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Apply E mode wrap for d,x and d,y only when DL = 0.

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This commit is contained in:
Thomas Harte 2022-09-09 16:02:35 -04:00
parent 45dc99fb9d
commit 98d3da62b5
1 changed files with 25 additions and 13 deletions
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38
Processors/65816/Implementation/65816Implementation.hpp
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@ -334,6 +334,7 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
case OperationConstructDirect: case OperationConstructDirect:
data_address_ = (registers_.direct + instruction_buffer_.value) & 0xffff; data_address_ = (registers_.direct + instruction_buffer_.value) & 0xffff;
data_address_increment_mask_ = 0x00'ff'ff; data_address_increment_mask_ = 0x00'ff'ff;
if(!(registers_.direct&0xff)) { if(!(registers_.direct&0xff)) {
// If the low byte is 0 and this is emulation mode, incrementing // If the low byte is 0 and this is emulation mode, incrementing
// is restricted to the low byte. // is restricted to the low byte.
@ -345,6 +346,7 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
case OperationConstructDirectLong: case OperationConstructDirectLong:
data_address_ = (registers_.direct + instruction_buffer_.value) & 0xffff; data_address_ = (registers_.direct + instruction_buffer_.value) & 0xffff;
data_address_increment_mask_ = 0x00'ff'ff; data_address_increment_mask_ = 0x00'ff'ff;
if(!(registers_.direct&0xff)) { if(!(registers_.direct&0xff)) {
++next_op_; ++next_op_;
} }
@ -380,31 +382,41 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
data_buffer_.clear(); data_buffer_.clear();
continue; continue;
// TODO: confirm incorrect_data_address_ below.
case OperationConstructDirectX: case OperationConstructDirectX:
data_address_ = ( // There are no direct, x instructions that access a two-byte value when
(registers_.direct & registers_.e_masks[0]) + // in emulation mode, so this can assume native mode.
((instruction_buffer_.value + registers_.direct + registers_.x.full) & registers_.e_masks[1])
) & 0xffff;
data_address_increment_mask_ = 0x00'ff'ff; data_address_increment_mask_ = 0x00'ff'ff;
incorrect_data_address_ = (registers_.direct & 0xff00) + (data_address_ & 0x00ff); // If the low byte of the direct register is 0, use the current e mask
// potentially to keep the high byte of the direct register unmodified.
//
// Also skip the next program step, which would be a redundant fetch
// from the program counter.
//
// Otherwise: retain a 16-bit address.
data_address_ = instruction_buffer_.value + registers_.direct + registers_.x.full;
if(!(registers_.direct&0xff)) { if(!(registers_.direct&0xff)) {
data_address_ =
(registers_.direct & registers_.e_masks[0]) |
(data_address_ & registers_.e_masks[1]);
++next_op_; ++next_op_;
} else {
data_address_ &= 0xffff;
} }
continue; continue;
case OperationConstructDirectY: case OperationConstructDirectY:
data_address_ = ( // Cf. comments above in DirectX.
(registers_.direct & registers_.e_masks[0]) +
((instruction_buffer_.value + registers_.direct + registers_.y.full) & registers_.e_masks[1])
) & 0xffff;
data_address_increment_mask_ = 0x00'ff'ff; data_address_increment_mask_ = 0x00'ff'ff;
data_address_ = instruction_buffer_.value + registers_.direct + registers_.y.full;
incorrect_data_address_ = (registers_.direct & 0xff00) + (data_address_ & 0x00ff);
if(!(registers_.direct&0xff)) { if(!(registers_.direct&0xff)) {
data_address_ =
(registers_.direct & registers_.e_masks[0]) |
(data_address_ & registers_.e_masks[1]);
++next_op_; ++next_op_;
} else {
data_address_ &= 0xffff;
} }
continue; continue;