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Simplifies timing calculation expression.

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This commit is contained in:
Thomas Harte 2021-04-21 19:18:07 -04:00
parent 30a1a53c97
commit 9baa861742
2 changed files with 13 additions and 33 deletions
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42
Machines/Sinclair/ZXSpectrum/Video.hpp
View File

@ -63,9 +63,9 @@ template <VideoTiming timing> class Video {
// Number of cycles after first pixel fetch at which interrupt is first signalled.
int interrupt_time;
// Contention to apply, in half-cycles, as a function of number of half cycles since
// Contention to apply, in whole cycles, as a function of number of whole cycles since
// contention began.
int delays[16];
int delays[8];
};
static constexpr Timings get_timings() {
@ -98,17 +98,10 @@ template <VideoTiming timing> class Video {
.contention_duration = 129 * 2,
// i.e. interrupt is first signalled 14368 cycles before the first video fetch.
.interrupt_time = (1 + 228*311 - 14365 - 5) * 2,
.interrupt_time = (228*311 - 14365 - 5) * 2,
.delays = { // Should start at 14365
2, 1,
0, 0,
14, 13,
12, 11,
10, 9,
8, 7,
6, 5,
4, 3,
1, 0, 7, 6, 5, 4, 3, 2,
}
};
@ -123,17 +116,10 @@ template <VideoTiming timing> class Video {
.contention_leadin = 4 * 2,
.contention_duration = 128 * 2,
.interrupt_time = (1 + 228*311 - 14361 - 4) * 2,
.interrupt_time = (228*311 - 14361 - 4) * 2,
.delays = { // Should start at 14361.
12, 11,
10, 9,
8, 7,
6, 5,
4, 3,
2, 1,
0, 0,
0, 0,
6, 5, 4, 3, 2, 1, 0, 0
}
};
@ -148,17 +134,10 @@ template <VideoTiming timing> class Video {
.contention_leadin = 4 * 2,
.contention_duration = 128 * 2,
.interrupt_time = (1 + 224*312 - 14335 - 4) * 2,
.interrupt_time = (224*312 - 14335 - 4) * 2,
.delays = { // Should start at 14335.
12, 11,
10, 9,
8, 7,
6, 5,
4, 3,
2, 1,
0, 0,
0, 0,
6, 5, 4, 3, 2, 1, 0, 0
}
};
@ -377,9 +356,10 @@ template <VideoTiming timing> class Video {
@returns How many cycles the [ULA/gate array] would delay the CPU for if it were to recognise that contention
needs to be applied in @c offset half-cycles from now.
*/
int access_delay(HalfCycles offset) const {
HalfCycles access_delay(HalfCycles offset) const {
constexpr auto timings = get_timings();
const int delay_time = (time_into_frame_ + offset.as<int>() + timings.contention_leadin) % (timings.cycles_per_line * timings.lines_per_frame);
assert(!(delay_time&1));
// Check for a time within the no-contention window.
if(delay_time >= (191*timings.cycles_per_line + timings.contention_duration)) {
@ -391,7 +371,7 @@ template <VideoTiming timing> class Video {
return 0;
}
return timings.delays[time_into_line & 15];
return timings.delays[(time_into_line >> 1) & 7] * 2;
}
/*!

4
Machines/Sinclair/ZXSpectrum/ZXSpectrum.cpp
View File

@ -218,7 +218,7 @@ template<Model model> class ConcreteMachine:
cycle.operation >= PartialMachineCycle::ReadOpcodeStart &&
cycle.operation <= PartialMachineCycle::WriteStart) {
const HalfCycles delay = video_.last_valid()->access_delay(video_.time_since_flush() + HalfCycles(1));
const auto delay = video_.last_valid()->access_delay(video_.time_since_flush());
advance(cycle.length + delay);
return delay;
}
@ -269,7 +269,7 @@ template<Model model> class ConcreteMachine:
// These all start by loading the address bus, then set MREQ
// half a cycle later.
if(is_contended_[address >> 14]) {
const HalfCycles delay = video_.last_valid()->access_delay(video_.time_since_flush());
const auto delay = video_.last_valid()->access_delay(video_.time_since_flush());
advance(cycle.length + delay);
return delay;