/*------------------------------------------------------------------------/
/  MMCv3/SDv1/SDv2 (in SPI mode) control module
/-------------------------------------------------------------------------/
/
/  Copyright (C) 2013, ChaN, all right reserved.
/
/ * This software is a free software and there is NO WARRANTY.
/ * No restriction on use. You can use, modify and redistribute it for
/   personal, non-profit or commercial products UNDER YOUR RESPONSIBILITY.
/ * Redistributions of source code must retain the above copyright notice.
/
/-------------------------------------------------------------------------*/


/*
 * This file was modified from a sample available from the FatFs
 * web site. It was modified to work with a Olimex STM32-P103
 * evaluation board.
 *
 */
#include "diskio.h"
#include "stm32f4xx.h"                                /* STM32 registers               */
#include "boot.h"


/*--------------------------------------------------------------------------

   Macro Definitions

---------------------------------------------------------------------------*/
/* MMC card type flags (MMC_GET_TYPE) */
#define CT_MMC		0x01		/* MMC ver 3 */
#define CT_SD1		0x02		/* SD ver 1 */
#define CT_SD2		0x04		/* SD ver 2 */
#define CT_SDC		(CT_SD1|CT_SD2)	/* SD */
#define CT_BLOCK	0x08		/* Block addressing */


/*--------------------------------------------------------------------------

   Module Private Functions

---------------------------------------------------------------------------*/

/* Definitions for MMC/SDC command */
#define CMD0   (0)			/* GO_IDLE_STATE */
#define CMD1   (1)			/* SEND_OP_COND */
#define ACMD41 (41|0x80)	/* SEND_OP_COND (SDC) */
#define CMD8   (8)			/* SEND_IF_COND */
#define CMD9   (9)			/* SEND_CSD */
#define CMD10  (10)			/* SEND_CID */
#define CMD12  (12)			/* STOP_TRANSMISSION */
#define ACMD13 (13|0x80)	/* SD_STATUS (SDC) */
#define CMD16  (16)			/* SET_BLOCKLEN */
#define CMD17  (17)			/* READ_SINGLE_BLOCK */
#define CMD18  (18)			/* READ_MULTIPLE_BLOCK */
#define CMD23  (23)			/* SET_BLOCK_COUNT */
#define ACMD23 (23|0x80)	/* SET_WR_BLK_ERASE_COUNT (SDC) */
#define CMD24  (24)			/* WRITE_BLOCK */
#define CMD25  (25)			/* WRITE_MULTIPLE_BLOCK */
#define CMD41  (41)			/* SEND_OP_COND (ACMD) */
#define CMD55  (55)			/* APP_CMD */
#define CMD58  (58)			/* READ_OCR */


/* Control signals (Platform dependent) */
#define CS_LOW()	  GPIO_ResetBits(GPIOB, GPIO_Pin_12)  /* MMC CS = L */
#define	CS_HIGH()	  GPIO_SetBits(GPIOB, GPIO_Pin_12)  	/* MMC CS = H */



#define	FCLK_SLOW()			/* Set slow clock (100k-400k) */
#define	FCLK_FAST()	set_max_speed()	/* Set fast clock (depends on the CSD) */

static volatile
DSTATUS Stat = STA_NOINIT;	/* Disk status */

static
UINT CardType;


/*-----------------------------------------------------------------------*/
/* Send 80 or so clock transitions with CS and DI held high. This is     */
/* required after card power up to get it into SPI mode                  */
/*-----------------------------------------------------------------------*/
static
void send_initial_clock_train(void)
{
  GPIO_InitTypeDef GPIO_InitStructure;
  unsigned int i;

  /* Ensure CS is held high. */
  CS_HIGH();

  /* Switch the SSI TX line to a GPIO and drive it high too. */
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_15;
  GPIO_Init(GPIOB, &GPIO_InitStructure);
  GPIO_SetBits(GPIOB, GPIO_Pin_15);

  /* Send 10 bytes over the SSI. This causes the clock to wiggle the */
  /* required number of times. */
  for(i = 0 ; i < 10 ; i++)
  {
    /* Loop while DR register in not empty */
    while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_TXE) == RESET) { ; }

    /* Send byte through the SPI peripheral */
    SPI_I2S_SendData(SPI2, 0xff);

    /* Wait to receive a byte */
    while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_RXNE) == RESET) { ; }
  }

  /* Revert to hardware control of the SSI TX line. */
  GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_15;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_DOWN;
  GPIO_Init(GPIOB, &GPIO_InitStructure);
}


/*-----------------------------------------------------------------------*/
/* Power Control  (Platform dependent)                                   */
/*-----------------------------------------------------------------------*/
/* When the target system does not support socket power control, there   */
/* is nothing to do in these functions.                                  */

static
void power_on (void)
{
  SPI_InitTypeDef  SPI_InitStructure;
  GPIO_InitTypeDef GPIO_InitStructure;

  /*
   * This doesn't really turn the power on, but initializes the
   * SSI port and pins needed to talk to the card.
   */

  /* Enable GPIO clock for SPI pins */
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);
  /* Enable SPI clock, SPI2: APB1 */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_SPI2, ENABLE);
  /* Configure I/O for Chip select (PB12) */
  GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_12;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_Init(GPIOB, &GPIO_InitStructure);

  /* De-select the Card: Chip Select high */
  GPIO_SetBits(GPIOB, GPIO_Pin_12);

  /* Configure SPI pins: SCK (PB13) and MOSI (PB15) with default alternate function (not re-mapped) push-pull */
  GPIO_PinAFConfig(GPIOB, GPIO_PinSource13, GPIO_AF_SPI2);
  GPIO_PinAFConfig(GPIOB, GPIO_PinSource14, GPIO_AF_SPI2);
  GPIO_PinAFConfig(GPIOB, GPIO_PinSource15, GPIO_AF_SPI2);
  GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_DOWN;
  GPIO_Init(GPIOB, &GPIO_InitStructure);

  /* SPI configuration */
  SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
  SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
  SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;
  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_128; // 168MHz/4/128=328kHz < 400kHz
  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
  SPI_InitStructure.SPI_CRCPolynomial = 7;

  SPI_Init(SPI2, &SPI_InitStructure);
  SPI_CalculateCRC(SPI2, DISABLE);
  SPI_Cmd(SPI2, ENABLE);

  /* Set DI and CS high and apply more than 74 pulses to SCLK for the card */
  /* to be able to accept a native command. */
  send_initial_clock_train();
}

// set the SSI speed to the max setting
static
void set_max_speed(void)
{
  SPI_InitTypeDef  SPI_InitStructure;

  /* Disable the SPI system */
  SPI_Cmd(SPI2, DISABLE);

  /* MMC/SDC can work at the clock frequency up to 20/25MHz so pick a speed close to
   * this but not higher
   */
  SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
  SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
  SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;
  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_2; // 168MHz/4/2=21MHz < 25MHz
  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
  SPI_InitStructure.SPI_CRCPolynomial = 7;
  SPI_Init(SPI2, &SPI_InitStructure);
  SPI_CalculateCRC(SPI2, DISABLE);

  /* Enable the SPI system */
  SPI_Cmd(SPI2, ENABLE);
}

static
void power_off (void)
{
	Stat |= STA_NOINIT;	/* Force uninitialized */
}


/*-----------------------------------------------------------------------*/
/* Transmit/Receive data to/from MMC via SPI  (Platform dependent)       */
/*-----------------------------------------------------------------------*/

static
BYTE xchg_spi (BYTE dat)
{
  /* Send byte through the SPI peripheral */
  SPI_I2S_SendData(SPI2, dat);

  /* Wait to receive a byte */
  while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_RXNE) == RESET) { ; }

  /* Return the byte read from the SPI bus */
  return (BYTE)SPI_I2S_ReceiveData(SPI2);
}

static
void rcvr_spi_m (BYTE *dst)
{
    *dst = xchg_spi(0xFF);
}


/*-----------------------------------------------------------------------*/
/* Wait for card ready                                                   */
/*-----------------------------------------------------------------------*/

static
int wait_ready (void)
{
	BYTE d;
  DWORD timeOutTime;

  /* set timeout for 500 ms from now */
  timeOutTime = TimerGet() + 500;

	do {
		d = xchg_spi(0xFF);
	} while ((d != 0xFF) && (TimerGet() < timeOutTime));

	return (d == 0xFF) ? 1 : 0;
}


/*-----------------------------------------------------------------------*/
/* Deselect the card and release SPI bus                                 */
/*-----------------------------------------------------------------------*/

static
void deselect (void)
{
	CS_HIGH();
	xchg_spi(0xFF);		/* Dummy clock (force DO hi-z for multiple slave SPI) */
}



/*-----------------------------------------------------------------------*/
/* Select the card and wait ready                                        */
/*-----------------------------------------------------------------------*/

static
int select (void)	/* 1:Successful, 0:Timeout */
{
	CS_LOW();
	xchg_spi(0xFF);		/* Dummy clock (force DO enabled) */

	if (wait_ready()) return 1;	/* OK */
	deselect();
	return 0;	/* Timeout */
}



/*-----------------------------------------------------------------------*/
/* Receive a data packet from MMC                                        */
/*-----------------------------------------------------------------------*/

static
int rcvr_datablock (	/* 1:OK, 0:Failed */
	BYTE *buff,			/* Data buffer to store received data */
	UINT btr			/* Byte count (must be multiple of 4) */
)
{
	BYTE token;
  DWORD timeOutTime;

  /* set timeout for 100 ms from now */
  timeOutTime = TimerGet() + 100;

	do {							/* Wait for data packet in timeout of 100ms */
		token = xchg_spi(0xFF);
	} while ((token == 0xFF) && (TimerGet() < timeOutTime));

	if(token != 0xFE) return 0;		/* If not valid data token, retutn with error */

    do {                            /* Receive the data block into buffer */
        rcvr_spi_m(buff++);
        rcvr_spi_m(buff++);
    } while (btr -= 2);
	xchg_spi(0xFF);					/* Discard CRC */
	xchg_spi(0xFF);

	return 1;						/* Return with success */
}



/*-----------------------------------------------------------------------*/
/* Send a data packet to MMC                                             */
/*-----------------------------------------------------------------------*/

static
int xmit_datablock (	/* 1:OK, 0:Failed */
	const BYTE *buff,	/* 512 byte data block to be transmitted */
	BYTE token			/* Data token */
)
{
    BYTE resp;
    UINT wc;


	if (!wait_ready()) return 0;

	xchg_spi(token);		/* Xmit a token */
	if (token != 0xFD) {	/* Not StopTran token */
        wc = 512;
        do {                            /* Xmit the 512 byte data block to MMC */
            xchg_spi(*buff++);
            xchg_spi(*buff++);
        } while (wc -= 2);
		xchg_spi(0xFF);				/* CRC (Dummy) */
		xchg_spi(0xFF);
		resp = xchg_spi(0xFF);		/* Receive a data response */
		if ((resp & 0x1F) != 0x05)	/* If not accepted, return with error */
			return 0;
	}

	return 1;
}



/*-----------------------------------------------------------------------*/
/* Send a command packet to MMC                                          */
/*-----------------------------------------------------------------------*/

static
BYTE send_cmd (
	BYTE cmd,		/* Command byte */
	DWORD arg		/* Argument */
)
{
	BYTE n, res;


	if (cmd & 0x80) {	/* ACMD<n> is the command sequense of CMD55-CMD<n> */
		cmd &= 0x7F;
		res = send_cmd(CMD55, 0);
		if (res > 1) return res;
	}

	/* Select the card and wait for ready */
	deselect();
	if (!select()) return 0xFF;

	/* Send command packet */
	xchg_spi(0x40 | cmd);			/* Start + Command index */
	xchg_spi((BYTE)(arg >> 24));	/* Argument[31..24] */
	xchg_spi((BYTE)(arg >> 16));	/* Argument[23..16] */
	xchg_spi((BYTE)(arg >> 8));		/* Argument[15..8] */
	xchg_spi((BYTE)arg);			/* Argument[7..0] */
	n = 0x01;						/* Dummy CRC + Stop */
	if (cmd == CMD0) n = 0x95;		/* Valid CRC for CMD0(0) + Stop */
	if (cmd == CMD8) n = 0x87;		/* Valid CRC for CMD8(0x1AA) + Stop */
	xchg_spi(n);

	/* Receive command response */
	if (cmd == CMD12) xchg_spi(0xFF);	/* Skip a stuff byte on stop to read */
	n = 10;							/* Wait for a valid response in timeout of 10 attempts */
	do
		res = xchg_spi(0xFF);
	while ((res & 0x80) && --n);

	return res;			/* Return with the response value */
}



/*--------------------------------------------------------------------------

   Public Functions

---------------------------------------------------------------------------*/


/*-----------------------------------------------------------------------*/
/* Initialize Disk Drive                                                 */
/*-----------------------------------------------------------------------*/

DSTATUS disk_initialize (
	BYTE pdrv		/* Physical drive nmuber (0) */
)
{
	BYTE n, cmd, ty, ocr[4];
  DWORD timeOutTime;


	if (pdrv) return STA_NOINIT;		/* Supports only single drive */
	if (Stat & STA_NODISK) return Stat;	/* No card in the socket */

    power_on();                            /* Force socket power on */

     CS_LOW();                /* CS = L */

	ty = 0;
	if (send_cmd(CMD0, 0) == 1) {			/* Enter Idle state */
    timeOutTime = TimerGet() + 1000; /* Initialization timeout of 1000 msec */

		if (send_cmd(CMD8, 0x1AA) == 1) {	/* SDv2? */
			for (n = 0; n < 4; n++) ocr[n] = xchg_spi(0xFF);			/* Get trailing return value of R7 resp */
			if (ocr[2] == 0x01 && ocr[3] == 0xAA) {				/* The card can work at vdd range of 2.7-3.6V */
				while ((TimerGet() < timeOutTime) && send_cmd(ACMD41, 0x40000000));	/* Wait for leaving idle state (ACMD41 with HCS bit) */
				if ((TimerGet() < timeOutTime) && send_cmd(CMD58, 0) == 0) {			/* Check CCS bit in the OCR */
					for (n = 0; n < 4; n++) ocr[n] = xchg_spi(0xFF);
					ty = (ocr[0] & 0x40) ? CT_SD2|CT_BLOCK : CT_SD2;	/* SDv2 */
				}
			}
		} else {							/* SDv1 or MMCv3 */
			if (send_cmd(ACMD41, 0) <= 1) 	{
				ty = CT_SD1; cmd = ACMD41;	/* SDv1 */
			} else {
				ty = CT_MMC; cmd = CMD1;	/* MMCv3 */
			}
			while ((TimerGet() < timeOutTime) && send_cmd(cmd, 0));		/* Wait for leaving idle state */
			if (!(TimerGet() < timeOutTime) || send_cmd(CMD16, 512) != 0)	/* Set read/write block length to 512 */
				ty = 0;
		}
	}
	CardType = ty;
	deselect();

	if (ty) {			/* Initialization succeded */
		Stat &= ~STA_NOINIT;	/* Clear STA_NOINIT */
		FCLK_FAST();
	} else {			/* Initialization failed */
		power_off();
	}

	return Stat;
}



/*-----------------------------------------------------------------------*/
/* Get Disk Status                                                       */
/*-----------------------------------------------------------------------*/

DSTATUS disk_status (
	BYTE pdrv		/* Physical drive nmuber (0) */
)
{
	if (pdrv) return STA_NOINIT;	/* Supports only single drive */
	return Stat;
}



/*-----------------------------------------------------------------------*/
/* Read Sector(s)                                                        */
/*-----------------------------------------------------------------------*/

DRESULT disk_read (
	BYTE pdrv,		/* Physical drive nmuber to identify the drive */
	BYTE *buff,		/* Data buffer to store read data */
	DWORD sector,	/* Sector address in LBA */
	UINT count		/* Number of sectors to read */
)
{
	if (pdrv || !count) return RES_PARERR;
	if (Stat & STA_NOINIT) return RES_NOTRDY;

	if (!(CardType & CT_BLOCK)) sector *= 512;	/* Convert to byte address if needed */

	if (count == 1) {		/* Single block read */
		if ((send_cmd(CMD17, sector) == 0)	/* READ_SINGLE_BLOCK */
			&& rcvr_datablock(buff, 512))
			count = 0;
	}
	else {				/* Multiple block read */
		if (send_cmd(CMD18, sector) == 0) {	/* READ_MULTIPLE_BLOCK */
			do {
				if (!rcvr_datablock(buff, 512)) break;
				buff += 512;
			} while (--count);
			send_cmd(CMD12, 0);				/* STOP_TRANSMISSION */
		}
	}
	deselect();

	return count ? RES_ERROR : RES_OK;
}



/*-----------------------------------------------------------------------*/
/* Write Sector(s)                                                       */
/*-----------------------------------------------------------------------*/

DRESULT disk_write (
	BYTE pdrv,			/* Physical drive nmuber to identify the drive */
	const BYTE *buff,	/* Data to be written */
	DWORD sector,		/* Sector address in LBA */
	UINT count			/* Number of sectors to write */
)
{
	if (pdrv || !count) return RES_PARERR;
	if (Stat & STA_NOINIT) return RES_NOTRDY;
	if (Stat & STA_PROTECT) return RES_WRPRT;

	if (!(CardType & CT_BLOCK)) sector *= 512;	/* Convert to byte address if needed */

	if (count == 1) {		/* Single block write */
		if ((send_cmd(CMD24, sector) == 0)	/* WRITE_BLOCK */
			&& xmit_datablock(buff, 0xFE))
			count = 0;
	}
	else {				/* Multiple block write */
		if (CardType & CT_SDC) send_cmd(ACMD23, count);
		if (send_cmd(CMD25, sector) == 0) {	/* WRITE_MULTIPLE_BLOCK */
			do {
				if (!xmit_datablock(buff, 0xFC)) break;
				buff += 512;
			} while (--count);
			if (!xmit_datablock(0, 0xFD))	/* STOP_TRAN token */
				count = 1;
		}
	}
	deselect();

	return count ? RES_ERROR : RES_OK;
}



/*-----------------------------------------------------------------------*/
/* Miscellaneous Functions                                               */
/*-----------------------------------------------------------------------*/

DRESULT disk_ioctl (
	BYTE pdrv,		/* Physical drive nmuber (0) */
	BYTE cmd,		/* Control code */
	void *buff		/* Buffer to send/receive data block */
)
{
	DRESULT res;
	BYTE n, csd[16], *ptr = buff;
	DWORD csz;


	if (pdrv) return RES_PARERR;
	if (Stat & STA_NOINIT) return RES_NOTRDY;

	res = RES_ERROR;
	switch (cmd) {
	case CTRL_SYNC :	/* Flush write-back cache, Wait for end of internal process */
		if (select()) res = RES_OK;
		break;

	case GET_SECTOR_COUNT :	/* Get number of sectors on the disk (WORD) */
		if ((send_cmd(CMD9, 0) == 0) && rcvr_datablock(csd, 16)) {
			if ((csd[0] >> 6) == 1) {	/* SDv2? */
				csz = csd[9] + ((WORD)csd[8] << 8) + ((DWORD)(csd[7] & 63) << 16) + 1;
				*(DWORD*)buff = csz << 10;
			} else {					/* SDv1 or MMCv3 */
				n = (csd[5] & 15) + ((csd[10] & 128) >> 7) + ((csd[9] & 3) << 1) + 2;
				csz = (csd[8] >> 6) + ((WORD)csd[7] << 2) + ((WORD)(csd[6] & 3) << 10) + 1;
				*(DWORD*)buff = csz << (n - 9);
			}
			res = RES_OK;
		}
		break;

	case GET_BLOCK_SIZE :	/* Get erase block size in unit of sectors (DWORD) */
		if (CardType & CT_SD2) {	/* SDv2? */
			if (send_cmd(ACMD13, 0) == 0) {		/* Read SD status */
				xchg_spi(0xFF);
				if (rcvr_datablock(csd, 16)) {				/* Read partial block */
					for (n = 64 - 16; n; n--) xchg_spi(0xFF);	/* Purge trailing data */
					*(DWORD*)buff = 16UL << (csd[10] >> 4);
					res = RES_OK;
				}
			}
		} else {					/* SDv1 or MMCv3 */
			if ((send_cmd(CMD9, 0) == 0) && rcvr_datablock(csd, 16)) {	/* Read CSD */
				if (CardType & CT_SD1) {	/* SDv1 */
					*(DWORD*)buff = (((csd[10] & 63) << 1) + ((WORD)(csd[11] & 128) >> 7) + 1) << ((csd[13] >> 6) - 1);
				} else {					/* MMCv3 */
					*(DWORD*)buff = ((WORD)((csd[10] & 124) >> 2) + 1) * (((csd[11] & 3) << 3) + ((csd[11] & 224) >> 5) + 1);
				}
				res = RES_OK;
			}
		}
		break;

	case MMC_GET_TYPE :		/* Get card type flags (1 byte) */
		*ptr = CardType;
		res = RES_OK;
		break;

	case MMC_GET_CSD :	/* Receive CSD as a data block (16 bytes) */
		if ((send_cmd(CMD9, 0) == 0)	/* READ_CSD */
			&& rcvr_datablock(buff, 16))
			res = RES_OK;
		break;

	case MMC_GET_CID :	/* Receive CID as a data block (16 bytes) */
		if ((send_cmd(CMD10, 0) == 0)	/* READ_CID */
			&& rcvr_datablock(buff, 16))
			res = RES_OK;
		break;

	case MMC_GET_OCR :	/* Receive OCR as an R3 resp (4 bytes) */
		if (send_cmd(CMD58, 0) == 0) {	/* READ_OCR */
			for (n = 0; n < 4; n++)
				*((BYTE*)buff+n) = xchg_spi(0xFF);
			res = RES_OK;
		}
		break;

	case MMC_GET_SDSTAT :	/* Receive SD status as a data block (64 bytes) */
		if ((CardType & CT_SD2) && send_cmd(ACMD13, 0) == 0) {	/* SD_STATUS */
			xchg_spi(0xFF);
			if (rcvr_datablock(buff, 64))
				res = RES_OK;
		}
		break;

	default:
		res = RES_PARERR;
	}

	deselect();

	return res;
}