CLK/Machines/AtariST/DMAController.cpp

//
//  DMAController.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 26/10/2019.
//  Copyright © 2019 Thomas Harte. All rights reserved.
//

#include "DMAController.hpp"

#include <cstdio>

using namespace Atari::ST;

namespace {

enum Control: uint16_t {
	Direction = 0x100,
	DRQSource = 0x80,
	SectorCountSelect = 0x10,
	CPUTarget = 0x08
};

}

DMAController::DMAController() {
	fdc_.set_delegate(this);
	fdc_.set_clocking_hint_observer(this);
}

uint16_t DMAController::read(int address) {
	switch(address & 7) {
		// Reserved.
		default: break;

		// Disk controller or sector count.
		case 2:
			if(control_ & Control::SectorCountSelect) {
				return uint16_t((byte_count_ + 511) >> 9);	// Assumed here: the count is of sectors remaining, i.e. it decrements
															// only when a sector is complete.
			} else {
				if(control_ & Control::CPUTarget) {
					return 0xffff;
				} else {
					return 0xff00 | fdc_.get_register(control_ >> 1);
				}
			}
		break;

		// DMA status.
		case 3:
		// TODO: should DRQ come from the HDC if that mode is selected?
		return 0xfff8 | (error_ ? 0 : 1) | (byte_count_ ? 2 : 0) | (fdc_.get_data_request_line() ? 4 : 0);

		// DMA addressing.
		case 4:	return uint16_t(0xff00 | ((address_ >> 16) & 0xff));
		case 5:	return uint16_t(0xff00 | ((address_ >> 8) & 0xff));
		case 6:	return uint16_t(0xff00 | ((address_ >> 0) & 0xff));
	}
	return 0xffff;
}

void DMAController::write(int address, uint16_t value) {
	switch(address & 7) {
		// Reserved.
		default: break;

		// Disk controller or sector count.
		case 2:
			if(control_ & Control::SectorCountSelect) {
				byte_count_ = (value & 0xff) << 9;	// The computer provides a sector count; that times 512 is a byte count.

				// TODO: if this is a write-mode DMA operation, try to fill both buffers, ASAP.
			} else {
				if(control_ & Control::CPUTarget) {
					// TODO: HDC.
				} else {
					fdc_.set_register(control_ >> 1, uint8_t(value));
				}
			}
		break;

		// DMA control; meaning is:
		//
		//	b0: unused
		//	b1, b2 = address lines for FDC access.
		//	b3 = 1 => CPU HDC access; 0 => CPU FDC access.
		//	b4 = 1 => sector count access; 0 => [F/H]DC access.
		//	b5: unused.
		//	b6 = officially, 1 => DMA off; 0 => DMA on. Ignored in real hardware.
		//	b7 = 1 => FDC DRQs being observed; 0 => HDC access DRQs being observed.
		//	b8 = 1 => DMA is writing to [F/H]DC; 0 => DMA is reading. Changing value resets DMA state.
		//
		//	All other bits: undefined.
		case 3:
			// Check for a DMA state reset.
			if((control_^value) & Control::Direction) {
				bytes_received_ = active_buffer_ = 0;
				error_ = false;
				byte_count_ = 0;
			}
			control_ = value;
		break;

		// DMA addressing.
		case 4:	address_ = int((address_ & 0x00ffff) | ((value & 0xff) << 16));	break;
		case 5:	address_ = int((address_ & 0xff00ff) | ((value & 0xff) << 8));	break;
		case 6:	address_ = int((address_ & 0xffff00) | ((value & 0xff) << 0));	break;
	}
}

void DMAController::set_floppy_drive_selection(bool drive1, bool drive2, bool side2) {
	fdc_.set_floppy_drive_selection(drive1, drive2, side2);
}

void DMAController::set_floppy_disk(std::shared_ptr<Storage::Disk::Disk> disk, size_t drive) {
	fdc_.drives_[drive]->set_disk(disk);
}

void DMAController::run_for(HalfCycles duration) {
	running_time_ += duration;
	fdc_.run_for(duration.flush<Cycles>());
}

void DMAController::wd1770_did_change_output(WD::WD1770 *) {
	// Check for a change in interrupt state.
	const bool old_interrupt_line = interrupt_line_;
	interrupt_line_ = fdc_.get_interrupt_request_line();
	if(interrupt_delegate_ && interrupt_line_ != old_interrupt_line) {
		interrupt_delegate_->dma_controller_did_change_interrupt_status(this);
	}

	// Check for a change in DRQ state, if it's the FDC that is currently being watched.
	if(fdc_.get_data_request_line()) {
		if(!(control_ & Control::DRQSource)) return;
		if(control_ & Control::Direction) {
			// TODO: DMA is supposed to be helping with a write.
		} else {
			// DMA is enabling a read.

			// Read from the data register into the active buffer.
			buffer_[active_buffer_][bytes_received_] = fdc_.get_register(3);
			++bytes_received_;
			if(bytes_received_ == 16) {
				// TODO: BusReq and eventual deposit into RAM?

				active_buffer_ ^= 1;
				bytes_received_ = 0;
			}
		}
	}
}

void DMAController::set_interrupt_delegate(InterruptDelegate *delegate) {
	interrupt_delegate_ = delegate;
}

bool DMAController::get_interrupt_line() {
	return interrupt_line_;
}

void DMAController::set_component_prefers_clocking(ClockingHint::Source *, ClockingHint::Preference) {
	update_clocking_observer();
}

ClockingHint::Preference DMAController::preferred_clocking() {
	return (fdc_.preferred_clocking() == ClockingHint::Preference::None) ? ClockingHint::Preference::None : ClockingHint::Preference::RealTime;
}