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Pushes ahead to what will be my first interaction with the T flag.

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This commit is contained in:
Thomas Harte 2021-01-20 20:27:09 -05:00
parent 9f12ce2fb8
commit df1bc18fb3
2 changed files with 46 additions and 2 deletions
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46
InstructionSets/M50740/Executor.cpp
View File

@ -95,6 +95,27 @@ uint8_t Executor::pull() {
return read(s_);
}
void Executor::set_flags(uint8_t flags) {
negative_result_ = flags;
overflow_result_ = uint8_t(flags << 1);
index_mode_ = flags & 0x20;
decimal_mode_ = flags & 0x08;
interrupt_disable_ = flags & 0x04;
zero_result_ = !(flags & 0x02);
carry_flag_ = flags & 0x01;
}
uint8_t Executor::flags() {
return
(negative_result_ & 0x80) |
((overflow_result_ & 0x80) >> 1) |
(index_mode_ ? 0x20 : 0x00) |
(decimal_mode_ ? 0x08 : 0x00) |
interrupt_disable_ |
(zero_result_ ? 0x00 : 0x02) |
carry_flag_;
}
template <Operation operation, AddressingMode addressing_mode> void Executor::perform() {
// Deal with all modes that don't access memory up here;
// those that access memory will go through a slightly longer
@ -203,8 +224,12 @@ template <Operation operation, AddressingMode addressing_mode> void Executor::pe
case Operation::BMI: if(negative_result_&0x80) set_program_counter(uint16_t(address)); return;
case Operation::BEQ: if(!zero_result_) set_program_counter(uint16_t(address)); return;
case Operation::BNE: if(zero_result_) set_program_counter(uint16_t(address)); return;
case Operation::BCS: if(carry_flag_) set_program_counter(uint16_t(address)); return;
case Operation::BCC: if(!carry_flag_) set_program_counter(uint16_t(address)); return;
case Operation::BVS: if(overflow_result_ & 0x80) set_program_counter(uint16_t(address)); return;
case Operation::BVC: if(!(overflow_result_ & 0x80)) set_program_counter(uint16_t(address)); return;
/* TODO: all other types of branches. */
/* TODO: BBC, BBS. */
default: break;
}
@ -256,7 +281,7 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
break;
case Operation::CLI: interrupt_disable_ = 0x00; break;
case Operation::SEI: interrupt_disable_ = 0xff; break;
case Operation::SEI: interrupt_disable_ = 0x04; break;
case Operation::CLT: index_mode_ = false; break;
case Operation::SET: index_mode_ = true; break;
case Operation::CLD: decimal_mode_ = false; break;
@ -280,6 +305,23 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
// after exiting from here.
} break;
case Operation::RTI: {
set_flags(pull());
uint16_t target = pull();
target |= pull() << 8;
set_program_counter(target);
--program_counter_; // To undo the unavoidable increment
// after exiting from here.
} break;
case Operation::ORA: set_nz(a_ |= *operand); break;
case Operation::AND: set_nz(a_ &= *operand); break;
case Operation::EOR: set_nz(a_ ^= *operand); break;
/*
Operations affected by the index mode flag: ADC, AND, CMP, EOR, LDA, ORA, and SBC.
*/
/*
Already removed from the instruction stream:

2
InstructionSets/M50740/Executor.hpp
View File

@ -130,6 +130,8 @@ class Executor: public CachingExecutor {
inline void write(uint16_t address, uint8_t value);
inline void push(uint8_t value);
inline uint8_t pull();
inline void set_flags(uint8_t);
inline uint8_t flags();
};
}