mirror of
https://github.com/TomHarte/CLK.git
synced 2024-08-16 16:28:59 +00:00
144 lines
3.7 KiB
C++
144 lines
3.7 KiB
C++
//
|
||
// Copper.cpp
|
||
// Clock Signal
|
||
//
|
||
// Created by Thomas Harte on 16/09/2021.
|
||
// Copyright © 2021 Thomas Harte. All rights reserved.
|
||
//
|
||
|
||
#ifndef NDEBUG
|
||
#define NDEBUG
|
||
#endif
|
||
|
||
#define LOG_PREFIX "[Copper] "
|
||
#include "../../Outputs/Log.hpp"
|
||
|
||
#include "Chipset.hpp"
|
||
#include "Copper.hpp"
|
||
|
||
using namespace Amiga;
|
||
|
||
namespace {
|
||
|
||
bool satisfies_raster(uint16_t position, uint16_t blitter_status, uint16_t *instruction) {
|
||
const uint16_t mask = 0x8000 | (instruction[1] & 0x7ffe);
|
||
return
|
||
(position & mask) >= (instruction[0] & mask) &&
|
||
(!(blitter_status & 0x4000) || (instruction[1] & 0x8000));
|
||
}
|
||
|
||
}
|
||
|
||
//
|
||
// Quick notes on the Copper:
|
||
//
|
||
// There are three instructions: move, wait and skip. All are two words in length.
|
||
//
|
||
// Move writes a value to one of the Chipset registers; it is encoded as:
|
||
//
|
||
// First word:
|
||
// b0: 0
|
||
// b1–b8: register address
|
||
// b9+: unused ("should be set to 0")
|
||
//
|
||
// Second word:
|
||
// b0–b15: value to move.
|
||
//
|
||
//
|
||
// Wait waits until the raster gets to at least a certain position, and
|
||
// optionally until the Blitter has finished. It is encoded as:
|
||
//
|
||
// First word:
|
||
// b0: 1
|
||
// b1–b7: horizontal beam position
|
||
// b8+: vertical beam position
|
||
//
|
||
// Second word:
|
||
// b0: 0
|
||
// b1–b7: horizontal beam comparison mask
|
||
// b8–b14: vertical beam comparison mask
|
||
// b15: 1 => don't also wait for the Blitter to be finished; 0 => wait.
|
||
//
|
||
//
|
||
// Skip skips the next instruction if the raster has already reached a certain
|
||
// position, and optionally only if the Blitter has finished, and only if the
|
||
// next instruction is a move.
|
||
//
|
||
// First word:
|
||
// b0: 1
|
||
// b1–b7: horizontal beam position
|
||
// b8+: vertical beam position
|
||
//
|
||
// Second word:
|
||
// b0: 1
|
||
// b1–b7: horizontal beam comparison mask
|
||
// b8–b14: vertical beam comparison mask
|
||
// b15: 1 => don't also test whether the Blitter is finished; 0 => test.
|
||
//
|
||
bool Copper::advance_dma(uint16_t position, uint16_t blitter_status) {
|
||
switch(state_) {
|
||
default: return false;
|
||
|
||
case State::Waiting:
|
||
if(satisfies_raster(position, blitter_status, instruction_)) {
|
||
LOG("Unblocked waiting for " << PADHEX(4) << instruction_[0] << " at " << PADHEX(4) << position << " with mask " << PADHEX(4) << (instruction_[1] & 0x7ffe));
|
||
state_ = State::FetchFirstWord;
|
||
}
|
||
return false;
|
||
|
||
case State::FetchFirstWord:
|
||
instruction_[0] = ram_[address_ & ram_mask_];
|
||
++address_;
|
||
state_ = State::FetchSecondWord;
|
||
LOG("First word fetch at " << PADHEX(4) << position);
|
||
break;
|
||
|
||
case State::FetchSecondWord: {
|
||
// Get and reset the should-skip-next flag.
|
||
const bool should_skip_move = skip_next_;
|
||
skip_next_ = false;
|
||
|
||
// Read in the second instruction word.
|
||
instruction_[1] = ram_[address_ & ram_mask_];
|
||
++address_;
|
||
LOG("Second word fetch at " << PADHEX(4) << position);
|
||
|
||
// Check for a MOVE.
|
||
if(!(instruction_[0] & 1)) {
|
||
if(!should_skip_move) {
|
||
// Stop if this move would be a privilege violation.
|
||
instruction_[0] &= 0x1fe;
|
||
if((instruction_[0] < 0x10) || (instruction_[0] < 0x20 && !(control_&1))) {
|
||
LOG("Invalid MOVE to " << PADHEX(4) << instruction_[0] << "; stopping");
|
||
state_ = State::Stopped;
|
||
break;
|
||
}
|
||
|
||
chipset_.write(instruction_[0], instruction_[1]);
|
||
}
|
||
|
||
// Roll onto the next command.
|
||
state_ = State::FetchFirstWord;
|
||
break;
|
||
}
|
||
|
||
// Got to here => this is a WAIT or a SKIP.
|
||
|
||
if(!(instruction_[1] & 1)) {
|
||
// A WAIT. The wait-for-start-of-next PAL wait of
|
||
// $FFDF,$FFFE seems to suggest evaluation will happen
|
||
// in the next cycle rather than this one.
|
||
state_ = State::Waiting;
|
||
break;
|
||
}
|
||
|
||
// Neither a WAIT nor a MOVE => a SKIP.
|
||
|
||
skip_next_ = satisfies_raster(position, blitter_status, instruction_);
|
||
state_ = State::FetchFirstWord;
|
||
} break;
|
||
}
|
||
|
||
return true;
|
||
}
|