIT rate of 1,193,182 Hz.
// MDA is actually clocked at 16.257 MHz; which is treated internally as 1,806,333.333333333333333... Hz
//
// The GCD of those two numbers is... 2. Oh well.
// I _think_ the MDA's CRTC is clocked at 14/9ths the PIT clock. // I _think_ the MDA's CRTC is clocked at 14/9ths the PIT clock.
// Do that conversion here. // Do that conversion here.
full_clock_ += 14 * cycles.as<int>(); full_clock_ += 8'128'500 * cycles.as<int>();
crtc_.run_for(Cycles(full_clock_ / 9)); crtc_.run_for(Cycles(full_clock_ / (596'591 * 9)));
full_clock_ %= 9; full_clock_ %= (596'591 * 9);
} }
template <int address> template <int address>
@ -64,13 +69,13 @@ class MDA {
} }
Outputs::Display::ScanStatus get_scaled_scan_status() const { Outputs::Display::ScanStatus get_scaled_scan_status() const {
return outputter_.crt.get_scaled_scan_status() * 9.0f / 14.0f; return outputter_.crt.get_scaled_scan_status() * 596591.0f / 8128500.0f;
} }
private: private:
struct CRTCOutputter { struct CRTCOutputter {
CRTCOutputter() : CRTCOutputter() :
crt(882, 9, 382, 3, Outputs::Display::InputDataType::Red2Green2Blue2) crt(882, 9, 370, 3, Outputs::Display::InputDataType::Red2Green2Blue2)
// TODO: really this should be a Luminance8 and set an appropriate modal tint colour; // TODO: really this should be a Luminance8 and set an appropriate modal tint colour;
// consider whether that's worth building into the scan target. // consider whether that's worth building into the scan target.
{ {