MultiMediaCard Protocol - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 119

fies the sector to read (sector_addr) and a pointer to a buffer that will store
the data read from the card (buffer). The function returns a status code.
// This macro writes FFh twice to clock in two CRC bytes.

#define mReadCRC() WriteSPI(0xFF); WriteSPI(0xFF);

#define SDC_FLOATING_BUS 0xFF
#define SDC_BAD_RESPONSE SDC_FLOATING_BUS
#define SDC_SECTOR_SIZE 512

SDC_Error SectorRead(dword sector_addr, byte* buffer)
{
byte data_token;

word index;

SDC_RESPONSE response;

SDC_Error status = sdcValid;

// Issue a READ_SINGLE_BLOCK command.
// Specify the address of the first byte to read in the media.
// To obtain the address of a sector's first byte,
// shift the sector address left 9 times to multiply by 512 (sector size).

response = SendSDCCmd(READ_SINGLE_BLOCK, (sector_addr << 9));

// A response of 00h indicates success.

if (response.r1._byte != 0x00)
{
status = sdcCardBadCmd;
}
else
{
// The command was accepted.

index = 0x2FF;