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Clarify and slightly improve state machine.

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No more using the visible flag to permit a DMA control fetch.
This commit is contained in:
Thomas Harte 2022-07-19 15:39:57 -04:00
parent 0c6d7e07ee
commit 830704b4a9
2 changed files with 12 additions and 12 deletions
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2
Machines/Amiga/Chipset.cpp
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@ -611,7 +611,7 @@ template <int cycle, bool stop_if_cpu> bool Chipset::perform_cycle() {
constexpr auto sprite_id = (cycle - 0x16) >> 2;
static_assert(sprite_id >= 0 && sprite_id < std::tuple_size<decltype(sprites_)>::value);
if(sprites_[sprite_id].advance_dma(!(cycle&2))) {
if(sprites_[sprite_id].advance_dma((~cycle&2) >> 1)) {
return false;
}
}

22
Machines/Amiga/Sprites.cpp
View File

@ -59,35 +59,35 @@ void Sprite::advance_line(int y, bool is_end_of_blank) {
}
if(is_end_of_blank || y == v_stop_) {
dma_state_ = DMAState::FetchControl;
visible = true;
}
}
bool Sprite::advance_dma(int offset) {
if(!visible) return false;
assert(offset == 0 || offset == 1);
// Fetch another word.
// Determine which word would be fetched, if DMA occurs.
// A bit of a cheat.
const uint16_t next_word = ram_[pointer_[0] & ram_mask_];
++pointer_[0];
// Put the fetched word somewhere appropriate and update the DMA state.
switch(dma_state_) {
// i.e. stopped.
default: return false;
case DMAState::FetchControl:
if(offset) {
set_stop_and_control(next_word);
} else {
set_start_position(next_word);
}
return true;
break;
case DMAState::FetchImage:
set_image_data(1 - bool(offset), next_word);
return true;
if(!visible) return false;
set_image_data(1 - offset, next_word);
break;
}
return false;
// Acknowledge the fetch.
++pointer_[0];
return true;
}
template <int sprite> void TwoSpriteShifter::load(