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CLK/Processors/68000/Implementation/68000Implementation.hpp
Thomas Harte be4b38c76a Adds BRA and Bcc.
2019-03-25 22:54:49 -04:00

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//
// 68000Implementation.hpp
// Clock Signal
//
// Created by Thomas Harte on 10/03/2019.
// Copyright © 2019 Thomas Harte. All rights reserved.
//
#define get_status() \
( \
(carry_flag_ ? 0x0001 : 0x0000) | \
(overflow_flag_ ? 0x0002 : 0x0000) | \
(zero_result_ ? 0x0000 : 0x0004) | \
(negative_flag_ ? 0x0008 : 0x0000) | \
(extend_flag_ ? 0x0010 : 0x0000) | \
(interrupt_level_ << 8) | \
(trace_flag_ ? 0x8000 : 0x0000) | \
(is_supervisor_ << 13) \
)
#define set_status(x) \
carry_flag_ = (x) & 0x0001; \
overflow_flag_ = (x) & 0x0002; \
zero_result_ = ((x) & 0x0004) ^ 0x0004; \
negative_flag_ = (x) & 0x0008; \
extend_flag_ = (x) & 0x0010; \
interrupt_level_ = ((x) >> 8) & 7; \
trace_flag_ = (x) & 0x8000; \
is_supervisor_ = ((x) >> 13) & 1;
template <class T, bool dtack_is_implicit> void Processor<T, dtack_is_implicit>::run_for(HalfCycles duration) {
HalfCycles remaining_duration = duration + half_cycles_left_to_run_;
while(remaining_duration > HalfCycles(0)) {
/*
FIND THE NEXT MICRO-OP IF UNKNOWN.
*/
if(active_step_->is_terminal()) {
while(true) {
// If there are any more micro-operations available, just move onwards.
if(active_micro_op_ && !active_micro_op_->is_terminal()) {
++active_micro_op_;
} else {
// Either the micro-operations for this instruction have been exhausted, or
// no instruction was ongoing. Either way, do a standard instruction operation.
// TODO: unless an interrupt is pending, or the trap flag is set.
const uint16_t next_instruction = prefetch_queue_.halves.high.full;
if(!instructions[next_instruction].micro_operations) {
// TODO: once all instructions are implemnted, this should be an instruction error.
std::cerr << "68000 Abilities exhausted; can't manage instruction " << std::hex << next_instruction << std::endl;
return;
}
active_program_ = &instructions[next_instruction];
active_micro_op_ = active_program_->micro_operations;
}
switch(active_micro_op_->action) {
default:
std::cerr << "Unhandled 68000 micro op action " << std::hex << active_micro_op_->action << std::endl;
break;
case int(MicroOp::Action::None): break;
case int(MicroOp::Action::PerformOperation):
switch(active_program_->operation) {
/*
ABCD adds the lowest bytes form the source and destination using BCD arithmetic,
obeying the extend flag.
*/
case Operation::ABCD: {
// Pull out the two halves, for simplicity.
const uint8_t source = active_program_->source->halves.low.halves.low;
const uint8_t destination = active_program_->destination->halves.low.halves.low;
// Perform the BCD add by evaluating the two nibbles separately.
int result = (destination & 0xf) + (source & 0xf) + (extend_flag_ ? 1 : 0);
if(result > 0x09) result += 0x06;
result += (destination & 0xf0) + (source & 0xf0);
if(result > 0x99) result += 0x60;
// Set all flags essentially as if this were normal addition.
zero_result_ |= result & 0xff;
extend_flag_ = carry_flag_ = result & ~0xff;
negative_flag_ = result & 0x80;
overflow_flag_ = ~(source ^ destination) & (destination ^ result) & 0x80;
// Store the result.
active_program_->destination->halves.low.halves.low = uint8_t(result);
} break;
// BRA: alters the program counter, exclusively via the prefetch queue.
case Operation::BRA: {
const int8_t byte_offset = int8_t(prefetch_queue_.halves.high.halves.low);
// A non-zero offset byte branches by just that amount; otherwise use the word
// after as an offset. In both cases, treat as signed.
if(byte_offset) {
program_counter_.full = (program_counter_.full + byte_offset) - 2;
} else {
program_counter_.full += int16_t(prefetch_queue_.halves.low.full);
}
} break;
// Bcc: evaluates the relevant condition and displacement size and then:
// if condition is false, schedules bus operations to get past this instruction;
// otherwise applies the offset and schedules bus operations to refill the prefetch queue.
case Operation::Bcc: {
// Grab the 8-bit offset.
const int8_t byte_offset = int8_t(prefetch_queue_.halves.high.halves.low);
// Test the conditional.
bool should_branch;
switch(prefetch_queue_.halves.high.halves.high & 0xf) {
default:
case 0x00: should_branch = true; break; // true
case 0x01: should_branch = false; break; // false
case 0x02: should_branch = zero_result_ && !carry_flag_; break; // high
case 0x03: should_branch = !zero_result_ || carry_flag_; break; // low or same
case 0x04: should_branch = !carry_flag_; break; // carry clear
case 0x05: should_branch = carry_flag_; break; // carry set
case 0x06: should_branch = zero_result_; break; // not equal
case 0x07: should_branch = !zero_result_; break; // equal
case 0x08: should_branch = !overflow_flag_; break; // overflow clear
case 0x09: should_branch = overflow_flag_; break; // overflow set
case 0x0a: should_branch = !negative_flag_; break; // positive
case 0x0b: should_branch = negative_flag_; break; // negative
case 0x0c:
should_branch = (negative_flag_ && overflow_flag_) || (!negative_flag_ && !overflow_flag_);
break; // greater than or equal
case 0x0d:
should_branch = (negative_flag_ || !overflow_flag_) && (!negative_flag_ || overflow_flag_);
break; // less than
case 0x0e:
should_branch = zero_result_ && ((negative_flag_ && overflow_flag_) || (!negative_flag_ && !overflow_flag_));
break; // greater than
case 0x0f:
should_branch = (!zero_result_ || negative_flag_) && (!overflow_flag_ || !negative_flag_) && overflow_flag_;
break; // less than or equal
}
// Schedule something appropriate, by rewriting the program for this instruction temporarily.
if(should_branch) {
if(byte_offset) {
program_counter_.full = (program_counter_.full + byte_offset) - 2; // - 2 because this should be calculated from the high word of the prefetch.
} else {
program_counter_.full += int16_t(prefetch_queue_.halves.low.full);
}
active_micro_op_->bus_program = branch_taken_bus_steps_;
} else {
if(byte_offset) {
active_micro_op_->bus_program = branch_byte_not_taken_bus_steps_;
} else {
active_micro_op_->bus_program = branch_word_not_taken_bus_steps_;
}
}
} break;
/*
CMP.b, CMP.l and CMP.w: sets the condition flags (other than extend) based on a subtraction
of the source from the destination; the result of the subtraction is not stored.
*/
case Operation::CMPb: {
const uint8_t source = active_program_->source->halves.low.halves.low;
const uint8_t destination = active_program_->destination->halves.low.halves.low;
const int result = destination - source;
zero_result_ = result & 0xff;
carry_flag_ = result & ~0xff;
negative_flag_ = result & 0x80;
overflow_flag_ = (source ^ destination) & (destination ^ result) & 0x80;
} break;
case Operation::CMPw: {
const uint16_t source = active_program_->source->halves.low.full;
const uint16_t destination = active_program_->destination->halves.low.full;
const int result = destination - source;
zero_result_ = result & 0xffff;
carry_flag_ = result & ~0xffff;
negative_flag_ = result & 0x8000;
overflow_flag_ = (source ^ destination) & (destination ^ result) & 0x8000;
} break;
case Operation::CMPl: {
const uint32_t source = active_program_->source->full;
const uint32_t destination = active_program_->destination->full;
const uint64_t result = destination - source;
zero_result_ = uint32_t(result);
carry_flag_ = result >> 32;
negative_flag_ = result & 0x80000000;
overflow_flag_ = (source ^ destination) & (destination ^ result) & 0x80000000;
} break;
/*
MOVE.b, MOVE.l and MOVE.w: move the least significant byte or word, or the entire long word,
and set negative, zero, overflow and carry as appropriate.
*/
case Operation::MOVEb:
zero_result_ = active_program_->destination->halves.low.halves.low = active_program_->source->halves.low.halves.low;
negative_flag_ = zero_result_ & 0x80;
overflow_flag_ = carry_flag_ = 0;
break;
case Operation::MOVEw:
zero_result_ = active_program_->destination->halves.low.full = active_program_->source->halves.low.full;
negative_flag_ = zero_result_ & 0x8000;
overflow_flag_ = carry_flag_ = 0;
break;
case Operation::MOVEl:
zero_result_ = active_program_->destination->full = active_program_->source->full;
negative_flag_ = zero_result_ & 0x80000000;
overflow_flag_ = carry_flag_ = 0;
break;
/*
MOVEA.l: move the entire long word;
MOVEA.w: move the least significant word and sign extend it.
Neither sets any flags.
*/
case Operation::MOVEAw:
active_program_->destination->halves.low.full = active_program_->source->halves.low.full;
active_program_->destination->halves.high.full = (active_program_->destination->halves.low.full & 0x8000) ? 0xffff : 0;
break;
case Operation::MOVEAl:
active_program_->destination->full = active_program_->source->full;
break;
/*
Status word moves.
*/
case Operation::MOVEtoSR:
set_status(active_program_->source->full);
break;
case Operation::MOVEfromSR:
active_program_->source->halves.low.full = get_status();
break;
/*
SBCD subtracts the lowest byte of the source from that of the destination using
BCD arithmetic, obeying the extend flag.
*/
case Operation::SBCD: {
// Pull out the two halves, for simplicity.
const uint8_t source = active_program_->source->halves.low.halves.low;
const uint8_t destination = active_program_->destination->halves.low.halves.low;
// Perform the BCD add by evaluating the two nibbles separately.
int result = (destination & 0xf) - (source & 0xf) - (extend_flag_ ? 1 : 0);
if(result > 0x09) result -= 0x06;
result += (destination & 0xf0) - (source & 0xf0);
if(result > 0x99) result -= 0x60;
// Set all flags essentially as if this were normal subtraction.
zero_result_ |= result & 0xff;
extend_flag_ = carry_flag_ = result & ~0xff;
negative_flag_ = result & 0x80;
overflow_flag_ = (source ^ destination) & (destination ^ result) & 0x80;
// Store the result.
active_program_->destination->halves.low.halves.low = uint8_t(result);
} break;
/*
Development period debugging.
*/
default:
std::cerr << "Should do something with program operation " << int(active_program_->operation) << std::endl;
break;
}
break;
case int(MicroOp::Action::SetMoveFlagsb):
zero_result_ = active_program_->source->halves.low.halves.low;
negative_flag_ = zero_result_ & 0x80;
overflow_flag_ = carry_flag_ = 0;
break;
case int(MicroOp::Action::SetMoveFlagsw):
zero_result_ = active_program_->source->halves.low.full;
negative_flag_ = zero_result_ & 0x8000;
overflow_flag_ = carry_flag_ = 0;
break;
case int(MicroOp::Action::SetMoveFlagsl):
zero_result_ = active_program_->source->full;
negative_flag_ = zero_result_ & 0x80000000;
overflow_flag_ = carry_flag_ = 0;
break;
case int(MicroOp::Action::Decrement1):
if(active_micro_op_->action & MicroOp::SourceMask) active_program_->source->full -= 1;
if(active_micro_op_->action & MicroOp::DestinationMask) active_program_->destination->full -= 1;
break;
case int(MicroOp::Action::Decrement2):
if(active_micro_op_->action & MicroOp::SourceMask) active_program_->source->full -= 2;
if(active_micro_op_->action & MicroOp::DestinationMask) active_program_->destination->full -= 2;
break;
case int(MicroOp::Action::Decrement4):
if(active_micro_op_->action & MicroOp::SourceMask) active_program_->source->full -= 4;
if(active_micro_op_->action & MicroOp::DestinationMask) active_program_->destination->full -= 4;
break;
case int(MicroOp::Action::Increment1):
if(active_micro_op_->action & MicroOp::SourceMask) active_program_->source->full += 1;
if(active_micro_op_->action & MicroOp::DestinationMask) active_program_->destination->full += 1;
break;
case int(MicroOp::Action::Increment2):
if(active_micro_op_->action & MicroOp::SourceMask) active_program_->source->full += 2;
if(active_micro_op_->action & MicroOp::DestinationMask) active_program_->destination->full += 2;
break;
case int(MicroOp::Action::Increment4):
if(active_micro_op_->action & MicroOp::SourceMask) active_program_->source->full += 4;
if(active_micro_op_->action & MicroOp::DestinationMask) active_program_->destination->full += 4;
break;
case int(MicroOp::Action::SignExtendWord):
if(active_micro_op_->action & MicroOp::SourceMask) {
active_program_->source->halves.high.full =
(active_program_->source->halves.low.full & 0x8000) ? 0xffff : 0x0000;
}
if(active_micro_op_->action & MicroOp::DestinationMask) {
active_program_->destination->halves.high.full =
(active_program_->destination->halves.low.full & 0x8000) ? 0xffff : 0x0000;
}
break;
case int(MicroOp::Action::SignExtendByte):
if(active_micro_op_->action & MicroOp::SourceMask) {
active_program_->source->full = (active_program_->source->full & 0xff) |
(active_program_->source->full & 0x80) ? 0xffffff : 0x000000;
}
if(active_micro_op_->action & MicroOp::DestinationMask) {
active_program_->destination->full = (active_program_->destination->full & 0xff) |
(active_program_->destination->full & 0x80) ? 0xffffff : 0x000000;
}
break;
case int(MicroOp::Action::CalcD16An) | MicroOp::SourceMask:
effective_address_[0] = int16_t(prefetch_queue_.halves.low.full) + active_program_->source->full;
break;
case int(MicroOp::Action::CalcD16An) | MicroOp::DestinationMask:
effective_address_[1] = int16_t(prefetch_queue_.halves.low.full) + active_program_->destination->full;
break;
case int(MicroOp::Action::CalcD16An) | MicroOp::SourceMask | MicroOp::DestinationMask:
effective_address_[0] = int16_t(prefetch_queue_.halves.high.full) + active_program_->source->full;
effective_address_[1] = int16_t(prefetch_queue_.halves.low.full) + active_program_->destination->full;
break;
// TODO: permit as below for DestinationMask and SourceMask|DestinationMask; would prefer to test first.
#define CalculateD8AnXn(data, source, target) {\
const auto register_index = (data.full >> 12) & 7; \
const RegisterPair32 &displacement = (data.full & 0x8000) ? address_[register_index] : data_[register_index]; \
target = int8_t(data.halves.low) + source->full; \
\
if(data.full & 0x800) { \
effective_address_[0] += displacement.halves.low.full; \
} else { \
effective_address_[0] += displacement.full; \
} \
}
case int(MicroOp::Action::CalcD8AnXn) | MicroOp::SourceMask: {
CalculateD8AnXn(prefetch_queue_.halves.low, active_program_->source, effective_address_[0]);
} break;
case int(MicroOp::Action::CalcD8AnXn) | MicroOp::DestinationMask: {
CalculateD8AnXn(prefetch_queue_.halves.low, active_program_->destination, effective_address_[1]);
} break;
case int(MicroOp::Action::CalcD8AnXn) | MicroOp::SourceMask | MicroOp::DestinationMask: {
CalculateD8AnXn(prefetch_queue_.halves.high, active_program_->source, effective_address_[0]);
CalculateD8AnXn(prefetch_queue_.halves.low, active_program_->destination, effective_address_[1]);
} break;
#undef CalculateD8AnXn
case int(MicroOp::Action::AssembleWordAddressFromPrefetch) | MicroOp::SourceMask:
// Assumption: this will be assembling right at the start of the instruction.
effective_address_[0] = prefetch_queue_.halves.low.full;
break;
case int(MicroOp::Action::AssembleWordAddressFromPrefetch) | MicroOp::DestinationMask:
effective_address_[1] = prefetch_queue_.halves.low.full;
break;
case int(MicroOp::Action::AssembleLongWordAddressFromPrefetch) | MicroOp::SourceMask:
effective_address_[0] = prefetch_queue_.full;
break;
case int(MicroOp::Action::AssembleLongWordAddressFromPrefetch) | MicroOp::DestinationMask:
effective_address_[1] = prefetch_queue_.full;
break;
case int(MicroOp::Action::AssembleWordDataFromPrefetch) | MicroOp::SourceMask:
// Assumption: this will be assembling right at the start of the instruction.
bus_data_[0] = prefetch_queue_.halves.low.full;
break;
case int(MicroOp::Action::AssembleWordDataFromPrefetch) | MicroOp::DestinationMask:
bus_data_[1] = prefetch_queue_.halves.low.full;
break;
case int(MicroOp::Action::AssembleLongWordDataFromPrefetch) | MicroOp::SourceMask:
bus_data_[0] = prefetch_queue_.full;
break;
case int(MicroOp::Action::AssembleLongWordDataFromPrefetch) | MicroOp::DestinationMask:
bus_data_[1] = prefetch_queue_.full;
break;
}
// If we've got to a micro-op that includes bus steps, break out of this loop.
if(!active_micro_op_->is_terminal()) {
active_step_ = active_micro_op_->bus_program;
break;
}
}
}
/*
PERFORM THE CURRENT BUS STEP'S MICROCYCLE.
*/
// Check for DTack if this isn't being treated implicitly.
if(!dtack_is_implicit) {
if(active_step_->microcycle.data_select_active() && !dtack_) {
// TODO: perform wait state.
continue;
}
}
// TODO: synchronous bus.
// TODO: check for bus error.
// Perform the microcycle.
remaining_duration -=
active_step_->microcycle.length +
bus_handler_.perform_bus_operation(active_step_->microcycle, is_supervisor_);
/*
PERFORM THE BUS STEP'S ACTION.
*/
switch(active_step_->action) {
default:
std::cerr << "Unimplemented 68000 bus step action: " << int(active_step_->action) << std::endl;
return;
break;
case BusStep::Action::None: break;
case BusStep::Action::IncrementEffectiveAddress0: effective_address_[0] += 2; break;
case BusStep::Action::IncrementEffectiveAddress1: effective_address_[1] += 2; break;
case BusStep::Action::IncrementProgramCounter: program_counter_.full += 2; break;
case BusStep::Action::AdvancePrefetch:
prefetch_queue_.halves.high = prefetch_queue_.halves.low;
break;
}
// Move to the next bus step.
++ active_step_;
}
half_cycles_left_to_run_ = remaining_duration;
}
template <class T, bool dtack_is_implicit> ProcessorState Processor<T, dtack_is_implicit>::get_state() {
write_back_stack_pointer();
State state;
memcpy(state.data, data_, sizeof(state.data));
memcpy(state.address, address_, sizeof(state.address));
state.user_stack_pointer = stack_pointers_[0].full;
state.supervisor_stack_pointer = stack_pointers_[1].full;
state.status = get_status();
return state;
}
template <class T, bool dtack_is_implicit> void Processor<T, dtack_is_implicit>::set_state(const ProcessorState &state) {
memcpy(data_, state.data, sizeof(state.data));
memcpy(address_, state.address, sizeof(state.address));
stack_pointers_[0].full = state.user_stack_pointer;
stack_pointers_[1].full = state.supervisor_stack_pointer;
set_status(state.status);
address_[7] = stack_pointers_[is_supervisor_];
}
#undef get_status
#undef set_status
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