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Add quick clock-rate notes.

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This commit is contained in:
Thomas Harte 2022-12-26 22:56:45 -05:00
parent cdbd821913
commit 99ced5476f
1 changed files with 20 additions and 0 deletions
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20
Components/9918/9918.cpp
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@ -15,6 +15,26 @@
using namespace TI::TMS;
//
// TODO notes.
//
// The TMS and Master System VDP run at 342 cycles/line.
//
// The Mega Drive VDP has 3420 master clocks per line, which it divides
// by 4 or 5 depending on pixel rate and which part of a line is active.
// (And, presumably, by 10 if operating in Master System mode?)
// Cf. https://gendev.spritesmind.net/forum/viewtopic.php?t=851 etc.
//
// The MSX2+ Yamaha VDPs have 1368 cycles/line.
//
// So if clock scaling were common, it would need to be to:
//
// 3420 = 2 * 2 * 3 * 3 * 5 * 19
// 1368 = 2 * 2 * 2 * 3 * 3 * 19
//
// => 2^3 * 3^2 * 5 * 19 = 6840
// ... which
namespace {
constexpr uint8_t StatusInterrupt = 0x80;