mirror of
https://github.com/TomHarte/CLK.git
synced 2024-11-23 18:31:53 +00:00
130 lines
4.3 KiB
C++
130 lines
4.3 KiB
C++
//
|
||
// Status.hpp
|
||
// Clock Signal
|
||
//
|
||
// Created by Thomas Harte on 28/04/2022.
|
||
// Copyright © 2022 Thomas Harte. All rights reserved.
|
||
//
|
||
|
||
#ifndef InstructionSets_M68k_Status_h
|
||
#define InstructionSets_M68k_Status_h
|
||
|
||
#include "Instruction.hpp"
|
||
|
||
namespace InstructionSet {
|
||
namespace M68k {
|
||
|
||
namespace ConditionCode {
|
||
|
||
static constexpr uint16_t Carry = 1 << 0;
|
||
static constexpr uint16_t Overflow = 1 << 1;
|
||
static constexpr uint16_t Zero = 1 << 2;
|
||
static constexpr uint16_t Negative = 1 << 3;
|
||
static constexpr uint16_t Extend = 1 << 4;
|
||
|
||
static constexpr uint16_t AllConditions = Carry | Overflow | Zero | Negative | Extend;
|
||
|
||
static constexpr uint16_t Supervisor = 1 << 13;
|
||
static constexpr uint16_t Trace = 1 << 15;
|
||
|
||
static constexpr uint16_t InterruptPriorityMask = 0b111 << 8;
|
||
|
||
}
|
||
|
||
|
||
struct Status {
|
||
/// Generally holds an unevaluated flag for potential later lazy evaluation; it'll be zero for one outcome,
|
||
/// non-zero for the other, but no guarantees are made about the potential range of non-zero values.
|
||
using FlagT = uint_fast32_t;
|
||
|
||
/* b15 */
|
||
FlagT trace_flag = 0; // The trace flag is set if and only if this value is non-zero.
|
||
|
||
/* b13 */
|
||
bool is_supervisor = false; // true => processor is in supervisor mode; false => it isn't.
|
||
|
||
/* b7–b9 */
|
||
int interrupt_level = 0; // The direct integer value of the current interrupt level.
|
||
// Values of 8 or greater have undefined meaning.
|
||
|
||
/* b0–b4 */
|
||
FlagT zero_result = 0; // The zero flag is set if and only if this value is zero.
|
||
FlagT carry_flag = 0; // The carry flag is set if and only if this value is non-zero.
|
||
FlagT extend_flag = 0; // The extend flag is set if and only if this value is non-zero.
|
||
FlagT overflow_flag = 0; // The overflow flag is set if and only if this value is non-zero.
|
||
FlagT negative_flag = 0; // The negative flag is set if and only this value is non-zero.
|
||
|
||
/// Gets the current condition codes.
|
||
constexpr uint16_t ccr() const {
|
||
return
|
||
(carry_flag ? ConditionCode::Carry : 0) |
|
||
(overflow_flag ? ConditionCode::Overflow : 0) |
|
||
(!zero_result ? ConditionCode::Zero : 0) |
|
||
(negative_flag ? ConditionCode::Negative : 0) |
|
||
(extend_flag ? ConditionCode::Extend : 0);
|
||
}
|
||
|
||
/// Sets the current condition codes.
|
||
constexpr void set_ccr(uint16_t ccr) {
|
||
carry_flag = ccr & ConditionCode::Carry;
|
||
overflow_flag = ccr & ConditionCode::Overflow;
|
||
zero_result = ~ccr & ConditionCode::Zero;
|
||
negative_flag = ccr & ConditionCode::Negative;
|
||
extend_flag = ccr & ConditionCode::Extend;
|
||
}
|
||
|
||
/// Gets the current value of the status register.
|
||
constexpr uint16_t status() const {
|
||
return uint16_t(
|
||
ccr() |
|
||
(interrupt_level << 8) |
|
||
(trace_flag ? ConditionCode::Trace : 0) |
|
||
(is_supervisor ? ConditionCode::Supervisor : 0)
|
||
);
|
||
}
|
||
|
||
/// Sets the current value of the status register;
|
||
/// @returns @c true if the processor finishes in supervisor mode; @c false otherwise.
|
||
constexpr bool set_status(uint16_t status) {
|
||
set_ccr(status);
|
||
|
||
interrupt_level = (status >> 8) & 7;
|
||
trace_flag = status & ConditionCode::Trace;
|
||
is_supervisor = status & ConditionCode::Supervisor;
|
||
|
||
return is_supervisor;
|
||
}
|
||
|
||
/// Evaluates @c condition.
|
||
bool evaluate_condition(Condition condition) {
|
||
switch(condition) {
|
||
default:
|
||
case Condition::True: return true;
|
||
case Condition::False: return false;
|
||
case Condition::High: return zero_result && !carry_flag;
|
||
case Condition::LowOrSame: return !zero_result || carry_flag;
|
||
case Condition::CarryClear: return !carry_flag;
|
||
case Condition::CarrySet: return carry_flag;
|
||
case Condition::NotEqual: return zero_result;
|
||
case Condition::Equal: return !zero_result;
|
||
case Condition::OverflowClear: return !overflow_flag;
|
||
case Condition::OverflowSet: return overflow_flag;
|
||
case Condition::Positive: return !negative_flag;
|
||
case Condition::Negative: return negative_flag;
|
||
case Condition::GreaterThanOrEqual:
|
||
return (negative_flag && overflow_flag) || (!negative_flag && !overflow_flag);
|
||
case Condition::LessThan:
|
||
return (negative_flag && !overflow_flag) || (!negative_flag && overflow_flag);
|
||
case Condition::GreaterThan:
|
||
return zero_result && ((negative_flag && overflow_flag) || (!negative_flag && !overflow_flag));
|
||
case Condition::LessThanOrEqual:
|
||
return !zero_result || (negative_flag && !overflow_flag) || (!negative_flag && overflow_flag);
|
||
}
|
||
}
|
||
};
|
||
|
||
}
|
||
}
|
||
|
||
#endif /* InstructionSets_M68k_Status_h */
|