sd_raw.c

/*
 * Copyright (c) 2006-2012 by Roland Riegel <feedback@roland-riegel.de>
 *
 * This file is free software; you can redistribute it and/or modify
 * it under the terms of either the GNU General Public License version 2
 * or the GNU Lesser General Public License version 2.1, both as
 * published by the Free Software Foundation.
 */

#include <string.h>
#include <avr/io.h>
#include "sd_raw.h"

/**
 * \addtogroup sd_raw MMC/SD/SDHC card raw access
 *
 * This module implements read and write access to MMC, SD
 * and SDHC cards. It serves as a low-level driver for the
 * higher level modules such as partition and file system
 * access.
 *
 * @{
 */
/**
 * \file
 * MMC/SD/SDHC raw access implementation (license: GPLv2 or LGPLv2.1)
 *
 * \author Roland Riegel
 */

/**
 * \addtogroup sd_raw_config MMC/SD configuration
 * Preprocessor defines to configure the MMC/SD support.
 */

/**
 * @}
 */

/* commands available in SPI mode */

/* CMD0: response R1 */
#define CMD_GO_IDLE_STATE 0x00
/* CMD1: response R1 */
#define CMD_SEND_OP_COND 0x01
/* CMD8: response R7 */
#define CMD_SEND_IF_COND 0x08
/* CMD9: response R1 */
#define CMD_SEND_CSD 0x09
/* CMD10: response R1 */
#define CMD_SEND_CID 0x0a
/* CMD12: response R1 */
#define CMD_STOP_TRANSMISSION 0x0c
/* CMD13: response R2 */
#define CMD_SEND_STATUS 0x0d
/* CMD16: arg0[31:0]: block length, response R1 */
#define CMD_SET_BLOCKLEN 0x10
/* CMD17: arg0[31:0]: data address, response R1 */
#define CMD_READ_SINGLE_BLOCK 0x11
/* CMD18: arg0[31:0]: data address, response R1 */
#define CMD_READ_MULTIPLE_BLOCK 0x12
/* CMD24: arg0[31:0]: data address, response R1 */
#define CMD_WRITE_SINGLE_BLOCK 0x18
/* CMD25: arg0[31:0]: data address, response R1 */
#define CMD_WRITE_MULTIPLE_BLOCK 0x19
/* CMD27: response R1 */
#define CMD_PROGRAM_CSD 0x1b
/* CMD28: arg0[31:0]: data address, response R1b */
#define CMD_SET_WRITE_PROT 0x1c
/* CMD29: arg0[31:0]: data address, response R1b */
#define CMD_CLR_WRITE_PROT 0x1d
/* CMD30: arg0[31:0]: write protect data address, response R1 */
#define CMD_SEND_WRITE_PROT 0x1e
/* CMD32: arg0[31:0]: data address, response R1 */
#define CMD_TAG_SECTOR_START 0x20
/* CMD33: arg0[31:0]: data address, response R1 */
#define CMD_TAG_SECTOR_END 0x21
/* CMD34: arg0[31:0]: data address, response R1 */
#define CMD_UNTAG_SECTOR 0x22
/* CMD35: arg0[31:0]: data address, response R1 */
#define CMD_TAG_ERASE_GROUP_START 0x23
/* CMD36: arg0[31:0]: data address, response R1 */
#define CMD_TAG_ERASE_GROUP_END 0x24
/* CMD37: arg0[31:0]: data address, response R1 */
#define CMD_UNTAG_ERASE_GROUP 0x25
/* CMD38: arg0[31:0]: stuff bits, response R1b */
#define CMD_ERASE 0x26
/* ACMD41: arg0[31:0]: OCR contents, response R1 */
#define CMD_SD_SEND_OP_COND 0x29
/* CMD42: arg0[31:0]: stuff bits, response R1b */
#define CMD_LOCK_UNLOCK 0x2a
/* CMD55: arg0[31:0]: stuff bits, response R1 */
#define CMD_APP 0x37
/* CMD58: arg0[31:0]: stuff bits, response R3 */
#define CMD_READ_OCR 0x3a
/* CMD59: arg0[31:1]: stuff bits, arg0[0:0]: crc option, response R1 */
#define CMD_CRC_ON_OFF 0x3b

/* command responses */
/* R1: size 1 byte */
#define R1_IDLE_STATE 0
#define R1_ERASE_RESET 1
#define R1_ILL_COMMAND 2
#define R1_COM_CRC_ERR 3
#define R1_ERASE_SEQ_ERR 4
#define R1_ADDR_ERR 5
#define R1_PARAM_ERR 6
/* R1b: equals R1, additional busy bytes */
/* R2: size 2 bytes */
#define R2_CARD_LOCKED 0
#define R2_WP_ERASE_SKIP 1
#define R2_ERR 2
#define R2_CARD_ERR 3
#define R2_CARD_ECC_FAIL 4
#define R2_WP_VIOLATION 5
#define R2_INVAL_ERASE 6
#define R2_OUT_OF_RANGE 7
#define R2_CSD_OVERWRITE 7
#define R2_IDLE_STATE (R1_IDLE_STATE + 8)
#define R2_ERASE_RESET (R1_ERASE_RESET + 8)
#define R2_ILL_COMMAND (R1_ILL_COMMAND + 8)
#define R2_COM_CRC_ERR (R1_COM_CRC_ERR + 8)
#define R2_ERASE_SEQ_ERR (R1_ERASE_SEQ_ERR + 8)
#define R2_ADDR_ERR (R1_ADDR_ERR + 8)
#define R2_PARAM_ERR (R1_PARAM_ERR + 8)
/* R3: size 5 bytes */
#define R3_OCR_MASK (0xffffffffUL)
#define R3_IDLE_STATE (R1_IDLE_STATE + 32)
#define R3_ERASE_RESET (R1_ERASE_RESET + 32)
#define R3_ILL_COMMAND (R1_ILL_COMMAND + 32)
#define R3_COM_CRC_ERR (R1_COM_CRC_ERR + 32)
#define R3_ERASE_SEQ_ERR (R1_ERASE_SEQ_ERR + 32)
#define R3_ADDR_ERR (R1_ADDR_ERR + 32)
#define R3_PARAM_ERR (R1_PARAM_ERR + 32)
/* Data Response: size 1 byte */
#define DR_STATUS_MASK 0x0e
#define DR_STATUS_ACCEPTED 0x05
#define DR_STATUS_CRC_ERR 0x0a
#define DR_STATUS_WRITE_ERR 0x0c

/* status bits for card types */
#define SD_RAW_SPEC_1 0
#define SD_RAW_SPEC_2 1
#define SD_RAW_SPEC_SDHC 2

#if !SD_RAW_SAVE_RAM
/* static data buffer for acceleration */
static uint8_t raw_block[512];
/* offset where the data within raw_block lies on the card */
static offset_t raw_block_address;
#if SD_RAW_WRITE_BUFFERING
/* flag to remember if raw_block was written to the card */
static uint8_t raw_block_written;
#endif
#endif

/* card type state */
static uint8_t sd_raw_card_type;

/* private helper functions */
static void sd_raw_send_byte(uint8_t b);
static uint8_t sd_raw_rec_byte();
static uint8_t sd_raw_send_command(uint8_t command, uint32_t arg);

/**
 * \ingroup sd_raw
 * Initializes memory card communication.
 *
 * \returns 0 on failure, 1 on success.
 */
uint8_t sd_raw_init()
{
    /* enable inputs for reading card status */
    configure_pin_available();
#if !defined(__CHIP_COMP__)    
	configure_pin_locked();
#endif
    /* enable outputs for MOSI, SCK, SS, input for MISO */
    configure_pin_mosi();
    configure_pin_sck();
    configure_pin_ss();
    configure_pin_miso();

    unselect_card();

    /* initialize SPI with lowest frequency; max. 400kHz during identification mode of card */
    SPCR = (0 << SPIE) | /* SPI Interrupt Enable */
           (1 << SPE)  | /* SPI Enable */
           (0 << DORD) | /* Data Order: MSB first */
           (1 << MSTR) | /* Master mode */
           (0 << CPOL) | /* Clock Polarity: SCK low when idle */
           (0 << CPHA) | /* Clock Phase: sample on rising SCK edge */
           (1 << SPR1) | /* Clock Frequency: f_OSC / 128 */
           (1 << SPR0);
    SPSR &= ~(1 << SPI2X); /* No doubled clock frequency */

    /* initialization procedure */
    sd_raw_card_type = 0;
    
    if(!sd_raw_available())
        return 0;

    /* card needs 74 cycles minimum to start up */
    for(uint8_t i = 0; i < 10; ++i)
    {
        /* wait 8 clock cycles */
        sd_raw_rec_byte();
    }

    /* address card */
    select_card();

    /* reset card */
    uint8_t response;
    for(uint16_t i = 0; ; ++i)
    {
        response = sd_raw_send_command(CMD_GO_IDLE_STATE, 0);
        if(response == (1 << R1_IDLE_STATE))
            break;

        if(i == 0x1ff)
        {
            unselect_card();
            return 0;
        }
    }

#if SD_RAW_SDHC
    /* check for version of SD card specification */
    response = sd_raw_send_command(CMD_SEND_IF_COND, 0x100 /* 2.7V - 3.6V */ | 0xaa /* test pattern */);
    if((response & (1 << R1_ILL_COMMAND)) == 0)
    {
        sd_raw_rec_byte();
        sd_raw_rec_byte();
        if((sd_raw_rec_byte() & 0x01) == 0)
            return 0; /* card operation voltage range doesn't match */
        if(sd_raw_rec_byte() != 0xaa)
            return 0; /* wrong test pattern */

        /* card conforms to SD 2 card specification */
        sd_raw_card_type |= (1 << SD_RAW_SPEC_2);
    }
    else
#endif
    {
        /* determine SD/MMC card type */
        sd_raw_send_command(CMD_APP, 0);
        response = sd_raw_send_command(CMD_SD_SEND_OP_COND, 0);
        if((response & (1 << R1_ILL_COMMAND)) == 0)
        {
            /* card conforms to SD 1 card specification */
            sd_raw_card_type |= (1 << SD_RAW_SPEC_1);
        }
        else
        {
            /* MMC card */
        }
    }

    /* wait for card to get ready */
    for(uint16_t i = 0; ; ++i)
    {
        if(sd_raw_card_type & ((1 << SD_RAW_SPEC_1) | (1 << SD_RAW_SPEC_2)))
        {
            uint32_t arg = 0;
#if SD_RAW_SDHC
            if(sd_raw_card_type & (1 << SD_RAW_SPEC_2))
                arg = 0x40000000;
#endif
            sd_raw_send_command(CMD_APP, 0);
            response = sd_raw_send_command(CMD_SD_SEND_OP_COND, arg);
        }
        else
        {
            response = sd_raw_send_command(CMD_SEND_OP_COND, 0);
        }

        if((response & (1 << R1_IDLE_STATE)) == 0)
            break;

        if(i == 0x7fff)
        {
            unselect_card();
            return 0;
        }
    }

#if SD_RAW_SDHC
    if(sd_raw_card_type & (1 << SD_RAW_SPEC_2))
    {
        if(sd_raw_send_command(CMD_READ_OCR, 0))
        {
            unselect_card();
            return 0;
        }

        if(sd_raw_rec_byte() & 0x40)
            sd_raw_card_type |= (1 << SD_RAW_SPEC_SDHC);

        sd_raw_rec_byte();
        sd_raw_rec_byte();
        sd_raw_rec_byte();
    }
#endif

    /* set block size to 512 bytes */
    if(sd_raw_send_command(CMD_SET_BLOCKLEN, 512))
    {
        unselect_card();
        return 0;
    }

    /* deaddress card */
    unselect_card();

    /* switch to highest SPI frequency possible */
    SPCR &= ~((1 << SPR1) | (1 << SPR0)); /* Clock Frequency: f_OSC / 4 */
    SPSR |= (1 << SPI2X); /* Doubled Clock Frequency: f_OSC / 2 */

#if !SD_RAW_SAVE_RAM
    /* the first block is likely to be accessed first, so precache it here */
    raw_block_address = (offset_t) -1;
#if SD_RAW_WRITE_BUFFERING
    raw_block_written = 1;
#endif
    if(!sd_raw_read(0, raw_block, sizeof(raw_block)))
        return 0;
#endif

    return 1;
}

/**
 * \ingroup sd_raw
 * Checks wether a memory card is located in the slot.
 *
 * \returns 1 if the card is available, 0 if it is not.
 */
uint8_t sd_raw_available()
{
    return get_pin_available() == 0x00;
}

#if !defined(__CHIP_COMP__)
/**
 * \ingroup sd_raw
 * Checks wether the memory card is locked for write access.
 *
 * \returns 1 if the card is locked, 0 if it is not.
 */
uint8_t sd_raw_locked()
{
    return get_pin_locked() == 0x00;
}
#endif

/**
 * \ingroup sd_raw
 * Sends a raw byte to the memory card.
 *
 * \param[in] b The byte to sent.
 * \see sd_raw_rec_byte
 */
void sd_raw_send_byte(uint8_t b)
{
    SPDR = b;
    /* wait for byte to be shifted out */
    while(!(SPSR & (1 << SPIF)));
    SPSR &= ~(1 << SPIF);
}

/**
 * \ingroup sd_raw
 * Receives a raw byte from the memory card.
 *
 * \returns The byte which should be read.
 * \see sd_raw_send_byte
 */
uint8_t sd_raw_rec_byte()
{
    /* send dummy data for receiving some */
    SPDR = 0xff;
    while(!(SPSR & (1 << SPIF)));
    SPSR &= ~(1 << SPIF);

    return SPDR;
}

/**
 * \ingroup sd_raw
 * Send a command to the memory card which responses with a R1 response (and possibly others).
 *
 * \param[in] command The command to send.
 * \param[in] arg The argument for command.
 * \returns The command answer.
 */
uint8_t sd_raw_send_command(uint8_t command, uint32_t arg)
{
    uint8_t response;

    /* wait some clock cycles */
    sd_raw_rec_byte();

    /* send command via SPI */
    sd_raw_send_byte(0x40 | command);
    sd_raw_send_byte((arg >> 24) & 0xff);
    sd_raw_send_byte((arg >> 16) & 0xff);
    sd_raw_send_byte((arg >> 8) & 0xff);
    sd_raw_send_byte((arg >> 0) & 0xff);
    switch(command)
    {
        case CMD_GO_IDLE_STATE:
           sd_raw_send_byte(0x95);
           break;
        case CMD_SEND_IF_COND:
           sd_raw_send_byte(0x87);
           break;
        default:
           sd_raw_send_byte(0xff);
           break;
    }
    
    /* receive response */
    for(uint8_t i = 0; i < 10; ++i)
    {
        response = sd_raw_rec_byte();
        if(response != 0xff)
            break;
    }

    return response;
}

/**
 * \ingroup sd_raw
 * Reads raw data from the card.
 *
 * \param[in] offset The offset from which to read.
 * \param[out] buffer The buffer into which to write the data.
 * \param[in] length The number of bytes to read.
 * \returns 0 on failure, 1 on success.
 * \see sd_raw_read_interval, sd_raw_write, sd_raw_write_interval
 */
uint8_t sd_raw_read(offset_t offset, uint8_t* buffer, uintptr_t length)
{
    offset_t block_address;
    uint16_t block_offset;
    uint16_t read_length;
    while(length > 0)
    {
        /* determine byte count to read at once */
        block_offset = offset & 0x01ff;
        block_address = offset - block_offset;
        read_length = 512 - block_offset; /* read up to block border */
        if(read_length > length)
            read_length = length;
        
#if !SD_RAW_SAVE_RAM
        /* check if the requested data is cached */
        if(block_address != raw_block_address)
#endif
        {
#if SD_RAW_WRITE_BUFFERING
            if(!sd_raw_sync())
                return 0;
#endif

            /* address card */
            select_card();

            /* send single block request */
#if SD_RAW_SDHC
            if(sd_raw_send_command(CMD_READ_SINGLE_BLOCK, (sd_raw_card_type & (1 << SD_RAW_SPEC_SDHC) ? block_address / 512 : block_address)))
#else
            if(sd_raw_send_command(CMD_READ_SINGLE_BLOCK, block_address))
#endif
            {
                unselect_card();
                return 0;
            }

            /* wait for data block (start byte 0xfe) */
            while(sd_raw_rec_byte() != 0xfe);

#if SD_RAW_SAVE_RAM
            /* read byte block */
            uint16_t read_to = block_offset + read_length;
            for(uint16_t i = 0; i < 512; ++i)
            {
                uint8_t b = sd_raw_rec_byte();
                if(i >= block_offset && i < read_to)
                    *buffer++ = b;
            }
#else
            /* read byte block */
            uint8_t* cache = raw_block;
            for(uint16_t i = 0; i < 512; ++i)
                *cache++ = sd_raw_rec_byte();
            raw_block_address = block_address;

            memcpy(buffer, raw_block + block_offset, read_length);
            buffer += read_length;
#endif
            
            /* read crc16 */
            sd_raw_rec_byte();
            sd_raw_rec_byte();
            
            /* deaddress card */
            unselect_card();

            /* let card some time to finish */
            sd_raw_rec_byte();
        }
#if !SD_RAW_SAVE_RAM
        else
        {
            /* use cached data */
            memcpy(buffer, raw_block + block_offset, read_length);
            buffer += read_length;
        }
#endif

        length -= read_length;
        offset += read_length;
    }

    return 1;
}

/**
 * \ingroup sd_raw
 * Continuously reads units of \c interval bytes and calls a callback function.
 *
 * This function starts reading at the specified offset. Every \c interval bytes,
 * it calls the callback function with the associated data buffer.
 *
 * By returning zero, the callback may stop reading.
 *
 * \note Within the callback function, you can not start another read or
 *       write operation.
 * \note This function only works if the following conditions are met:
 *       - (offset - (offset % 512)) % interval == 0
 *       - length % interval == 0
 *
 * \param[in] offset Offset from which to start reading.
 * \param[in] buffer Pointer to a buffer which is at least interval bytes in size.
 * \param[in] interval Number of bytes to read before calling the callback function.
 * \param[in] length Number of bytes to read altogether.
 * \param[in] callback The function to call every interval bytes.
 * \param[in] p An opaque pointer directly passed to the callback function.
 * \returns 0 on failure, 1 on success
 * \see sd_raw_write_interval, sd_raw_read, sd_raw_write
 */
uint8_t sd_raw_read_interval(offset_t offset, uint8_t* buffer, uintptr_t interval, uintptr_t length, sd_raw_read_interval_handler_t callback, void* p)
{
    if(!buffer || interval == 0 || length < interval || !callback)
        return 0;

#if !SD_RAW_SAVE_RAM
    while(length >= interval)
    {
        /* as reading is now buffered, we directly
         * hand over the request to sd_raw_read()
         */
        if(!sd_raw_read(offset, buffer, interval))
            return 0;
        if(!callback(buffer, offset, p))
            break;
        offset += interval;
        length -= interval;
    }

    return 1;
#else
    /* address card */
    select_card();

    uint16_t block_offset;
    uint16_t read_length;
    uint8_t* buffer_cur;
    uint8_t finished = 0;
    do
    {
        /* determine byte count to read at once */
        block_offset = offset & 0x01ff;
        read_length = 512 - block_offset;
        
        /* send single block request */
#if SD_RAW_SDHC
        if(sd_raw_send_command(CMD_READ_SINGLE_BLOCK, (sd_raw_card_type & (1 << SD_RAW_SPEC_SDHC) ? offset / 512 : offset - block_offset)))
#else
        if(sd_raw_send_command(CMD_READ_SINGLE_BLOCK, offset - block_offset))
#endif
        {
            unselect_card();
            return 0;
        }

        /* wait for data block (start byte 0xfe) */
        while(sd_raw_rec_byte() != 0xfe);

        /* read up to the data of interest */
        for(uint16_t i = 0; i < block_offset; ++i)
            sd_raw_rec_byte();

        /* read interval bytes of data and execute the callback */
        do
        {
            if(read_length < interval || length < interval)
                break;

            buffer_cur = buffer;
            for(uint16_t i = 0; i < interval; ++i)
                *buffer_cur++ = sd_raw_rec_byte();

            if(!callback(buffer, offset + (512 - read_length), p))
            {
                finished = 1;
                break;
            }

            read_length -= interval;
            length -= interval;

        } while(read_length > 0 && length > 0);
        
        /* read rest of data block */
        while(read_length-- > 0)
            sd_raw_rec_byte();
        
        /* read crc16 */
        sd_raw_rec_byte();
        sd_raw_rec_byte();

        if(length < interval)
            break;

        offset = offset - block_offset + 512;

    } while(!finished);
    
    /* deaddress card */
    unselect_card();

    /* let card some time to finish */
    sd_raw_rec_byte();

    return 1;
#endif
}

#if DOXYGEN || SD_RAW_WRITE_SUPPORT
/**
 * \ingroup sd_raw
 * Writes raw data to the card.
 *
 * \note If write buffering is enabled, you might have to
 *       call sd_raw_sync() before disconnecting the card
 *       to ensure all remaining data has been written.
 *
 * \param[in] offset The offset where to start writing.
 * \param[in] buffer The buffer containing the data to be written.
 * \param[in] length The number of bytes to write.
 * \returns 0 on failure, 1 on success.
 * \see sd_raw_write_interval, sd_raw_read, sd_raw_read_interval
 */
uint8_t sd_raw_write(offset_t offset, const uint8_t* buffer, uintptr_t length)
{
    if(sd_raw_locked())
        return 0;

    offset_t block_address;
    uint16_t block_offset;
    uint16_t write_length;
    while(length > 0)
    {
        /* determine byte count to write at once */
        block_offset = offset & 0x01ff;
        block_address = offset - block_offset;
        write_length = 512 - block_offset; /* write up to block border */
        if(write_length > length)
            write_length = length;
        
        /* Merge the data to write with the content of the block.
         * Use the cached block if available.
         */
        if(block_address != raw_block_address)
        {
#if SD_RAW_WRITE_BUFFERING
            if(!sd_raw_sync())
                return 0;
#endif

            if(block_offset || write_length < 512)
            {
                if(!sd_raw_read(block_address, raw_block, sizeof(raw_block)))
                    return 0;
            }
            raw_block_address = block_address;
        }

        if(buffer != raw_block)
        {
            memcpy(raw_block + block_offset, buffer, write_length);

#if SD_RAW_WRITE_BUFFERING
            raw_block_written = 0;

            if(length == write_length)
                return 1;
#endif
        }

        /* address card */
        select_card();

        /* send single block request */
#if SD_RAW_SDHC
        if(sd_raw_send_command(CMD_WRITE_SINGLE_BLOCK, (sd_raw_card_type & (1 << SD_RAW_SPEC_SDHC) ? block_address / 512 : block_address)))
#else
        if(sd_raw_send_command(CMD_WRITE_SINGLE_BLOCK, block_address))
#endif
        {
            unselect_card();
            return 0;
        }

        /* send start byte */
        sd_raw_send_byte(0xfe);

        /* write byte block */
        uint8_t* cache = raw_block;
        for(uint16_t i = 0; i < 512; ++i)
            sd_raw_send_byte(*cache++);

        /* write dummy crc16 */
        sd_raw_send_byte(0xff);
        sd_raw_send_byte(0xff);

        /* wait while card is busy */
        while(sd_raw_rec_byte() != 0xff);
        sd_raw_rec_byte();

        /* deaddress card */
        unselect_card();

        buffer += write_length;
        offset += write_length;
        length -= write_length;

#if SD_RAW_WRITE_BUFFERING
        raw_block_written = 1;
#endif
    }

    return 1;
}
#endif

#if DOXYGEN || SD_RAW_WRITE_SUPPORT
/**
 * \ingroup sd_raw
 * Writes a continuous data stream obtained from a callback function.
 *
 * This function starts writing at the specified offset. To obtain the
 * next bytes to write, it calls the callback function. The callback fills the
 * provided data buffer and returns the number of bytes it has put into the buffer.
 *
 * By returning zero, the callback may stop writing.
 *
 * \param[in] offset Offset where to start writing.
 * \param[in] buffer Pointer to a buffer which is used for the callback function.
 * \param[in] length Number of bytes to write in total. May be zero for endless writes.
 * \param[in] callback The function used to obtain the bytes to write.
 * \param[in] p An opaque pointer directly passed to the callback function.
 * \returns 0 on failure, 1 on success
 * \see sd_raw_read_interval, sd_raw_write, sd_raw_read
 */
uint8_t sd_raw_write_interval(offset_t offset, uint8_t* buffer, uintptr_t length, sd_raw_write_interval_handler_t callback, void* p)
{
#if SD_RAW_SAVE_RAM
    #error "SD_RAW_WRITE_SUPPORT is not supported together with SD_RAW_SAVE_RAM"
#endif

    if(!buffer || !callback)
        return 0;

    uint8_t endless = (length == 0);
    while(endless || length > 0)
    {
        uint16_t bytes_to_write = callback(buffer, offset, p);
        if(!bytes_to_write)
            break;
        if(!endless && bytes_to_write > length)
            return 0;

        /* as writing is always buffered, we directly
         * hand over the request to sd_raw_write()
         */
        if(!sd_raw_write(offset, buffer, bytes_to_write))
            return 0;

        offset += bytes_to_write;
        length -= bytes_to_write;
    }

    return 1;
}
#endif

#if DOXYGEN || SD_RAW_WRITE_SUPPORT
/**
 * \ingroup sd_raw
 * Writes the write buffer's content to the card.
 *
 * \note When write buffering is enabled, you should
 *       call this function before disconnecting the
 *       card to ensure all remaining data has been
 *       written.
 *
 * \returns 0 on failure, 1 on success.
 * \see sd_raw_write
 */
uint8_t sd_raw_sync()
{
#if SD_RAW_WRITE_BUFFERING
    if(raw_block_written)
        return 1;
    if(!sd_raw_write(raw_block_address, raw_block, sizeof(raw_block)))
        return 0;
    raw_block_written = 1;
#endif
    return 1;
}
#endif

/**
 * \ingroup sd_raw
 * Reads informational data from the card.
 *
 * This function reads and returns the card's registers
 * containing manufacturing and status information.
 *
 * \note: The information retrieved by this function is
 *        not required in any way to operate on the card,
 *        but it might be nice to display some of the data
 *        to the user.
 *
 * \param[in] info A pointer to the structure into which to save the information.
 * \returns 0 on failure, 1 on success.
 */
uint8_t sd_raw_get_info(struct sd_raw_info* info)
{
    if(!info || !sd_raw_available())
        return 0;

    memset(info, 0, sizeof(*info));

    select_card();

    /* read cid register */
    if(sd_raw_send_command(CMD_SEND_CID, 0))
    {
        unselect_card();
        return 0;
    }
    while(sd_raw_rec_byte() != 0xfe);
    for(uint8_t i = 0; i < 18; ++i)
    {
        uint8_t b = sd_raw_rec_byte();

        switch(i)
        {
            case 0:
                info->manufacturer = b;
                break;
            case 1:
            case 2:
                info->oem[i - 1] = b;
                break;
            case 3:
            case 4:
            case 5:
            case 6:
            case 7:
                info->product[i - 3] = b;
                break;
            case 8:
                info->revision = b;
                break;
            case 9:
            case 10:
            case 11:
            case 12:
                info->serial |= (uint32_t) b << ((12 - i) * 8);
                break;
            case 13:
                info->manufacturing_year = b << 4;
                break;
            case 14:
                info->manufacturing_year |= b >> 4;
                info->manufacturing_month = b & 0x0f;
                break;
        }
    }

    /* read csd register */
    uint8_t csd_read_bl_len = 0;
    uint8_t csd_c_size_mult = 0;
#if SD_RAW_SDHC
    uint16_t csd_c_size = 0;
#else
    uint32_t csd_c_size = 0;
#endif
    uint8_t csd_structure = 0;
    if(sd_raw_send_command(CMD_SEND_CSD, 0))
    {
        unselect_card();
        return 0;
    }
    while(sd_raw_rec_byte() != 0xfe);
    for(uint8_t i = 0; i < 18; ++i)
    {
        uint8_t b = sd_raw_rec_byte();

        if(i == 0)
        {
            csd_structure = b >> 6;
        }
        else if(i == 14)
        {
            if(b & 0x40)
                info->flag_copy = 1;
            if(b & 0x20)
                info->flag_write_protect = 1;
            if(b & 0x10)
                info->flag_write_protect_temp = 1;
            info->format = (b & 0x0c) >> 2;
        }
        else
        {
#if SD_RAW_SDHC
            if(csd_structure == 0x01)
            {
                switch(i)
                {
                    case 7:
                        b &= 0x3f;
                    case 8:
                    case 9:
                        csd_c_size <<= 8;
                        csd_c_size |= b;
                        break;
                }
                if(i == 9)
                {
                    ++csd_c_size;
                    info->capacity = (offset_t) csd_c_size * 512 * 1024;
                }
            }
            else if(csd_structure == 0x00)
#endif
            {
                switch(i)
                {
                    case 5:
                        csd_read_bl_len = b & 0x0f;
                        break;
                    case 6:
                        csd_c_size = b & 0x03;
                        csd_c_size <<= 8;
                        break;
                    case 7:
                        csd_c_size |= b;
                        csd_c_size <<= 2;
                        break;
                    case 8:
                        csd_c_size |= b >> 6;
                        ++csd_c_size;
                        break;
                    case 9:
                        csd_c_size_mult = b & 0x03;
                        csd_c_size_mult <<= 1;
                        break;
                    case 10:
                        csd_c_size_mult |= b >> 7;

                        info->capacity = (uint32_t) csd_c_size << (csd_c_size_mult + csd_read_bl_len + 2);
                        break;
                }
            }
        }
    }

    unselect_card();

    return 1;
}