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Apply blitter priority bit.

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This commit is contained in:
Thomas Harte 2022-07-26 16:07:26 -04:00
parent ce7f57f251
commit 804c12034c
1 changed files with 9 additions and 6 deletions
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15
Machines/Amiga/Chipset.cpp
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@ -635,8 +635,6 @@ template <int cycle, bool stop_if_cpu> bool Chipset::perform_cycle() {
} else { } else {
// Bitplanes having been dealt with, specific even-cycle responsibility // Bitplanes having been dealt with, specific even-cycle responsibility
// is just possibly to pass to the Copper. // is just possibly to pass to the Copper.
//
// The Blitter and CPU are dealt with outside of the odd/even test.
constexpr auto CopperEnabled = DMAFlag::AllBelow | DMAFlag::Copper; constexpr auto CopperEnabled = DMAFlag::AllBelow | DMAFlag::Copper;
if((dma_control_ & CopperEnabled) == CopperEnabled) { if((dma_control_ & CopperEnabled) == CopperEnabled) {
if(copper_.advance_dma(uint16_t(((y_ & 0xff) << 8) | cycle), blitter_.get_status())) { if(copper_.advance_dma(uint16_t(((y_ & 0xff) << 8) | cycle), blitter_.get_status())) {
@ -645,12 +643,17 @@ template <int cycle, bool stop_if_cpu> bool Chipset::perform_cycle() {
} else { } else {
copper_.stop(); copper_.stop();
} }
// Picking between the Blitter and CPU occurs below, if applicable.
// But if the Blitter priority bit isn't set then don't even give it
// a look-in — nothing else having claimed this slot, leave it vacant
// for the CPU.
if(!(dma_control_ & DMAFlag::BlitterPriority)) {
return true;
}
} }
// Down here: give first refusal to the Blitter, otherwise // Give first refusal to the Blitter (if enabled), otherwise pass on to the CPU.
// pass on to the CPU.
//
// TODO: Blitter nasty flag. Who owns that?
constexpr auto BlitterEnabled = DMAFlag::AllBelow | DMAFlag::Blitter; constexpr auto BlitterEnabled = DMAFlag::AllBelow | DMAFlag::Blitter;
return (dma_control_ & BlitterEnabled) != BlitterEnabled || !blitter_.advance_dma(); return (dma_control_ & BlitterEnabled) != BlitterEnabled || !blitter_.advance_dma();
} }