typedef struct {
// Initialization status. 0 == not woken 8 == woken 9 == CMD0 received
// 10 == CMD8 received, 11 == CMD55 received, 12 == CMD41 received (fully
// initialized).
unsigned int initstat;
// We receive commands into this buffer.
byte recvbuf[6];
// Where the next SPI byte should be stored in recvbuf.
unsigned int recvidx;
// Buffer to the arguments for a response
byte sendbuf[5];
// Index of the next byte from sendbuf we should return. If -1, buffer is
// empty.
int sendidx;
// File used for contents read/write
FILE *fp;
// number of bytes read into the current CMD17. -1 means no CMD17 active.
int cmd17bytes;
// number of bytes received for the current CMD24. -2 means no CMD24 active.
// -1 means we're still waiting for the data token.
int cmd24bytes;
// running crc16 during read and write operations.
uint16_t crc16;
} SDC;
