// license:BSD-3-Clause
// copyright-holders:smf, Angelo Salese
/***************************************************************************

 gdrom.c - Implementation of the Sega GD-ROM device

***************************************************************************/

#include "emu.h"
#include "gdrom.h"

#define GDROM_BUSY_STATE    0x00
#define GDROM_PAUSE_STATE   0x01
#define GDROM_STANDBY_STATE 0x02
#define GDROM_PLAY_STATE    0x03
#define GDROM_SEEK_STATE    0x04
#define GDROM_SCAN_STATE    0x05
#define GDROM_OPEN_STATE    0x06
#define GDROM_NODISC_STATE  0x07
#define GDROM_RETRY_STATE   0x08
#define GDROM_ERROR_STATE   0x09


/*
 Officially not documented security-related packet commands:

 SYS_CHK_SECU (70h) Media security check
    Parameters: 1byte - R0011111, R - "recheck" (it seems actual security check performed automatically at drive power on or when disc was inserted, so normally this and next command returns result of already performed check.
                                      however, when MSB R bit is 1 will be forced media security recheck)
    Result: none
 SYS_REQ_SECU (71h) Request security data
    Parameters: 1byte - always 0x1f
    Result: a bit less than 1Kbyte chunk of data (length vary each time), contains real command reply obfuscated, which is extracted by such code:

   u8 reply[], real_reply[];
   for (u32 i = 0, offset = 0; i < length; i++)
   {
     offset++;
     u32 skip = reply[offset] - 2; // normally skip value is < 0x10, might be used to identify real reply length
     offset += skip;
     real_reply[i] = reply[offset++];
   }

   Real reply is 43 byte:
    struct sec_reply {
        u8 check_result;       // 0x1f - valid GD-ROM, 0x10 - valid Mil-CD (in this case following char[] fields is empty, 0x00-filled)
        char key_id[10];       // presumable Disc ID (T-xxxxxx or HDR-xxxxx etc)
        char key_maker_id[16]; // presumable "SEGA ENTERPRISES"
        char hard_id[16];      // presumable "SEGA SEGAKATANA "
    };

    *_id fields names came from Dev.box "Checker BIOS" disassembly, contents meaning is guesswork because all the reply dumps we have now was dumped with Mil-CD disc inserted but not GD-ROM.
    Presumable these data somehow encoded in GD-ROM disc HD area Lead-in (or Security Ring area ?), and compared with data in LD area IP.BIN by GD-drive firmware,
    as described in Sega patent EP0935242A1 https://patents.google.com/patent/EP0935242A1

    Dreamcast BIOS code verify only 1st result byte, if it's 5th bit (0x10) == 1.
    Naomi DIMM firmware verify if result byte equal to 0x1f.

 SYS_CHG_COMD (72h) ??? Authentication for next command ?
    Parameters: 1byte, probably key/password, in retail Dreamcast - 5th byte of unit SN# (located in flash ROM at 1A05Ah), 0 in Dev.box checker BIOS.
    Result: none

 SYS_REQ_COMD (73h) Request command list
    Parameters: none
    Result: chunk of data where obfuscated real reply, see command 71.
            real result: 14 bytes - codes of all regular (not security) packet commands supported by drive (00 10 11 12 13 14 15 16 20 21 22 30 31 40).

  Dreamcast BIOS SysCalls contain commands 0x72/73 routine, but it seems not used at practice.
*/

static const uint8_t GDROM_Cmd71_Reply[] =
{
	0x96, 0x0B, 0x45, 0xF0, 0x7E, 0xFF, 0x3D, 0x06, 0x4D, 0x7D, 0x10, 0xBF, 0x07, 0x00, 0x73, 0xCF,
	0x9C, 0x00, 0xBC, 0x0C, 0x1C, 0xAF, 0x1C, 0x30, 0xE7, 0xA7, 0x03, 0xA8, 0x98, 0x00, 0xBD, 0x0F,
	0xBD, 0x5B, 0xAA, 0x50, 0x23, 0x39, 0x31, 0x10, 0x0E, 0x69, 0x13, 0xE5, 0x00, 0xD2, 0x0D, 0x66,
	0x54, 0xBF, 0x5F, 0xFD, 0x37, 0x74, 0xF4, 0x5B, 0x22, 0x00, 0xC6, 0x09, 0x0F, 0xCA, 0x93, 0xE8,
	0xA4, 0xAB, 0x00, 0x61, 0x0E, 0x2E, 0xE1, 0x4B, 0x76, 0x8B, 0x6A, 0xA5, 0x9C, 0xE6, 0x23, 0xC4,
	0x00, 0x4B, 0x06, 0x1B, 0x91, 0x01, 0x00, 0xE2, 0x0D, 0xCF, 0xCA, 0x38, 0x3A, 0xB9, 0xE7, 0x91,
	0xE5, 0xEF, 0x4B, 0x00, 0xD6, 0x09, 0xD3, 0x68, 0x3E, 0xC4, 0xAF, 0x2D, 0x00, 0x2A, 0x0D, 0xF9,
	0xFC, 0x78, 0xED, 0xAE, 0x99, 0xB3, 0x32, 0x5A, 0xE7, 0x00, 0x4C, 0x0A, 0x22, 0x97, 0x5B, 0x82,
	0x06, 0x7A, 0x4C, 0x00, 0x42, 0x0E, 0x57, 0x78, 0x46, 0xF5, 0x20, 0xFC, 0x6B, 0xCB, 0x01, 0x5B,
	0x86, 0x00, 0xE4, 0x0E, 0xB2, 0x26, 0xCD, 0x71, 0xE3, 0xA5, 0x33, 0x06, 0x8E, 0x9A, 0x50, 0x00,
	0x07, 0x07, 0xF5, 0x34, 0xEF, 0xE6, 0x00, 0x32, 0x0F, 0x13, 0x41, 0x59, 0x56, 0x0F, 0x02, 0x38,
	0x2A, 0x64, 0x2A, 0x07, 0x3E, 0x00, 0x52, 0x11, 0x2A, 0x1D, 0x5F, 0x76, 0x66, 0xA0, 0xB2, 0x2F,
	0x97, 0xC7, 0x5E, 0x6E, 0x52, 0xE2, 0x00, 0x58, 0x09, 0xCA, 0x89, 0xA5, 0xDF, 0x0A, 0xDE, 0x00,
	0x50, 0x06, 0x49, 0xB8, 0xB4, 0x00, 0x77, 0x05, 0x24, 0xE8, 0x00, 0xBB, 0x0C, 0x91, 0x89, 0xA2,
	0x8B, 0x62, 0xDE, 0x6A, 0xC6, 0x60, 0x00, 0xE7, 0x0F, 0x0F, 0x11, 0x96, 0x55, 0xD2, 0xBF, 0xE6,
	0x48, 0x0B, 0x5C, 0xAB, 0xDC, 0x00, 0xBA, 0x0A, 0x30, 0xD7, 0x48, 0x0E, 0x78, 0x63, 0x0C, 0x00,
	0xD2, 0x0D, 0xFB, 0x8A, 0xA3, 0xFE, 0xF8, 0x3A, 0xDD, 0x88, 0xA9, 0x4B, 0x00, 0xA2, 0x0A, 0x75,
	0x5D, 0x0D, 0x37, 0x24, 0xC5, 0x9D, 0x00, 0xF7, 0x0B, 0x25, 0xEF, 0xDB, 0x41, 0xE0, 0x52, 0x3E,
	0x4E, 0x00, 0xB7, 0x03, 0x00, 0xE5, 0x11, 0xB9, 0xDE, 0x5A, 0x57, 0xCF, 0xB9, 0x1A, 0xFC, 0x7F,
	0x26, 0xEE, 0x7B, 0xCD, 0x2B, 0x00, 0x4B, 0x08, 0xB8, 0x09, 0x70, 0x6A, 0x9F, 0x00, 0x4B, 0x11,
	0x8C, 0x15, 0x87, 0xA3, 0x05, 0x4F, 0x37, 0x8E, 0x63, 0xDE, 0xEF, 0x39, 0xFC, 0x4B, 0x00, 0xAB,
	0x10, 0x0B, 0x91, 0xAA, 0x0F, 0xE1, 0xE9, 0xAE, 0x69, 0x3A, 0xF8, 0x03, 0x69, 0xD2, 0x00, 0xE2,
	0x07, 0xC1, 0x5C, 0x3D, 0x82, 0x00, 0xA9, 0x08, 0x68, 0xC4, 0xAD, 0x2E, 0xD1, 0x00, 0xF7, 0x0E,
	0xC6, 0x47, 0xC8, 0xCD, 0x8E, 0x7C, 0x00, 0x5C, 0x95, 0xB9, 0xF4, 0x00, 0xE3, 0x04, 0x5B, 0x00,
	0x74, 0x07, 0x65, 0xC7, 0x84, 0x8E, 0x00, 0xC6, 0x07, 0x61, 0x80, 0x44, 0x3F, 0x00, 0xC8, 0x0E,
	0x72, 0x78, 0x47, 0xD3, 0xC2, 0x4D, 0xAF, 0xC0, 0x54, 0x13, 0x31, 0x00, 0xF7, 0x0D, 0x48, 0xD8,
	0xE2, 0x92, 0x9F, 0x7F, 0x2F, 0x44, 0x68, 0x33, 0x00, 0x0D, 0x10, 0xAB, 0xFE, 0xEA, 0x8E, 0x19,
	0x81, 0xF8, 0x6F, 0x7C, 0xDE, 0xE1, 0xB3, 0x06, 0x00, 0x4D, 0x11, 0x66, 0xAE, 0x4C, 0xF9, 0xB7,
	0x2F, 0xEE, 0xB0, 0x8E, 0x7E, 0xE1, 0x8D, 0x95, 0x6F, 0x00, 0xF4, 0x0D, 0x88, 0x9D, 0xCA, 0xE3,
	0xC4, 0xB2, 0x47, 0xBB, 0xA0, 0x69, 0x00, 0xF3, 0x0B, 0x48, 0x17, 0x41, 0x64, 0xA0, 0x0E, 0x71,
	0x82, 0x00, 0x34, 0x1E, 0x18, 0x4D, 0x85, 0x80, 0x4C, 0xA9, 0x0B, 0x66, 0x9B, 0x75, 0x13, 0x61,
	0x70, 0x27, 0x81, 0x7A, 0x02, 0xCD, 0x57, 0xAB, 0xDF, 0x02, 0x93, 0x52, 0x83, 0xDF, 0x48, 0xA8,
	0xA6, 0x9E, 0x74, 0x6F, 0x89, 0x03, 0x28, 0x25, 0x52, 0x96, 0xFF, 0x67, 0x7A, 0xD8, 0x3C, 0xB1,
	0x2C, 0x46, 0x84, 0xEF, 0xE1, 0xC1, 0xC6, 0xC9, 0xDC, 0x96, 0xAA, 0xA9, 0xC4, 0x82, 0x58, 0x27,
	0x57, 0x75, 0x67, 0x34, 0xFB, 0x3B, 0x25, 0xBF, 0xFB, 0x3B, 0xF6, 0x13, 0xEC, 0x96, 0xE5, 0x16,
	0x26, 0xFD, 0xA8, 0xDA, 0x1B, 0xC6, 0x50, 0x7F, 0x47, 0xFF, 0x08, 0x55, 0x08, 0xED, 0x00, 0x93,
	0x9B, 0xC4, 0x71, 0x67, 0xEC, 0xA6, 0xCC, 0x16, 0x20, 0x87, 0x47, 0x07, 0xA6, 0x00, 0x79, 0x5D,
	0x4F, 0xAB, 0xA1, 0x6F, 0x7A, 0x6B, 0x27, 0xC4, 0xDA, 0xA3, 0xC3, 0x94, 0x4F, 0x7F, 0xF3, 0xE5,
	0x1B, 0x6F, 0xCC, 0xE5, 0xF0, 0xE5, 0x9D, 0xC9, 0xAE, 0xFD, 0x39, 0xAC, 0x4C, 0xE5, 0x58, 0x83,
	0x25, 0x65, 0x92, 0x74, 0x9E, 0x81, 0xA0, 0xB6, 0xA9, 0x02, 0x9B, 0x07, 0xB6, 0xE7, 0x79, 0x57,
	0xD9, 0x4A, 0xCE, 0xFA, 0xB4, 0x94, 0x05, 0xCC, 0x86, 0x3C, 0xDD, 0x06, 0xCD, 0xA6, 0x24, 0x24,
	0xFA, 0xC1, 0xF9, 0x48, 0xC9, 0x0C, 0x6C, 0xC4, 0x96, 0x82, 0x17, 0xF6, 0x31, 0x09, 0xC4, 0xE2,
	0x77, 0xFD, 0xCF, 0x46, 0x18, 0xB2, 0x5F, 0x01, 0x6B, 0xD1, 0x7B, 0x56, 0xB8, 0x94, 0x4A, 0xE5,
	0x6C, 0x19, 0xF0, 0xC0, 0xB6, 0x70, 0x93, 0xF7, 0xD3, 0xD1, 0x2B, 0x6E, 0x7C, 0x53, 0x6D, 0x85,
	0xD1, 0x0C, 0x8B, 0x77, 0xEE, 0x90, 0xDA, 0x15, 0x55, 0xE0, 0x58, 0x09, 0x56, 0xFC, 0x31, 0x9F,
	0xAF, 0x46, 0xCB, 0xC3, 0x8D, 0x71, 0x75, 0xF2, 0x2C, 0xC3, 0xBB, 0xA1, 0xC4, 0xCF, 0x27, 0x56,
	0x7C, 0x9B, 0xFE, 0xAF, 0x3E, 0x4E, 0xB4, 0xCD, 0x6A, 0xAA, 0xF5, 0xF3, 0xE3, 0x22, 0x82, 0xE1,
	0xA5, 0x68, 0xB3, 0xDB, 0x8F, 0x9E, 0x5E, 0x7B, 0x90, 0xF0, 0x79, 0x3F, 0x52, 0x8C, 0x61, 0x88,
	0x76, 0xAE, 0x14, 0x63, 0x19, 0x0F, 0x1D, 0xCE, 0xA1, 0x63, 0x10, 0xB2, 0xE2, 0xD7, 0x94, 0xB1,
	0x33, 0xCB, 0x28, 0x85, 0x7D, 0x9B, 0xF5, 0xF4, 0x25, 0x50, 0x9B, 0xDB, 0x35, 0xA5, 0xB0, 0x9C,
	0x09, 0x92, 0xE3, 0x31, 0x40, 0xAB, 0x4D, 0xF4, 0x35, 0xE8, 0xB3, 0x0A, 0x21, 0xC3, 0x86, 0x9C,
	0xCB, 0x29, 0xA4, 0x77, 0x57, 0xBC, 0xD8, 0xDA, 0xA5, 0x82, 0x80, 0xE8, 0xCF, 0x72, 0x81, 0xAD,
	0x2E, 0x28, 0xFF, 0xD8, 0xB6, 0xD1, 0x2B, 0x97, 0x00, 0xFF, 0xE1, 0x06, 0x44, 0x39, 0x1C, 0x4B,
	0xAB, 0x19, 0x5B, 0x4D, 0xD6, 0x3E, 0x1B, 0x5C, 0x64, 0xBB, 0x32, 0x68, 0xF5, 0x7C, 0xC9, 0x9E,
	0xE8, 0xB4, 0x29, 0x1B, 0x7F, 0x4D, 0x80, 0x80, 0x7E, 0x8B, 0x1C, 0x0A, 0xE6, 0x9A, 0xBF, 0x49,
	0x1E, 0xC5, 0xB6, 0x67, 0x7D, 0x05, 0xE4, 0x90, 0x40, 0x4B, 0xAF, 0x9B, 0x52, 0xDE, 0x17, 0x80,
	0x81, 0x56, 0xEA, 0x3A, 0x53, 0x82, 0x8C, 0x62, 0xFB, 0x96, 0x97, 0x6F, 0xC1, 0x16, 0x78, 0xD4,
	0x7B, 0xE7, 0xB9, 0x5A, 0x2A, 0xEB, 0x87, 0x68, 0x33, 0xD3, 0x31, 0x45, 0xFA, 0xFE, 0xF4, 0x1C,
	0x90, 0x86, 0x73, 0x77, 0xD9, 0xA9, 0xD1, 0x4A, 0x4A, 0xCF, 0xAE, 0x23, 0xDB, 0xF9, 0x09, 0xD8,
	0x18, 0xDC, 0x6A, 0x0D, 0xE4, 0x19, 0x8C, 0x65, 0xC6, 0x64, 0xC7, 0xDC, 0xA9, 0xE3, 0x91, 0xB1,
	0x4C, 0xC8, 0xC1, 0x9E, 0x3B, 0x7F, 0xCB, 0xA3, 0xCF, 0xDD, 0xF0, 0x1D, 0x07, 0x6E, 0xDC, 0xCE,
	0x0D, 0xCD, 0x7E, 0x1E, 0x55, 0x11, 0x8B, 0xDF, 0x3A, 0xAB, 0xB6, 0x3B, 0x6E, 0x52, 0x7F, 0xA7,
	0x00, 0xD1, 0x33, 0xBE, 0xF2, 0x9B, 0xFC, 0x4A, 0xCF, 0x9D, 0x8F, 0xC6, 0xC4, 0x7B, 0xDA, 0xE7,
	0x2A, 0x1C, 0x26, 0x6E
};


void gdrom_device::device_reset()
{
	static const uint8_t GDROM_Def_Cmd11_Reply[32] =
	{
		0x00, 0x00, 0x00, 0x00, 0x00, 0xB4, 0x19, 0x00, 0x00, 0x08, 0x53, 0x45, 0x20, 0x20, 0x20, 0x20,
		0x20, 0x20, 0x52, 0x65, 0x76, 0x20, 0x36, 0x2E, 0x34, 0x32, 0x39, 0x39, 0x30, 0x33, 0x31, 0x36
	};

	for(int i = 0;i<32;i++)
		GDROM_Cmd11_Reply[i] = GDROM_Def_Cmd11_Reply[i];

	atapi_cdrom_device::device_reset();
}

// scsicd_exec_command
//
// Execute a SCSI command.

void gdrom_device::ExecCommand()
{
	switch ( command[0] )
	{
		case 0x11: // REQ_MODE
			m_phase = SCSI_PHASE_DATAIN;
			m_status_code = SCSI_STATUS_CODE_GOOD;
			printf("REQ_MODE %02x %02x %02x %02x %02x %02x\n",
				command[0], command[1],
				command[2], command[3],
				command[4], command[5]);
//          if (SCSILengthFromUINT8( &command[ 4 ] ) < 32) return -1;
			transferOffset = command[2];
			m_transfer_length = SCSILengthFromUINT8( &command[ 4 ] );
			break;

		case 0x12: // SET_MODE
			logerror("GDROM: SET_MODE\n");
			m_phase = SCSI_PHASE_DATAOUT;
			m_status_code = SCSI_STATUS_CODE_GOOD;
			//transferOffset = command[2];
			m_transfer_length = SCSILengthFromUINT8( &command[ 4 ] );
			printf("SET_MODE %02x %02x\n",command[2],command[4]);
			break;

		case 0x30: // CD_READ
			if (command[1] & 1)
			{
				fatalerror("GDROM: MSF mode used for CD_READ, unsupported\n");
				m_transfer_length = 0;
			}
			else
			{
				m_lba = (command[2]<<16 | command[3]<<8 | command[4]) - 150;
				m_blocks = command[8]<<16 | command[9]<<8 | command[10];

				read_type = (command[1] >> 1) & 7;
				data_select = (command[1]>>4) & 0xf;

				if (read_type != 2) // mode 1
				{
					fatalerror("GDROM: Unhandled read_type %d\n", read_type);
				}

				if (data_select != 2)   // just sector data
				{
					fatalerror("GDROM: Unhandled data_select %d\n", data_select);
				}

				printf("GDROM: CD_READ at LBA %x for %d blocks (%d bytes, read type %d, data select %d)\n", m_lba, m_blocks, m_blocks * m_sector_bytes, read_type, data_select);

				if (m_num_subblocks > 1)
				{
					m_cur_subblock = m_lba % m_num_subblocks;
					m_lba /= m_num_subblocks;
				}
				else
				{
					m_cur_subblock = 0;
				}

				if (m_cdda != nullptr)
				{
					m_cdda->stop_audio();
				}

				m_phase = SCSI_PHASE_DATAIN;
				m_status_code = SCSI_STATUS_CODE_GOOD;
				m_transfer_length = m_blocks * m_sector_bytes;
			}
			break;

		// READ TOC (GD-ROM ver.)
		case 0x14:
		{
			int start_trk = command[2];// ok?
			int end_trk = cdrom_get_last_track(m_cdrom);
			int length;
			int allocation_length = SCSILengthFromUINT16( &command[ 3 ] );

			if( start_trk == 0 )
			{
				start_trk = 1;
			}
			if( start_trk == 0xaa )
			{
				end_trk = start_trk;
			}

			length = 4 + ( 8 * ( ( end_trk - start_trk ) + 1 ) );
			if( length > allocation_length )
			{
				length = allocation_length;
			}
			else if( length < 4 )
			{
				length = 4;
			}

			if (m_cdda != nullptr)
			{
				m_cdda->stop_audio();
			}

			m_phase = SCSI_PHASE_DATAIN;
			m_status_code = SCSI_STATUS_CODE_GOOD;
			m_transfer_length = length;
			break;
		}

		case 0x70:  // security check, return no data, always followed by cmd 0x71, command[1] parameter can be 0x1f or 0x9f
			m_phase = SCSI_PHASE_STATUS;
			m_status_code = SCSI_STATUS_CODE_GOOD;
			m_transfer_length = 0;
			break;

		case 0x71:
			m_phase = SCSI_PHASE_DATAIN;
			m_status_code = SCSI_STATUS_CODE_GOOD;
			m_transfer_length = sizeof(GDROM_Cmd71_Reply);
			break;

		case 0x40:
			if(command[1] & 0xf)
			{
				m_phase = SCSI_PHASE_DATAIN;
				m_status_code = SCSI_STATUS_CODE_GOOD;
				m_transfer_length = 0xe;
			}
			else
			{
				printf("command 0x40: unhandled subchannel request\n");
			}
			break;

		default:
			t10mmc::ExecCommand();
			break;
	}
}

// scsicd_read_data
//
// Read data from the device resulting from the execution of a command

void gdrom_device::ReadData( uint8_t *data, int dataLength )
{
	int i;
	uint8_t tmp_buffer[2048];

	switch ( command[0] )
	{
		case 0x11: // REQ_MODE
			printf("REQ_MODE: dataLength %d\n", dataLength);
			memcpy(data, &GDROM_Cmd11_Reply[transferOffset], (dataLength >= 32-transferOffset) ? 32-transferOffset : dataLength);
			break;

		case 0x30: // CD_READ
			logerror("GDROM: read %x dataLength, \n", dataLength);
			if ((m_cdrom) && (m_blocks))
			{
				while (dataLength > 0)
				{
					if (!cdrom_read_data(m_cdrom, m_lba, tmp_buffer, CD_TRACK_MODE1))
					{
						logerror("GDROM: CD read error!\n");
					}

					logerror("True LBA: %d, buffer half: %d\n", m_lba, m_cur_subblock * m_sector_bytes);

					memcpy(data, &tmp_buffer[m_cur_subblock * m_sector_bytes], m_sector_bytes);

					m_cur_subblock++;
					if (m_cur_subblock >= m_num_subblocks)
					{
						m_cur_subblock = 0;

						m_lba++;
						m_blocks--;
					}

					m_last_lba = m_lba;
					dataLength -= m_sector_bytes;
					data += m_sector_bytes;
				}
			}
			break;

		case 0x14: // READ TOC (GD-ROM ver.)
			/*
			    Track numbers are problematic here: 0 = lead-in, 0xaa = lead-out.
			    That makes sense in terms of how real-world CDs are referred to, but
			    our internal routines for tracks use "0" as track 1.  That probably
			    should be fixed...
			*/
			printf("GDROM: READ TOC, format = %d time=%d\n", command[2]&0xf,(command[1]>>1)&1);
			switch (command[2] & 0x0f)
			{
				case 0:     // normal
					{
						int start_trk;
						int end_trk;
						int len;
						int in_len;
						int dptr;
						uint32_t tstart;

						start_trk = command[2];
						if( start_trk == 0 )
						{
							start_trk = 1;
						}

						end_trk = cdrom_get_last_track(m_cdrom);
						len = (end_trk * 8) + 2;

						// the returned TOC DATA LENGTH must be the full amount,
						// regardless of how much we're able to pass back due to in_len
						dptr = 0;
						data[dptr++] = (len>>8) & 0xff;
						data[dptr++] = (len & 0xff);
						data[dptr++] = 1;
						data[dptr++] = end_trk;

						if( start_trk == 0xaa )
						{
							end_trk = 0xaa;
						}

						in_len = command[3]<<8 | command[4];

						for (i = start_trk; i <= end_trk; i++)
						{
							int cdrom_track = i;
							if( cdrom_track != 0xaa )
							{
								cdrom_track--;
							}

							if( dptr >= in_len )
							{
								break;
							}

							data[dptr++] = 0;
							data[dptr++] = cdrom_get_adr_control(m_cdrom, cdrom_track);
							data[dptr++] = i;
							data[dptr++] = 0;

							tstart = cdrom_get_track_start(m_cdrom, cdrom_track);
							if ((command[1]&2)>>1)
								tstart = lba_to_msf(tstart);
							data[dptr++] = (tstart>>24) & 0xff;
							data[dptr++] = (tstart>>16) & 0xff;
							data[dptr++] = (tstart>>8) & 0xff;
							data[dptr++] = (tstart & 0xff);
						}
					}
					break;
				default:
					logerror("GDROM: Unhandled READ TOC format %d\n", command[2]&0xf);
					break;
			}
			break;

		case 0x71:
			memcpy(data, &GDROM_Cmd71_Reply[0], sizeof(GDROM_Cmd71_Reply));
			if (is_real_gdrom_disc)
				data[10] = 0x1f; // needed by dimm board firmware
			break;

		case 0x40: // Get Subchannel status
			data[0] = 0; // Reserved
			data[1] = 0x15; // Audio Playback status (todo)
			data[2] = 0;
			data[3] = 0x0e; // header size
			data[4] = 0; // ?
			data[5] = 1; // Track Number
			data[6] = 1; // gap #1
			data[7] = 0; // ?
			data[8] = 0; // ?
			data[9] = 0; // ?
			data[0xa] = 0; // ?
			data[0xb] = 0; // FAD >> 16
			data[0xc] = 0; // FAD >> 8
			data[0xd] = 0x96; // FAD >> 0
			break;

		default:
			t10mmc::ReadData( data, dataLength );
			break;
	}
}

// scsicd_write_data
//
// Write data to the CD-ROM device as part of the execution of a command

void gdrom_device::WriteData( uint8_t *data, int dataLength )
{
	switch (command[ 0 ])
	{
		case 0x12: // SET_MODE
			memcpy(&GDROM_Cmd11_Reply[transferOffset], data, (dataLength >= 32-transferOffset) ? 32-transferOffset : dataLength);
			break;

		default:
			t10mmc::WriteData( data, dataLength );
			break;
	}
}

void gdrom_device::SetDevice(void *device)
{
	t10mmc::SetDevice(device);

	// try to find if the mounted chd is from an actual gd-rom disc
	if (m_cdrom)
		if (cdrom_get_toc(m_cdrom)->flags & CD_FLAG_GDROM)
			is_real_gdrom_disc = true;
}

// device type definition
DEFINE_DEVICE_TYPE(GDROM, gdrom_device, "gdrom", "GD-ROM")

gdrom_device::gdrom_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock) :
	atapi_cdrom_device(mconfig, GDROM, tag, owner, clock),
	is_real_gdrom_disc(false)
{
}

void gdrom_device::device_start()
{
	save_item(NAME(read_type));
	save_item(NAME(data_select));
	save_item(NAME(transferOffset));

	/// TODO: split identify buffer into another method as device_start() should be called after it's filled in, but the atapi_cdrom_device has it's own.
	atapi_cdrom_device::device_start();

	memset(m_identify_buffer, 0, sizeof(m_identify_buffer));

	m_identify_buffer[0] = 0x8600; // ATAPI device, cmd set 6 compliant, DRQ within 3 ms of PACKET command

	m_identify_buffer[23] = ('S' << 8) | 'E';
	m_identify_buffer[24] = (' ' << 8) | ' ';
	m_identify_buffer[25] = (' ' << 8) | ' ';
	m_identify_buffer[26] = (' ' << 8) | ' ';

	m_identify_buffer[27] = ('C' << 8) | 'D';
	m_identify_buffer[28] = ('-' << 8) | 'R';
	m_identify_buffer[29] = ('O' << 8) | 'M';
	m_identify_buffer[30] = (' ' << 8) | 'D';
	m_identify_buffer[31] = ('R' << 8) | 'I';
	m_identify_buffer[32] = ('V' << 8) | 'E';
	m_identify_buffer[33] = (' ' << 8) | ' ';
	m_identify_buffer[34] = (' ' << 8) | ' ';
	m_identify_buffer[35] = ('6' << 8) | '.';
	m_identify_buffer[36] = ('4' << 8) | '2';
	m_identify_buffer[37] = (' ' << 8) | ' ';
	m_identify_buffer[38] = (' ' << 8) | ' ';
	m_identify_buffer[39] = (' ' << 8) | ' ';
	m_identify_buffer[40] = (' ' << 8) | ' ';
	m_identify_buffer[41] = (' ' << 8) | ' ';
	m_identify_buffer[42] = (' ' << 8) | ' ';
	m_identify_buffer[43] = (' ' << 8) | ' ';
	m_identify_buffer[44] = (' ' << 8) | ' ';
	m_identify_buffer[45] = (' ' << 8) | ' ';
	m_identify_buffer[46] = (' ' << 8) | ' ';

	m_identify_buffer[49] = 0x0400; // IORDY may be disabled

	m_identify_buffer[63]=7; // multi word dma mode 0-2 supported
	m_identify_buffer[64]=1; // PIO mode 3 supported
}

void gdrom_device::process_buffer()
{
	atapi_hle_device::process_buffer();
	m_sector_number = 0x80 | GDROM_PAUSE_STATE; /// HACK: find out when this should be updated
}

void gdrom_device::signature()
{
	atapi_hle_device::signature();

	// naomi dimm board firmware needs the upper nibble to be 8 at the beginning
	if (is_real_gdrom_disc)
		m_sector_number = 0x81;
}
