SD Card

VFS driver for accessing SD cards over the SCIF port. More...

Files
file	sd.h
	Block-level access to an SD card attached to the SCIF port.

Functions
uint8	sd_crc7 (const uint8 *data, int size, uint8 crc)
	Calculate a SD/MMC-style CRC over a block of data.
int	sd_init (void)
	Initialize the SD card for use.
int	sd_shutdown (void)
	Shut down SD card support.
int	sd_read_blocks (uint32 block, size_t count, uint8 *buf)
	Read one or more blocks from the SD card.
int	sd_write_blocks (uint32 block, size_t count, const uint8 *buf)
	Write one or more blocks to the SD card.
uint64	sd_get_size (void)
	Retrieve the size of the SD card.
int	sd_blockdev_for_partition (int partition, kos_blockdev_t *rv, uint8 *partition_type)
	Get a block device for a given partition on the SD card.

Detailed Description

VFS driver for accessing SD cards over the SCIF port.

Function Documentation

sd_blockdev_for_partition()

int sd_blockdev_for_partition	(	int	partition,
		kos_blockdev_t *	rv,
		uint8 *	partition_type
	)

Get a block device for a given partition on the SD card.

This function creates a block device descriptor for the given partition on the attached SD card. This block device is used to interface with various filesystems on the device.

Parameters

partition	The partition number (0-3) to use.
rv	Used to return the block device. Must be non-NULL.
partition_type	Used to return the partition type. Must be non-NULL.

Return values

0	On success.
-1	On error, errno will be set as appropriate.

Error Conditions:

ENXIO - SD card support was not initialized
EIO - an I/O error occurred in reading data
EINVAL - invalid partition number was given
EFAULT - rv or partition_type was NULL
ENOENT - no MBR found
ENOENT - no partition at the specified position
ENOMEM - out of memory

Note

This interface currently only supports MBR-formatted SD cards. There is currently no support for GPT partition tables.

sd_crc7()

uint8 sd_crc7	(	const uint8 *	data,
		int	size,
		uint8	crc
	)

Calculate a SD/MMC-style CRC over a block of data.

This function calculates a 7-bit CRC over a given block of data. The polynomial of this CRC is x^7 + x^3 + 1. The CRC is shifted into the upper 7 bits of the return value, so bit 0 should always be 0.

Parameters

data	The block of data to calculate the CRC over.
size	The number of bytes in the block of data.
crc	The starting value of the calculation. If you're passing in a full block, this will probably be 0.

Returns

The calculated CRC.

sd_get_size()

uint64 sd_get_size

(

void

)

Retrieve the size of the SD card.

This function reads the size of the SD card from the card's CSD register. This is the raw size of the card, not its formatted capacity. To get the number of blocks from this, divide by 512.

Returns

On success, the raw size of the SD card in bytes. On error, (uint64)-1.

Error Conditions:

EIO - an I/O error occurred in reading data
ENXIO - SD card support was not initialized

sd_init()

int sd_init

(

void

)

Initialize the SD card for use.

This function initializes the SD card for first use. This includes all steps of the basic initialization sequence for SPI mode, as documented in the SD card spec and at http://elm-chan.org/docs/mmc/mmc_e.html . This also will call scif_sd_init() for you, so you don't have to worry about that ahead of time.

Return values

0	On success.
-1	On failure. This could indicate any number of problems, but probably means that no SD card was detected.

sd_read_blocks()

int sd_read_blocks	(	uint32	block,
		size_t	count,
		uint8 *	buf
	)

Read one or more blocks from the SD card.

This function reads the specified number of blocks from the SD card from the beginning block specified into the buffer passed in. It is your responsibility to allocate the buffer properly for the number of bytes that is to be read (512 * the number of blocks requested).

Parameters

block	The starting block number to read from.
count	The number of 512 byte blocks of data to read.
buf	The buffer to read into.

Return values

0	On success.
-1	On error, errno will be set as appropriate.

Error Conditions:

EIO - an I/O error occurred in reading data
ENXIO - SD card support was not initialized

sd_shutdown()

int sd_shutdown

(

void

)

Shut down SD card support.

This function shuts down SD card support, and cleans up anything that the sd_init() function set up.

Return values

0	On success.
-1	On failure. The only currently defined error is if the card was never initialized to start with.

sd_write_blocks()

int sd_write_blocks	(	uint32	block,
		size_t	count,
		const uint8 *	buf
	)

Write one or more blocks to the SD card.

This function writes the specified number of blocks to the SD card at the beginning block specified from the buffer passed in. Each block is 512 bytes in length, and you must write at least one block at a time. You cannot write partial blocks.

If this function returns an error, you have quite possibly corrupted something on the card or have a damaged card in general (unless errno is ENXIO).

Parameters

block	The starting block number to write to.
count	The number of 512 byte blocks of data to write.
buf	The buffer to write from.

Return values

0	On success.
-1	On error, errno will be set as appropriate.

Error Conditions:

EIO - an I/O error occurred in reading data
ENXIO - SD card support was not initialized