/*
	990_hd.c: emulation of a generic ti990 hard disk controller, for use with
	TILINE-based TI990 systems (TI990/10, /12, /12LR, /10A, Business system 300
	and 300A).

	This core will emulate the common feature set found in every disk controller.
	Most controllers support additional features, but are still compatible with
	the basic feature set.  I have a little documentation on two specific
	disk controllers (WD900 and WD800/WD800A), but I have not tried to emulate
	controller-specific features.


	Long description: see 2234398-9701 and 2306140-9701.


	Raphael Nabet 2002-2003
*/

#include "driver.h"

#include "990_hd.h"
#include "image.h"

#include "harddisk.h"
#include "devices/harddriv.h"

static void update_interrupt(void);

/* max disk units per controller: 4 is the protocol limit, but it may be
overriden if more than one controller is used */
#define MAX_DISK_UNIT 4

/* Max sector lenght is bytes.  Generally 256, except for a few older disk
units which use 288-byte-long sectors, and SCSI units which generally use
standard 512-byte-long sectors. */
/* I chose a limit of 512.  No need to use more until someone writes CD-ROMs
for TI990. */
#define MAX_SECTOR_SIZE 512

/* Description of custom format */
/* We can use MAME's harddisk.c image format instead. */

/* machine-independant big-endian 32-bit integer */
typedef struct UINT32BE
{
	UINT8 bytes[4];
} UINT32BE;

INLINE UINT32 get_UINT32BE(UINT32BE word)
{
	return (word.bytes[0] << 24) | (word.bytes[1] << 16) | (word.bytes[2] << 8) | word.bytes[3];
}

/*INLINE void set_UINT32BE(UINT32BE *word, UINT32 data)
{
	word->bytes[0] = (data >> 24) & 0xff;
	word->bytes[1] = (data >> 16) & 0xff;
	word->bytes[2] = (data >> 8) & 0xff;
	word->bytes[3] = data & 0xff;
}*/

/* disk image header */
typedef struct disk_image_header
{
	UINT32BE cylinders;			/* number of cylinders on hard disk (big-endian) */
	UINT32BE heads;				/* number of heads on hard disk (big-endian) */
	UINT32BE sectors_per_track;	/* number of sectors per track on hard disk (big-endian) */
	UINT32BE bytes_per_sector;	/* number of bytes of data per sector on hard disk (big-endian) */
} disk_image_header;

enum
{
	header_len = sizeof(disk_image_header)
};

/* disk drive unit descriptor */
typedef struct hd_unit_t
{
	mess_image *img;						/* image descriptor */
	enum { format_mame, format_old } format;
	hard_disk_file *hd_handle;		/* mame hard disk descriptor - only if format == format_mame */
	unsigned int wp : 1;					/* TRUE if disk is write-protected */
	unsigned int unsafe : 1;				/* TRUE when a disk has just been connected */

	/* disk geometry */
	unsigned int cylinders, heads, sectors_per_track, bytes_per_sector;
} hd_unit_t;

/* disk controller */
typedef struct hdc_t
{
	UINT16 w[8];

	void (*interrupt_callback)(int state);

	hd_unit_t d[MAX_DISK_UNIT];
} hdc_t;

/* masks for individual bits controller registers */
enum
{
	w0_offline			= 0x8000,
	w0_not_ready		= 0x4000,
	w0_write_protect	= 0x2000,
	w0_unsafe			= 0x1000,
	w0_end_of_cylinder	= 0x0800,
	w0_seek_incomplete	= 0x0400,
	/*w0_offset_active	= 0x0200,*/
	w0_pack_change		= 0x0100,

	w0_attn_lines		= 0x00f0,
	w0_attn_mask		= 0x000f,

	w1_extended_command	= 0xc000,
	/*w1_strobe_early		= 0x2000,
	w1_strobe_late		= 0x1000,*/
	w1_transfer_inhibit	= 0x0800,
	w1_command			= 0x0700,
	w1_offset			= 0x0080,
	w1_offset_forward	= 0x0040,
	w1_head_address		= 0x003f,

	w6_unit0_sel		= 0x0800,
	w6_unit1_sel		= 0x0400,
	w6_unit2_sel		= 0x0200,
	w6_unit3_sel		= 0x0100,

	w7_idle				= 0x8000,
	w7_complete			= 0x4000,
	w7_error			= 0x2000,
	w7_int_enable		= 0x1000,
	/*w7_lock_out			= 0x0800,*/
	w7_retry			= 0x0400,
	w7_ecc				= 0x0200,
	w7_abnormal_completion	= 0x0100,
	w7_memory_error			= 0x0080,
	w7_data_error			= 0x0040,
	w7_tiline_timeout_err	= 0x0020,
	w7_header_err			= 0x0010,
	w7_rate_err				= 0x0008,
	w7_command_time_out_err	= 0x0004,
	w7_search_err			= 0x0002,
	w7_unit_err				= 0x0001
};

/* masks for computer-controlled bit in each controller register  */
static const UINT16 w_mask[8] =
{
	0x000f,		/* Controllers should prevent overwriting of w0 status bits, and I know
				that some controllers do so. */
	0xffff,
	0xffff,
	0xffff,
	0xffff,
	0xffff,
	0xffff,
	0xf7ff		/* Don't overwrite reserved bits */
};

static hdc_t hdc;


/*
	Initialize hard disk unit
*/
DEVICE_INIT( ti990_hd )
{
	hd_unit_t *d;
	int id = image_index_in_device(image);


	if ((id < 0) || (id >= MAX_DISK_UNIT))
		return INIT_FAIL;

	d = &hdc.d[id];
	memset(d, 0, sizeof(*d));

	d->img = image;
	d->format = format_mame;	/* don't care */
	d->hd_handle = NULL;
	d->wp = 1;
	d->unsafe = 1;

	/* clear attention line */
	/*hdc.w[0] &= ~ (0x80 >> id);*/

	return device_init_mess_hd(image);
}

/*DEVICE_EXIT( ti990_hd )
{
	d->img = NULL;
}*/

/*
	Initialize hard disk unit and open a hard disk image
*/
DEVICE_LOAD( ti990_hd )
{
	int id = image_index_in_device(image);
	hd_unit_t *d;
	char tag[8];
	const hard_disk_info *standard_header;
	disk_image_header custom_header;
	int bytes_read;


	if ((id < 0) || (id >= MAX_DISK_UNIT))
		return INIT_FAIL;

	d = &hdc.d[id];

	bytes_read = image_fread(image, tag, sizeof(tag));
	if (bytes_read != sizeof(tag))
		return INIT_FAIL;;
	if (! strncmp(tag, "MComprHD", 8))
	{
		/* standard hard disk format */

		/* open image */
		if (device_load_mess_hd(image))
			return INIT_FAIL;

		/* set file descriptor */
		d->format = format_mame;
		d->hd_handle = mess_hd_get_hard_disk_file(image);
		/* tell whether the image is writable */
		d->wp = !image_is_writable(image);
	}
	else
	{
		/* older, custom format */

		/* set file descriptor */
		d->format = format_old;
		d->hd_handle = NULL;
		/* tell whether the image is writable */
		d->wp = ! image_is_writable(image);
	}

	d->unsafe = 1;
	/* set attention line */
	hdc.w[0] |= (0x80 >> id);

	/* read geometry */
	switch (d->format)
	{
	case format_mame:
		/* use standard hard disk image header. */
		standard_header = hard_disk_get_info(d->hd_handle);

		d->cylinders = standard_header->cylinders;
		d->heads = standard_header->heads;
		d->sectors_per_track = standard_header->sectors;
		d->bytes_per_sector = standard_header->sectorbytes;
		break;

	case format_old:
		/* use custom image header. */
		/* to convert old header-less images to this format, insert a 16-byte
		header as follow: 00 00 03 8f  00 00 00 05  00 00 00 21  00 00 01 00 */
		image_fseek(d->img, 0, SEEK_SET);
		bytes_read = image_fread(d->img, &custom_header, sizeof(custom_header));
		if (bytes_read != sizeof(custom_header))
		{
			device_unload_ti990_hd(image);
			return INIT_FAIL;
		}

		d->cylinders = get_UINT32BE(custom_header.cylinders);
		d->heads = get_UINT32BE(custom_header.heads);
		d->sectors_per_track = get_UINT32BE(custom_header.sectors_per_track);
		d->bytes_per_sector = get_UINT32BE(custom_header.bytes_per_sector);
		break;
	}

	if (d->bytes_per_sector > MAX_SECTOR_SIZE)
	{
		device_unload_ti990_hd(image);
		return INIT_FAIL;
	}

	return INIT_PASS;
}

/*
	close a hard disk image
*/
DEVICE_UNLOAD( ti990_hd )
{
	int id = image_index_in_device(image);
	hd_unit_t *d;

	if ((id < 0) || (id >= MAX_DISK_UNIT))
		return;

	d = &hdc.d[id];

	switch (d->format)
	{
	case format_mame:
		device_unload_mess_hd(image);
		break;

	case format_old:
		/* no additional clean up is needed */
		break;
	}

	d->format = format_mame;	/* don't care */
	d->hd_handle = NULL;
	d->wp = 1;
	d->unsafe = 1;

	/* clear attention line */
	hdc.w[0] &= ~ (0x80 >> id);
}

/*
	Return true if a HD image has been loaded
*/
INLINE int is_unit_loaded(int unit)
{
	int reply = 0;

	switch (hdc.d[unit].format)
	{
	case format_mame:
		reply = (hdc.d[unit].hd_handle != NULL);
		break;

	case format_old:
		reply = (image_exists(hdc.d[unit].img) ? 1 : 0);
		break;
	}

	return reply;
}

/*
	Init the hdc core
*/
void ti990_hdc_init(void (*interrupt_callback)(int state))
{
	int i;


	memset(hdc.w, 0, sizeof(hdc.w));
	hdc.w[7] = w7_idle;
	/* set attention lines */
	for (i=0; i<MAX_DISK_UNIT; i++)
		if (is_unit_loaded(i))
			hdc.w[0] |= (0x80 >> i);

	hdc.interrupt_callback = interrupt_callback;

	update_interrupt();
}

/*
	Parse the disk select lines, and return the corresponding tape unit.
	(-1 if none)
*/
static int cur_disk_unit(void)
{
	int reply;


	if (hdc.w[6] & w6_unit0_sel)
		reply = 0;
	else if (hdc.w[6] & w6_unit1_sel)
		reply = 1;
	else if (hdc.w[6] & w6_unit2_sel)
		reply = 2;
	else if (hdc.w[6] & w6_unit3_sel)
		reply = 3;
	else
		reply = -1;

	if (reply >= MAX_DISK_UNIT)
		reply = -1;

	return reply;
}

/*
	Update interrupt state
*/
static void update_interrupt(void)
{
	if (hdc.interrupt_callback)
		(*hdc.interrupt_callback)((hdc.w[7] & w7_idle)
									&& (((hdc.w[7] & w7_int_enable) && (hdc.w[7] & (w7_complete | w7_error)))
										|| ((hdc.w[0] & (hdc.w[0] >> 4)) & w0_attn_mask)));
}

/*
	Check that a sector address is valid.

	Terminate current command and return non-zero if the address is invalid.
*/
static int check_sector_address(int unit, unsigned int cylinder, unsigned int head, unsigned int sector)
{
	if ((cylinder > hdc.d[unit].cylinders) || (head > hdc.d[unit].heads) || (sector > hdc.d[unit].sectors_per_track))
	{	/* invalid address */
		if (cylinder > hdc.d[unit].cylinders)
		{
			hdc.w[0] |= w0_seek_incomplete;
			hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		}
		else if (head > hdc.d[unit].heads)
		{
			hdc.w[0] |= w0_end_of_cylinder;
			hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		}
		else if (sector > hdc.d[unit].sectors_per_track)
			hdc.w[7] |= w7_idle | w7_error | w7_command_time_out_err;
		update_interrupt();
		return 1;
	}

	return 0;
}

/*
	Seek to sector whose address is given
*/
static int sector_to_lba(int unit, unsigned int cylinder, unsigned int head, unsigned int sector, unsigned int *lba)
{
	if (check_sector_address(unit, cylinder, head, sector))
		return 1;

	* lba = (cylinder*hdc.d[unit].heads + head)*hdc.d[unit].sectors_per_track + sector;

	return 0;
}

/*
	Read one given sector
*/
static int read_sector(int unit, unsigned int lba, void *buffer, unsigned int bytes_to_read)
{
	unsigned long byte_position;
	unsigned int bytes_read;

	switch (hdc.d[unit].format)
	{
	case format_mame:
		bytes_read = hdc.d[unit].bytes_per_sector * hard_disk_read(hdc.d[unit].hd_handle, lba, buffer);
		if (bytes_read > bytes_to_read)
			bytes_read = bytes_to_read;
		break;

	case format_old:
		byte_position = lba*hdc.d[unit].bytes_per_sector + header_len;
		image_fseek(hdc.d[unit].img, byte_position, SEEK_SET);
		bytes_read = image_fread(hdc.d[unit].img, buffer, bytes_to_read);
		break;

	default:
		bytes_read = 0;
		break;
	}

	return bytes_read;
}

/*
	Write one given sector
*/
static int write_sector(int unit, unsigned int lba, const void *buffer, unsigned int bytes_to_write)
{
	unsigned long byte_position;
	unsigned int bytes_written;

	switch (hdc.d[unit].format)
	{
	case format_mame:
		bytes_written = hdc.d[unit].bytes_per_sector * hard_disk_write(hdc.d[unit].hd_handle, lba, buffer);
		if (bytes_written > bytes_to_write)
			bytes_written = bytes_to_write;
		break;

	case format_old:
		byte_position = lba*hdc.d[unit].bytes_per_sector + header_len;
		image_fseek(hdc.d[unit].img, byte_position, SEEK_SET);
		bytes_written = image_fwrite(hdc.d[unit].img, buffer, bytes_to_write);
		break;

	default:
		bytes_written = 0;
		break;
	}

	return bytes_written;
}

/*
	Handle the store registers command: read the drive geometry.
*/
static void store_registers(void)
{
	int dma_address;
	int byte_count;

	UINT16 buffer[3];
	int i, real_word_count;

	int dsk_sel = cur_disk_unit();


	if (dsk_sel == -1)
	{
		/* No idea what to report... */
		hdc.w[7] |= w7_idle | w7_error | w7_abnormal_completion;
		update_interrupt();
		return;
	}
	else if (! is_unit_loaded(dsk_sel))
	{	/* offline */
		hdc.w[0] |= w0_offline | w0_not_ready;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}

	hdc.d[dsk_sel].unsafe = 0;		/* I think */

	dma_address = ((((int) hdc.w[6]) << 16) | hdc.w[5]) & 0x1ffffe;
	byte_count = hdc.w[4] & 0xfffe;

	/* formatted words per track */
	buffer[0] = (hdc.d[dsk_sel].sectors_per_track*hdc.d[dsk_sel].bytes_per_sector) >> 1;
	/* MSByte: sectors per track; LSByte: bytes of overhead per sector */
	buffer[1] = (hdc.d[dsk_sel].sectors_per_track << 8) | 0;
	/* bits 0-4: heads; bits 5-15: cylinders */
	buffer[2] = (hdc.d[dsk_sel].heads << 11) | hdc.d[dsk_sel].cylinders;

	real_word_count = byte_count >> 1;
	if (real_word_count > 3)
		real_word_count = 3;

	/* DMA */
	if (! (hdc.w[1] & w1_transfer_inhibit))
		for (i=0; i<real_word_count; i++)
		{
			program_write_word_16be(dma_address, buffer[i]);
			dma_address = (dma_address + 2) & 0x1ffffe;
		}

	hdc.w[7] |= w7_idle | w7_complete;
	update_interrupt();
}

/*
	Handle the write format command: format a complete track on disk.

	The emulation just clears the track data in the disk image.
*/
static void write_format(void)
{
	unsigned int cylinder, head, sector;
	unsigned int lba;

	UINT8 buffer[MAX_SECTOR_SIZE];
	int bytes_written;

	int dsk_sel = cur_disk_unit();


	if (dsk_sel == -1)
	{
		/* No idea what to report... */
		hdc.w[7] |= w7_idle | w7_error | w7_abnormal_completion;
		update_interrupt();
		return;
	}
	else if (! is_unit_loaded(dsk_sel))
	{	/* offline */
		hdc.w[0] |= w0_offline | w0_not_ready;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}
	else if (hdc.d[dsk_sel].unsafe)
	{	/* disk in unsafe condition */
		hdc.w[0] |= w0_unsafe | w0_pack_change;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}
	else if (hdc.d[dsk_sel].wp)
	{	/* disk write-protected */
		hdc.w[0] |= w0_write_protect;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}

	cylinder = hdc.w[3];
	head = hdc.w[1] & w1_head_address;

	if (sector_to_lba(dsk_sel, cylinder, head, 0, &lba))
		return;

	memset(buffer, 0, hdc.d[dsk_sel].bytes_per_sector);

	for (sector=0; sector<hdc.d[dsk_sel].sectors_per_track; sector++)
	{
		bytes_written = write_sector(dsk_sel, lba, buffer, hdc.d[dsk_sel].bytes_per_sector);

		if (bytes_written != hdc.d[dsk_sel].bytes_per_sector)
		{
			hdc.w[0] |= w0_offline | w0_not_ready;
			hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
			update_interrupt();
			return;
		}

		lba++;
	}

	hdc.w[7] |= w7_idle | w7_complete;
	update_interrupt();
}

/*
	Handle the read data command: read a variable number of sectors from disk.
*/
static void read_data(void)
{
	int dma_address;
	int byte_count;

	unsigned int cylinder, head, sector;
	unsigned int lba;

	UINT8 buffer[MAX_SECTOR_SIZE];
	int bytes_to_read;
	int bytes_read;
	int i;

	int dsk_sel = cur_disk_unit();


	if (dsk_sel == -1)
	{
		/* No idea what to report... */
		hdc.w[7] |= w7_idle | w7_error | w7_abnormal_completion;
		update_interrupt();
		return;
	}
	else if (! is_unit_loaded(dsk_sel))
	{	/* offline */
		hdc.w[0] |= w0_offline | w0_not_ready;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}
	else if (hdc.d[dsk_sel].unsafe)
	{	/* disk in unsafe condition */
		hdc.w[0] |= w0_unsafe | w0_pack_change;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}

	dma_address = ((((int) hdc.w[6]) << 16) | hdc.w[5]) & 0x1ffffe;
	byte_count = hdc.w[4] & 0xfffe;

	cylinder = hdc.w[3];
	head = hdc.w[1] & w1_head_address;
	sector = hdc.w[2] & 0xff;

	if (sector_to_lba(dsk_sel, cylinder, head, sector, &lba))
		return;

	while (byte_count)
	{	/* read data sector per sector */
		if (cylinder > hdc.d[dsk_sel].cylinders)
		{
			hdc.w[0] |= w0_seek_incomplete;
			hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
			update_interrupt();
			return;
		}

		bytes_to_read = (byte_count < hdc.d[dsk_sel].bytes_per_sector) ? byte_count : hdc.d[dsk_sel].bytes_per_sector;
		bytes_read = read_sector(dsk_sel, lba, buffer, bytes_to_read);

		if (bytes_read != bytes_to_read)
		{	/* behave as if the controller could not found the sector ID mark */
			hdc.w[7] |= w7_idle | w7_error | w7_command_time_out_err;
			update_interrupt();
			return;
		}

		/* DMA */
		if (! (hdc.w[1] & w1_transfer_inhibit))
			for (i=0; i<bytes_read; i+=2)
			{
				program_write_word_16be(dma_address, (((int) buffer[i]) << 8) | buffer[i+1]);
				dma_address = (dma_address + 2) & 0x1ffffe;
			}

		byte_count -= bytes_read;

		/* update sector address to point to next sector */
		lba++;
		sector++;
		if (sector == hdc.d[dsk_sel].sectors_per_track)
		{
			sector = 0;
			head++;
			if (head == hdc.d[dsk_sel].heads)
			{
				head = 0;
				cylinder++;
			}
		}
	}

	hdc.w[7] |= w7_idle | w7_complete;
	update_interrupt();
}

/*
	Handle the write data command: write a variable number of sectors from disk.
*/
static void write_data(void)
{
	int dma_address;
	int byte_count;

	unsigned int cylinder, head, sector;
	unsigned int lba;

	UINT8 buffer[MAX_SECTOR_SIZE];
	UINT16 word;
	int bytes_written;
	int i;

	int dsk_sel = cur_disk_unit();


	if (dsk_sel == -1)
	{
		/* No idea what to report... */
		hdc.w[7] |= w7_idle | w7_error | w7_abnormal_completion;
		update_interrupt();
		return;
	}
	else if (! is_unit_loaded(dsk_sel))
	{	/* offline */
		hdc.w[0] |= w0_offline | w0_not_ready;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}
	else if (hdc.d[dsk_sel].unsafe)
	{	/* disk in unsafe condition */
		hdc.w[0] |= w0_unsafe | w0_pack_change;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}
	else if (hdc.d[dsk_sel].wp)
	{	/* disk write-protected */
		hdc.w[0] |= w0_write_protect;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}

	dma_address = ((((int) hdc.w[6]) << 16) | hdc.w[5]) & 0x1ffffe;
	byte_count = hdc.w[4] & 0xfffe;

	cylinder = hdc.w[3];
	head = hdc.w[1] & w1_head_address;
	sector = hdc.w[2] & 0xff;

	if (sector_to_lba(dsk_sel, cylinder, head, sector, &lba))
		return;

	while (byte_count > 0)
	{	/* write data sector per sector */
		if (cylinder > hdc.d[dsk_sel].cylinders)
		{
			hdc.w[0] |= w0_seek_incomplete;
			hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
			update_interrupt();
			return;
		}

		/* DMA */
		for (i=0; (i<byte_count) && (i<hdc.d[dsk_sel].bytes_per_sector); i+=2)
		{
			word = program_read_word_16be(dma_address);
			buffer[i] = word >> 8;
			buffer[i+1] = word & 0xff;

			dma_address = (dma_address + 2) & 0x1ffffe;
		}
		/* fill with 0s if we did not reach sector end */
		for (; i<hdc.d[dsk_sel].bytes_per_sector; i+=2)
			buffer[i] = buffer[i+1] = 0;

		bytes_written = write_sector(dsk_sel, lba, buffer, hdc.d[dsk_sel].bytes_per_sector);

		if (bytes_written != hdc.d[dsk_sel].bytes_per_sector)
		{
			hdc.w[0] |= w0_offline | w0_not_ready;
			hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
			update_interrupt();
			return;
		}

		byte_count -= bytes_written;

		/* update sector address to point to next sector */
		lba++;
		sector++;
		if (sector == hdc.d[dsk_sel].sectors_per_track)
		{
			sector = 0;
			head++;
			if (head == hdc.d[dsk_sel].heads)
			{
				head = 0;
				cylinder++;
			}
		}
	}

	hdc.w[7] |= w7_idle | w7_complete;
	update_interrupt();
}

/*
	Handle the unformatted read command: read drive geometry information.
*/
static void unformatted_read(void)
{
	int dma_address;
	int byte_count;

	unsigned int cylinder, head, sector;

	UINT16 buffer[3];
	int i, real_word_count;

	int dsk_sel = cur_disk_unit();


	if (dsk_sel == -1)
	{
		/* No idea what to report... */
		hdc.w[7] |= w7_idle | w7_error | w7_abnormal_completion;
		update_interrupt();
		return;
	}
	else if (! is_unit_loaded(dsk_sel))
	{	/* offline */
		hdc.w[0] |= w0_offline | w0_not_ready;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}
	else if (hdc.d[dsk_sel].unsafe)
	{	/* disk in unsafe condition */
		hdc.w[0] |= w0_unsafe | w0_pack_change;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}

	dma_address = ((((int) hdc.w[6]) << 16) | hdc.w[5]) & 0x1ffffe;
	byte_count = hdc.w[4] & 0xfffe;

	cylinder = hdc.w[3];
	head = hdc.w[1] & w1_head_address;
	sector = hdc.w[2] & 0xff;

	if (check_sector_address(dsk_sel, cylinder, head, sector))
		return;

	dma_address = ((((int) hdc.w[6]) << 16) | hdc.w[5]) & 0x1ffffe;
	byte_count = hdc.w[4] & 0xfffe;

	/* bits 0-4: head address; bits 5-15: cylinder address */
	buffer[0] = (head << 11) | cylinder;
	/* MSByte: sectors per record (1); LSByte: sector address */
	buffer[1] = (1 << 8) | sector;
	/* formatted words per record */
	buffer[2] = hdc.d[dsk_sel].bytes_per_sector >> 1;

	real_word_count = byte_count >> 1;
	if (real_word_count > 3)
		real_word_count = 3;

	/* DMA */
	if (! (hdc.w[1] & w1_transfer_inhibit))
		for (i=0; i<real_word_count; i++)
		{
			program_write_word_16be(dma_address, buffer[i]);
			dma_address = (dma_address + 2) & 0x1ffffe;
		}

	hdc.w[7] |= w7_idle | w7_complete;
	update_interrupt();
}

/*
	Handle the restore command: return to track 0.
*/
static void restore(void)
{
	int dsk_sel = cur_disk_unit();


	if (dsk_sel == -1)
	{
		/* No idea what to report... */
		hdc.w[7] |= w7_idle | w7_error | w7_abnormal_completion;
		update_interrupt();
		return;
	}
	else if (! is_unit_loaded(dsk_sel))
	{	/* offline */
		hdc.w[0] |= w0_offline | w0_not_ready;
		hdc.w[7] |= w7_idle | w7_error | w7_unit_err;
		update_interrupt();
		return;
	}

	hdc.d[dsk_sel].unsafe = 0;		/* I think */

	/*if (seek_to_sector(dsk_sel, 0, 0, 0))
		return;*/

	hdc.w[7] |= w7_idle | w7_complete;
	update_interrupt();
}

/*
	Parse command code and execute the command.
*/
static void execute_command(void)
{
	/* hack */
	hdc.w[0] &= 0xff;

	if (hdc.w[1] & w1_extended_command)
		logerror("extended commands not supported\n");

	switch (/*((hdc.w[1] & w1_extended_command) >> 11) |*/ ((hdc.w[1] & w1_command) >> 8))
	{
	case 0x00: //0b000:
		/* store registers */
		logerror("store registers\n");
		store_registers();
		break;
	case 0x01: //0b001:
		/* write format */
		logerror("write format\n");
		write_format();
		break;
	case 0x02: //0b010:
		/* read data */
		logerror("read data\n");
		read_data();
		break;
	case 0x03: //0b011:
		/* write data */
		logerror("write data\n");
		write_data();
		break;
	case 0x04: //0b100:
		/* unformatted read */
		logerror("unformatted read\n");
		unformatted_read();
		break;
	case 0x05: //0b101:
		/* unformatted write */
		logerror("unformatted write\n");
		/* ... */
		hdc.w[7] |= w7_idle | w7_error | w7_abnormal_completion;
		update_interrupt();
		break;
	case 0x06: //0b110:
		/* seek */
		logerror("seek\n");
		/* This command can (almost) safely be ignored */
		hdc.w[7] |= w7_idle | w7_complete;
		update_interrupt();
		break;
	case 0x07: //0b111:
		/* restore */
		logerror("restore\n");
		restore();
		break;
	}
}

/*
	Read one register in TPCS space
*/
READ16_HANDLER(ti990_hdc_r)
{
	if ((offset >= 0) && (offset < 8))
		return hdc.w[offset];
	else
		return 0;
}

/*
	Write one register in TPCS space.  Execute command if w7_idle is cleared.
*/
WRITE16_HANDLER(ti990_hdc_w)
{
	if ((offset >= 0) && (offset < 8))
	{
		/* write protect if a command is in progress */
		if (hdc.w[7] & w7_idle)
		{
			UINT16 old_data = hdc.w[offset];

			/* Only write writable bits AND honor byte accesses (ha!) */
			hdc.w[offset] = (hdc.w[offset] & ((~w_mask[offset]) | mem_mask)) | (data & w_mask[offset] & ~mem_mask);

			if ((offset == 0) || (offset == 7))
				update_interrupt();

			if ((offset == 7) && (old_data & w7_idle) && ! (data & w7_idle))
			{	/* idle has been cleared: start command execution */
				execute_command();
			}
		}
	}
}