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Switch to idealised Nick clock rate.

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This commit is contained in:
Thomas Harte 2021-06-20 14:21:56 -04:00
parent 07dc26f8fa
commit 2fe15a6168
1 changed files with 5 additions and 8 deletions
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13
Machines/Enterprise/Enterprise.cpp
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@ -40,14 +40,11 @@ namespace Enterprise {
I shall _guess_ that the Enterprise stretches each line to 284 colour cycles rather than
reducing it to 283.
Therefore 912 cycles occurs in 284/283.7516 * 64 µs, which would appear to give an ideal
clock rate of around:
Therefore 912 cycles occurs in 284/283.7516 * 64 µs.
14,237,536.27 Hz.
Given that there's always some leeway in a receiver, I'm modelling that as 14,237,536 cycles,
which means that Nick runs 444923/125000 times as fast as the Z80. Which is around 3.56 times
as fast.
So one line = 181760000 / 2837516 µs = 45440000 / 709379 µs
=> one cycle = 45440000 / 709379*912 = 45440000 / 646953648 = 2840000 / 40434603 µs
=> clock rate of 40434603 / 2840000 Mhz
If that's true then the 6-cycle window is around 1.69 Z80 cycles long. Given that the Z80
clock in an Enterprise can be stopped in half-cycle increments only, the Z80 can only be
@ -376,7 +373,7 @@ class ConcreteMachine:
// MARK: - Chips.
CPU::Z80::Processor<ConcreteMachine, false, false> z80_;
JustInTimeActor<Nick, HalfCycles, 444923, 125000> nick_;
JustInTimeActor<Nick, HalfCycles, 40434603, 2840000> nick_;
bool previous_nick_interrupt_line_ = false;
// Cf. timing guesses above.
};