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Merge pull request #1091 from TomHarte/65816DxDy

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Fix 65816 direct, [x/y] addressing when E=1, DL != 0.
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Thomas Harte 2022-09-09 16:57:10 -04:00 committed by GitHub
commit cb7f1e42ff
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2 changed files with 55 additions and 20 deletions
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38
Processors/65816/Implementation/65816Implementation.hpp
View File

@ -334,6 +334,7 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
case OperationConstructDirect:
data_address_ = (registers_.direct + instruction_buffer_.value) & 0xffff;
data_address_increment_mask_ = 0x00'ff'ff;
if(!(registers_.direct&0xff)) {
// If the low byte is 0 and this is emulation mode, incrementing
// is restricted to the low byte.
@ -345,6 +346,7 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
case OperationConstructDirectLong:
data_address_ = (registers_.direct + instruction_buffer_.value) & 0xffff;
data_address_increment_mask_ = 0x00'ff'ff;
if(!(registers_.direct&0xff)) {
++next_op_;
}
@ -380,31 +382,41 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
data_buffer_.clear();
continue;
// TODO: confirm incorrect_data_address_ below.
case OperationConstructDirectX:
data_address_ = (
(registers_.direct & registers_.e_masks[0]) +
((instruction_buffer_.value + registers_.direct + registers_.x.full) & registers_.e_masks[1])
) & 0xffff;
// There are no direct, x instructions that access a two-byte value when
// in emulation mode, so this can assume native mode.
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)) {
data_address_ =
(registers_.direct & registers_.e_masks[0]) |
(data_address_ & registers_.e_masks[1]);
++next_op_;
} else {
data_address_ &= 0xffff;
}
continue;
case OperationConstructDirectY:
data_address_ = (
(registers_.direct & registers_.e_masks[0]) +
((instruction_buffer_.value + registers_.direct + registers_.y.full) & registers_.e_masks[1])
) & 0xffff;
// Cf. comments above in DirectX.
data_address_increment_mask_ = 0x00'ff'ff;
incorrect_data_address_ = (registers_.direct & 0xff00) + (data_address_ & 0x00ff);
data_address_ = instruction_buffer_.value + registers_.direct + registers_.y.full;
if(!(registers_.direct&0xff)) {
data_address_ =
(registers_.direct & registers_.e_masks[0]) |
(data_address_ & registers_.e_masks[1]);
++next_op_;
} else {
data_address_ &= 0xffff;
}
continue;

37
Processors/65816/Implementation/65816Storage.hpp
View File

@ -281,13 +281,36 @@ struct ProcessorStorage {
// Flags aplenty.
MOS6502Esque::LazyFlags flags;
uint8_t mx_flags[2] = {1, 1}; // [0] = m; [1] = x. In both cases either `0` or `1`; `1` => 8-bit.
uint16_t m_masks[2] = {0xff00, 0x00ff}; // [0] = src mask (i.e. that which is unaffected by an operation); [1] = dst mask (i.e. 0xffff ^ src mask).
uint16_t x_mask = 0x00ff; // A mask representing the current size of the index registers. Equivalent to m_masks[1].
uint16_t e_masks[2] = {0xff00, 0x00ff}; // Akin to m_masks, but set as per emulation mode.
int m_shift = 0; // How far to shift memory/A to align its sign bit with that of the flags register. i.e. 8 for 16-bit mode, 0 for 8-bit mode.
int x_shift = 0; // m_shift equivalent for X and Y.
bool emulation_flag = true; // The emulation flag; true = in emulation mode.
// [0] = m; [1] = x. In both cases either `0` or `1`; `1` => 8-bit.
uint8_t mx_flags[2] = {1, 1};
// Used to determine which parts of a register are currently in use, as a function
// of the M flag.
//
// [0] = src mask (i.e. that which is unaffected by an operation);
// [1] = dst mask (i.e. 0xffff ^ src mask).
//
// e.g. a LDA from the value Q would prima facie leave A as equal to:
// (A & m_masks[0]) | (Q & m_masks[1]);
uint16_t m_masks[2] = {0xff00, 0x00ff};
// A mask representing the current size of the index registers.
// Equivalent in meaning to m_masks[1] but representative of the X flag.
uint16_t x_mask = 0x00ff;
// Akin to m_masks, but a function of emulation mode; used primarily for address calculation.
uint16_t e_masks[2] = {0xff00, 0x00ff};
// How far to shift memory/A to align its sign bit with that of the flags register.
// i.e. 8 for 16-bit mode, 0 for 8-bit mode.
int m_shift = 0;
// m_shift equivalent for X and Y.
int x_shift = 0;
// The emulation flag; true = in emulation mode.
bool emulation_flag = true;
// The offset for direct addressing (i.e. outside of emulation mode).
uint16_t direct = 0;