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Make a new guess at post-overflow DIV flags, based on tests.

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Specifically: for DIVU, stick with the current guess of a fixed set. For DIVS, leave N and Z alone.
This commit is contained in:
Thomas Harte 2020-01-03 23:44:49 -05:00
parent c7a5b054db
commit 7de1181213
1 changed files with 2 additions and 14 deletions
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16
Processors/68000/Implementation/68000Implementation.hpp
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@ -86,9 +86,6 @@ template <class T, bool dtack_is_implicit, bool signal_will_perform> void Proces
} }
if(active_step_->microcycle.data_select_active()) { if(active_step_->microcycle.data_select_active()) {
// TODO: if valid peripheral address is asserted, substitute a
// synhronous bus access.
// Check whether the processor needs to await DTack. // Check whether the processor needs to await DTack.
if(!dtack_is_implicit && !dtack_ && !bus_error_) { if(!dtack_is_implicit && !dtack_ && !bus_error_) {
execution_state_ = ExecutionState::WaitingForDTack; execution_state_ = ExecutionState::WaitingForDTack;
@ -999,12 +996,8 @@ template <class T, bool dtack_is_implicit, bool signal_will_perform> void Proces
const auto quotient = dividend / divisor; const auto quotient = dividend / divisor;
// If overflow would occur, appropriate flags are set and the result is not written back. // If overflow would occur, appropriate flags are set and the result is not written back.
if(quotient >= 65536) { if(quotient > 65535) {
overflow_flag_ = overflow_flag_ = zero_result_ = negative_flag_ = 1;
zero_result_ =
negative_flag_ = 1;
// TODO: Zero and Negative flags as above are merely sufficient
// to satisfy the tests I currentl have. What should they really be?
set_next_microcycle_length(HalfCycles(3*2*2)); set_next_microcycle_length(HalfCycles(3*2*2));
break; break;
} }
@ -1075,11 +1068,6 @@ template <class T, bool dtack_is_implicit, bool signal_will_perform> void Proces
if(quotient > 32767) { if(quotient > 32767) {
overflow_flag_ = 1; overflow_flag_ = 1;
set_next_microcycle_length(HalfCycles(6*2*2)); set_next_microcycle_length(HalfCycles(6*2*2));
// These are officially undefined for results that overflow, so the below is a guess.
zero_result_ = decltype(zero_result_)(dividend);
negative_flag_ = zero_result_ & 0x8000;
break; break;
} }