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Restricts DTack delay to RAM and Shifter accesses.

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This commit is contained in:
Thomas Harte 2019-11-18 22:57:13 -05:00
parent 6990abc0d3
commit c04d2f6c6e
1 changed files with 6 additions and 2 deletions
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8
Machines/Atari/ST/AtariST.cpp
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@ -170,9 +170,14 @@ class ConcreteMachine:
} }
} }
auto address = cycle.word_address();
// If this is a new strobing of the address signal, test for bus error and pre-DTack delay. // If this is a new strobing of the address signal, test for bus error and pre-DTack delay.
//
// DTack delay rule: if accessing RAM or the shifter, align with the two cycles next available
// for the CPU to access that side of the bus.
HalfCycles delay(0); HalfCycles delay(0);
if(cycle.operation & Microcycle::NewAddress) { if((cycle.operation & Microcycle::NewAddress) && (address < ram_.size() || (address == (0xff8260 >> 1)))) {
// DTack will be implicit; work out how long until that should be, // DTack will be implicit; work out how long until that should be,
// and apply bus error constraints. // and apply bus error constraints.
const int i_phase = bus_phase_.as<int>() & 7; const int i_phase = bus_phase_.as<int>() & 7;
@ -184,7 +189,6 @@ class ConcreteMachine:
// TODO: presumably test is if(after declared memory size and (not supervisor or before hardware space)) bus_error? // TODO: presumably test is if(after declared memory size and (not supervisor or before hardware space)) bus_error?
} }
auto address = cycle.word_address();
uint16_t *memory = nullptr; uint16_t *memory = nullptr;
switch(memory_map_[address >> 15]) { switch(memory_map_[address >> 15]) {
default: default: