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CLK/Machines/Amiga/BlitterSequencer.hpp

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2022-08-19 20:38:15 +00:00
//
// BlitterSequencer.hpp
// Clock Signal
//
// Created by Thomas Harte on 19/08/2022.
// Copyright © 2022 Thomas Harte. All rights reserved.
//
#ifndef BlitterSequencer_hpp
#define BlitterSequencer_hpp
#include <array>
namespace Amiga {
/*!
Statefully provides the next access the Blitter should make.
TODO: determine the actual logic here, rather than
relying on tables.
*/
class BlitterSequencer {
public:
enum class Channel {
/// Tells the caller to calculate and load a new piece of output
/// into the output pipeline.
///
/// If any inputs are enabled then a one-slot output pipeline applies:
/// output will rest in the pipeline for one write phase before being written.
Write,
/// Indicates that a write should occur if anything is in the pipeline, otherwise
/// no activity should occur.
FlushPipeline,
/// The caller should read from channel C.
C,
/// The caller should read from channel B.
B,
/// The caller should read from channel A.
A,
/// Indicates an unused DMA slot.
None
};
/// Sets the current control value, which indicates which
/// channels are enabled.
void set_control(int control) {
control_ = control & 0xf;
index_ = 0; // TODO: this probably isn't accurate; case caught is a change
// of control values during a blit.
}
/// Indicates that blitting should conclude after this step, i.e.
/// whatever is being fetched now is part of the final set of input data;
/// this is safe to call following a fetch request on any channel.
void complete() {
next_phase_ =
(control_ == 0x9 || control_ == 0xb || control_ == 0xd) ?
Phase::PauseAndComplete : Phase::Complete;
}
/// Begins a blit operation.
void begin() {
phase_ = next_phase_ = Phase::Ongoing;
index_ = loop_ = 0;
}
/// Provides the next channel to fetch from, or that a write is required,
/// along with a count of complete channel iterations so far completed.
std::pair<Channel, int> next() {
switch(phase_) {
default: break;
case Phase::Complete:
return std::make_pair(Channel::FlushPipeline, loop_);
case Phase::PauseAndComplete:
phase_ = Phase::Complete;
return std::make_pair(Channel::None, loop_);
}
Channel next = Channel::None;
switch(control_) {
default: break;
case 0: next = next_channel(pattern0); break;
case 1: next = next_channel(pattern1); break;
case 2: next = next_channel(pattern2); break;
case 3: next = next_channel(pattern3); break;
case 4: next = next_channel(pattern4); break;
case 5: next = next_channel(pattern5); break;
case 6: next = next_channel(pattern6); break;
case 7: next = next_channel(pattern7); break;
case 8: next = next_channel(pattern8); break;
case 9: next = next_channel(pattern9); break;
case 10: next = next_channel(patternA); break;
case 11: next = next_channel(patternB); break;
case 12: next = next_channel(patternC); break;
case 13: next = next_channel(patternD); break;
case 14: next = next_channel(patternE); break;
case 15: next = next_channel(patternF); break;
}
return std::make_pair(next, loop_);
}
template <int channel> bool channel_enabled() {
return control_ & (8 >> channel);
}
private:
static constexpr std::array<Channel, 1> pattern0 = { Channel::None };
static constexpr std::array<Channel, 2> pattern1 = { Channel::Write, Channel::None };
static constexpr std::array<Channel, 2> pattern2 = { Channel::C, Channel::None };
static constexpr std::array<Channel, 3> pattern3 = { Channel::C, Channel::Write, Channel::None };
static constexpr std::array<Channel, 3> pattern4 = { Channel::B, Channel::None, Channel::None };
static constexpr std::array<Channel, 3> pattern5 = { Channel::B, Channel::Write, Channel::None };
static constexpr std::array<Channel, 3> pattern6 = { Channel::B, Channel::C, Channel::None };
static constexpr std::array<Channel, 4> pattern7 = { Channel::B, Channel::C, Channel::Write, Channel::None };
static constexpr std::array<Channel, 2> pattern8 = { Channel::A, Channel::None };
static constexpr std::array<Channel, 2> pattern9 = { Channel::A, Channel::Write };
static constexpr std::array<Channel, 2> patternA = { Channel::A, Channel::C };
static constexpr std::array<Channel, 3> patternB = { Channel::A, Channel::C, Channel::Write };
static constexpr std::array<Channel, 3> patternC = { Channel::A, Channel::B, Channel::None };
static constexpr std::array<Channel, 3> patternD = { Channel::A, Channel::B, Channel::Write };
static constexpr std::array<Channel, 3> patternE = { Channel::A, Channel::B, Channel::C };
static constexpr std::array<Channel, 4> patternF = { Channel::A, Channel::B, Channel::C, Channel::Write };
template <typename ArrayT> Channel next_channel(const ArrayT &list) {
loop_ += index_ / list.size();
index_ %= list.size();
const Channel result = list[index_];
++index_;
if(index_ == list.size()) {
phase_ = next_phase_;
}
return result;
}
// Current control flags, i.e. which channels are enabled.
int control_ = 0;
// Index into the pattern table for this blit.
size_t index_ = 0;
// Number of times the entire pattern table has been completed.
int loop_ = 0;
enum class Phase {
/// Return the next thing in the pattern table and advance.
/// If looping from the end of the pattern table to the start,
/// set phase_ to next_phase_.
Ongoing,
/// Return a Channel::None and advancce to phase_ = Phase::Complete.
PauseAndComplete,
/// Return Channel::Write indefinitely.
Complete
};
// Current sequencer pahse.
Phase phase_ = Phase::Complete;
// Phase to assume at the end of this iteration of the sequence table.
Phase next_phase_ = Phase::Complete;
};
}
#endif /* BlitterSequencer_hpp */