CLK/Components/8272/i8272.cpp

//
//  i8272.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 05/08/2017.
//  Copyright © 2017 Thomas Harte. All rights reserved.
//

#include "i8272.hpp"

#include <cstdio>

using namespace Intel;

namespace {
const uint8_t StatusRQM = 0x80;	// Set: ready to send or receive from processor.
const uint8_t StatusDIO = 0x40;	// Set: data is expected to be taken from the 8272 by the processor.
const uint8_t StatusNDM = 0x20;	// Set: the execution phase of a data transfer command is ongoing and DMA mode is disabled.
const uint8_t StatusCB = 0x10;	// Set: the FDC is busy.
//const uint8_t StatusD3B = 0x08;	// Set: drive 3 is seeking.
//const uint8_t StatusD2B = 0x04;	// Set: drive 2 is seeking.
//const uint8_t StatusD1B = 0x02;	// Set: drive 1 is seeking.
//const uint8_t StatusD0B = 0x01;	// Set: drive 0 is seeking.
}

i8272::i8272(Cycles clock_rate, int clock_rate_multiplier, int revolutions_per_minute) :
	Storage::Disk::MFMController(clock_rate, clock_rate_multiplier, revolutions_per_minute),
	main_status_(StatusRQM),
	interesting_event_mask_((int)Event8272::CommandByte),
	resume_point_(0),
	delay_time_(0),
	status_{0, 0, 0} {
	posit_event((int)Event8272::CommandByte);
}

void i8272::run_for(Cycles cycles) {
	Storage::Disk::MFMController::run_for(cycles);

	// check for an expired timer
	if(delay_time_ > 0) {
		if(cycles.as_int() >= delay_time_) {
			delay_time_ = 0;
			posit_event((int)Event8272::Timer);
		} else {
			delay_time_ -= cycles.as_int();
		}
	}

	// update seek status of any drives presently seeking
	for(int c = 0; c < 4; c++) {
		if(drives_[c].phase == Drive::Seeking) {
			drives_[c].step_rate_counter += cycles.as_int();
			int steps = drives_[c].step_rate_counter / (8000 * step_rate_time_);
			drives_[c].step_rate_counter %= (8000 * step_rate_time_);
			while(steps--) {
				// Perform a step.
				int direction = (drives_[c].target_head_position < drives_[c].head_position) ? -1 : 1;
				drives_[c].drive->step(direction);
				drives_[c].head_position += direction;

				// Check for completion.
				if(seek_is_satisfied(c)) {
					drives_[c].phase = Drive::CompletedSeeking;
					if(drives_[c].target_head_position == -1) drives_[c].head_position = 0;
					break;
				}
			}
		}
	}
}

void i8272::set_register(int address, uint8_t value) {
	// don't consider attempted sets to the status register
	if(!address) return;

	// if not ready for commands, do nothing
	if(!(main_status_ & StatusRQM)) return;

	// accumulate latest byte in the command byte sequence
	command_.push_back(value);
	posit_event((int)Event8272::CommandByte);
}

uint8_t i8272::get_register(int address) {
	if(address) {
//		printf("8272 get data\n");

		if(result_stack_.empty()) return 0xff;
		uint8_t result = result_stack_.back();
		result_stack_.pop_back();
		if(result_stack_.empty()) posit_event((int)Event8272::ResultEmpty);

		return result;
	} else {
//		printf("Main status: %02x\n", main_status_);
		return main_status_;
	}
}

void i8272::set_disk(std::shared_ptr<Storage::Disk::Disk> disk, int drive) {
	if(drive < 4 && drive >= 0) {
		drives_[drive].drive->set_disk(disk);
	}
}

#define BEGIN_SECTION()	switch(resume_point_) { default:
#define END_SECTION()	}

#define WAIT_FOR_EVENT(mask)	resume_point_ = __LINE__; interesting_event_mask_ = (int)mask; return; case __LINE__:

#define PASTE(x, y) x##y
#define CONCAT(x, y) PASTE(x, y)

#define FIND_HEADER()	\
	CONCAT(find_header, __LINE__): WAIT_FOR_EVENT((int)Event::Token | (int)Event::IndexHole); \
	if(event_type == (int)Event::IndexHole) index_hole_limit_--;	\
	else if(get_latest_token().type == Token::ID) goto CONCAT(header_found, __LINE__);	\
	\
	if(index_hole_limit_) goto CONCAT(find_header, __LINE__);	\
	CONCAT(header_found, __LINE__):	0;\

#define FIND_DATA()	\
	CONCAT(find_data, __LINE__): WAIT_FOR_EVENT((int)Event::Token | (int)Event::IndexHole); \
	if(event_type == (int)Event::Token && get_latest_token().type != Token::Data) goto CONCAT(find_data, __LINE__);

#define READ_HEADER()	\
	distance_into_section_ = 0;	\
	set_data_mode(Reading);	\
	CONCAT(read_header, __LINE__): WAIT_FOR_EVENT(Event::Token); \
	header_[distance_into_section_] = get_latest_token().byte_value;	\
	distance_into_section_++; \
	if(distance_into_section_ != 7) goto CONCAT(read_header, __LINE__);	\
	set_data_mode(Scanning);

#define SET_DRIVE_HEAD_MFM()	\
	if(!dma_mode_) main_status_ |= StatusNDM;	\
	set_drive(drives_[command_[1]&3].drive);	\
	set_is_double_density(command_[0] & 0x40);

void i8272::posit_event(int event_type) {
	if(!(interesting_event_mask_ & event_type)) return;
	interesting_event_mask_ &= ~event_type;

	BEGIN_SECTION();

	// Resets busy and non-DMA execution, clears the command buffer, sets the data mode to scanning and flows
	// into wait_for_complete_command_sequence.
	wait_for_command:
			set_data_mode(Storage::Disk::MFMController::DataMode::Scanning);
			main_status_ &= ~(StatusCB | StatusNDM);
			command_.clear();

	// Sets the data request bit, and waits for a byte. Then sets the busy bit. Continues accepting bytes
	// until it has a quantity that make up an entire command, then resets the data request bit and
	// branches to that command.
	wait_for_complete_command_sequence:
			main_status_ |= StatusRQM;
			WAIT_FOR_EVENT(Event8272::CommandByte)
			main_status_ |= StatusCB;

			switch(command_[0] & 0x1f) {
				case 0x06:	// read data
					if(command_.size() < 9) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto read_data;

				case 0x0b:	// read deleted data
					if(command_.size() < 9) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto read_deleted_data;

				case 0x05:	// write data
					if(command_.size() < 9) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto write_data;

				case 0x09:	// write deleted data
					if(command_.size() < 9) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto write_deleted_data;

				case 0x02:	// read track
					if(command_.size() < 9) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto read_track;

				case 0x0a:	// read ID
					if(command_.size() < 2) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto read_id;

				case 0x0d:	// format track
					if(command_.size() < 6) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto format_track;

				case 0x11:	// scan low
					if(command_.size() < 9) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto scan_low;

				case 0x19:	// scan low or equal
					if(command_.size() < 9) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto scan_low_or_equal;

				case 0x1d:	// scan high or equal
					if(command_.size() < 9) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto scan_high_or_equal;

				case 0x07:	// recalibrate
					if(command_.size() < 2) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto recalibrate;

				case 0x08:	// sense interrupt status
					main_status_ &= ~StatusRQM;
					goto sense_interrupt_status;

				case 0x03:	// specify
					if(command_.size() < 3) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto specify;

				case 0x04:	// sense drive status
					if(command_.size() < 2) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto sense_drive_status;

				case 0x0f:	// seek
					if(command_.size() < 3) goto wait_for_complete_command_sequence;
					main_status_ &= ~StatusRQM;
					goto seek;

				default:	// invalid
					main_status_ &= ~StatusRQM;
					goto invalid;
			}

	// Performs the read data command.
	read_data:
			printf("Read data, sector %02x %02x %02x %02x\n", command_[2], command_[3], command_[4], command_[5]);

		// Establishes the drive and head being addressed, and whether in double density mode; populates the internal
		// cylinder, head, sector and size registers from the command stream.
			SET_DRIVE_HEAD_MFM();
			cylinder_ = command_[2];
			head_ = command_[3];
			sector_ = command_[4];
			size_ = command_[5];

		// Sets a maximum index hole limit of 2 then performs a find header/read header loop, continuing either until
		// the index hole limit is breached or a sector is found with a cylinder, head, sector and size equal to the
		// values in the internal registers.
			index_hole_limit_ = 2;
		find_next_sector:
			FIND_HEADER();
			if(!index_hole_limit_) goto read_data_not_found;
			READ_HEADER();
			if(header_[0] != cylinder_ || header_[1] != head_ || header_[2] != sector_ || header_[3] != size_) goto find_next_sector;

		// Finds the next data block and sets data mode to reading.
			FIND_DATA();
			distance_into_section_ = 0;
			set_data_mode(Reading);

		// Waits for the next token, then supplies it to the CPU by: (i) setting data request and direction; and (ii) resetting
		// data request once the byte has been taken. Continues until all bytes have been read.
		//
		// TODO: signal if the CPU is too slow and missed a byte; at the minute it'll just silently miss. Also allow for other
		// ways that sector size might have been specified.
		get_byte:
			WAIT_FOR_EVENT(Event::Token);
			result_stack_.push_back(get_latest_token().byte_value);
			distance_into_section_++;
			main_status_ |= StatusRQM | StatusDIO;
			WAIT_FOR_EVENT(Event8272::ResultEmpty);
			main_status_ &= ~StatusRQM;
			if(distance_into_section_ < (128 << size_)) goto get_byte;

		// For a final result phase, post the standard ST0, ST1, ST2, C, H, R, N
			goto post_st012chrn;

		// Execution reaches here if two index holes were discovered before a matching sector — i.e. the data wasn't found.
		// In that case set appropriate error flags and post the results.
		read_data_not_found:
			printf("Not found\n");

			status_[1] |= 0x4;
			status_[0] = 0x40;	// (status_[0] & ~0xc0) |
			goto post_st012chrn;

	read_deleted_data:
		printf("Read deleted data unimplemented!!\n");
		goto wait_for_command;

	write_data:
		printf("Write data unimplemented!!\n");
		goto wait_for_command;

	write_deleted_data:
		printf("Write deleted data unimplemented!!\n");
		goto wait_for_command;

	read_track:
		printf("Read track unimplemented!!\n");
		goto wait_for_command;

	// Performs the read ID command.
	read_id:
		// Establishes the drive and head being addressed, and whether in double density mode.
			printf("Read ID\n");
			SET_DRIVE_HEAD_MFM();

		// Sets a maximum index hole limit of 2 then waits either until it finds a header mark or sees too many index holes.
		// If a header mark is found, reads in the following bytes that produce a header. Otherwise branches to data not found.
			index_hole_limit_ = 2;
		read_id_find_next_sector:
			FIND_HEADER();
			if(!index_hole_limit_) goto read_data_not_found;
			READ_HEADER();

		// Sets internal registers from the discovered header and posts the standard ST0, ST1, ST2, C, H, R, N.
			cylinder_ = header_[0];
			head_ = header_[1];
			sector_ = header_[2];
			size_ = header_[3];

			goto post_st012chrn;

	format_track:
		printf("Fromat track unimplemented!!\n");
		goto wait_for_command;

	scan_low:
		printf("Scan low unimplemented!!\n");
		goto wait_for_command;

	scan_low_or_equal:
		printf("Scan low or equal unimplemented!!\n");
		goto wait_for_command;

	scan_high_or_equal:
		printf("Scan high or equal unimplemented!!\n");
		goto wait_for_command;

	// Performs both recalibrate and seek commands. These commands occur asynchronously, so the actual work
	// occurs in ::run_for; this merely establishes that seeking should be ongoing.
	recalibrate:
	seek:
			printf((command_.size() > 2) ? "Seek\n" : "Recalibrate\n");

		// Declines to act if a seek is already ongoing; otherwise resets all status registers, sets the drive
		// into seeking mode, sets the drive's main status seeking bit, and sets the target head position: for
		// a recalibrate the target is -1 and ::run_for knows that -1 means the terminal condition is the drive
		// returning that its at track zero, and that it should reset the drive's current position once reached.
			if(drives_[command_[1]&3].phase != Drive::Seeking) {
				status_[0] = status_[1] = status_[2] = 0;
				int drive = command_[1]&3;
				drives_[drive].phase = Drive::Seeking;
				drives_[drive].steps_taken = 0;
				drives_[drive].target_head_position = (command_.size() > 2) ? command_[2] : -1;
				drives_[drive].step_rate_counter = 0;

				// Check whether any steps are even needed.
				if(seek_is_satisfied(drive)) {
					drives_[drive].phase = Drive::CompletedSeeking;
				} else {
					main_status_ |= 1 << (command_[1]&3);
				}
			}
			goto wait_for_command;

	// Performs sense interrupt status.
	sense_interrupt_status:
			printf("Sense interrupt status\n");
			{
				// Find the first drive that is in the CompletedSeeking state.
				int found_drive = -1;
				for(int c = 0; c < 4; c++) {
					if(drives_[c].phase == Drive::CompletedSeeking) {
						found_drive = c;
						break;
					}
				}

				// If a drive was found, return its results. Otherwise return a single 0x80.
				if(found_drive != -1) {
					drives_[found_drive].phase = Drive::NotSeeking;
					status_[0] = (uint8_t)found_drive | 0x20;
					main_status_ &= ~(1 << found_drive);

					result_stack_.push_back(drives_[found_drive].head_position);
					result_stack_.push_back(status_[0]);
				} else {
					result_stack_.push_back(0x80);
				}
			}
			goto post_result;

	// Performs specify.
	specify:
		// Just store the values, and terminate the command.
			step_rate_time_ = command_[1] &0xf0;		// i.e. 16 to 240m
			head_unload_time_ = command_[1] & 0x0f;		// i.e. 1 to 16ms
			head_load_time_ = command_[2] & ~1;			// i.e. 2 to 254 ms in increments of 2ms
			dma_mode_ = !(command_[2] & 1);
			goto wait_for_command;

	sense_drive_status:
		printf("Sense drive status unimplemented!!\n");
		goto wait_for_command;

	// Performs any invalid command.
	invalid:
			// A no-op, but posts ST0.
			result_stack_.push_back(status_[0]);
			goto post_result;

	// Posts ST0, ST1, ST2, C, H, R and N as a result phase.
	post_st012chrn:
			result_stack_.push_back(size_);
			result_stack_.push_back(sector_);
			result_stack_.push_back(head_);
			result_stack_.push_back(cylinder_);

			result_stack_.push_back(status_[2]);
			result_stack_.push_back(status_[1]);
			result_stack_.push_back(status_[0]);

			goto post_result;

	// Posts whatever is in result_stack_ as a result phase. Be aware that it is a stack — the
	// last thing in it will be returned first.
	post_result:
			// Set ready to send data to the processor, no longer in non-DMA execution phase.
			main_status_ |= StatusRQM | StatusDIO;
			main_status_ &= ~StatusNDM;

			// The actual stuff of unwinding result_stack_ is handled by ::get_register; wait
			// until the processor has read all result bytes.
			WAIT_FOR_EVENT(Event8272::ResultEmpty);

			// Reset data direction and end the command.
			main_status_ &= ~StatusDIO;
			goto wait_for_command;

	END_SECTION()
}

bool i8272::seek_is_satisfied(int drive) {
	return	(drives_[drive].target_head_position == drives_[drive].head_position) ||
			(drives_[drive].target_head_position == -1 && drives_[drive].drive->get_is_track_zero());
}