Linux Kernel 设备驱动之I2C之client之发送消息格式

 * struct i2c_msg - an I2C transaction segment beginning with START
 * @addr: Slave address, either seven or ten bits.  When this is a ten
 * bit address, I2C_M_TEN must be set in @flags and the adapter
 * must support I2C_FUNC_10BIT_ADDR.
 * @flags: I2C_M_RD is handled by all adapters.  No other flags may be
 * provided unless the adapter exported the relevant I2C_FUNC_*
 * flags through i2c_check_functionality().
 * @len: Number of data bytes in @buf being read from or written to the
 * I2C slave address.  For read transactions where I2C_M_RECV_LEN
 * is set, the caller guarantees that this buffer can hold up to
 * 32 bytes in addition to the initial length byte sent by the
 * slave (plus, if used, the SMBus PEC); and this value will be
 * incremented by the number of block data bytes received.
 * @buf: The buffer into which data is read, or from which it's written.
 * An i2c_msg is the low level representation of one segment of an I2C
 * transaction.  It is visible to drivers in the @i2c_transfer() procedure,
 * to userspace from i2c-dev, and to I2C adapter drivers through the
 * @[email protected]_xfer() method.
 * Except when I2C "protocol mangling" is used, all I2C adapters implement
 * the standard rules for I2C transactions.  Each transaction begins with a
 * START.  That is followed by the slave address, and a bit encoding read
 * versus write.  Then follow all the data bytes, possibly including a byte
 * with SMBus PEC.  The transfer terminates with a NAK, or when all those
 * bytes have been transferred and ACKed.  If this is the last message in a
 * group, it is followed by a STOP.  Otherwise it is followed by the next
 * @i2c_msg transaction segment, beginning with a (repeated) START.
 * Alternatively, when the adapter supports I2C_FUNC_PROTOCOL_MANGLING then
 * passing certain @flags may have changed those standard protocol behaviors.
 * Those flags are only for use with broken/nonconforming slaves, and with
 * adapters which are known to support the specific mangling options they
 * need (one or more of IGNORE_NAK, NO_RD_ACK, NOSTART, and REV_DIR_ADDR).
struct i2c_msg {
 __u16 addr; /* slave address   */
 __u16 flags;
#define I2C_M_RD  0x0001 /* read data, from slave to master */
     /* I2C_M_RD is guaranteed to be 0x0001! */
#define I2C_M_TEN  0x0010 /* this is a ten bit chip address */
#define I2C_M_RECV_LEN  0x0400 /* length will be first received byte */
#define I2C_M_NO_RD_ACK  0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NOSTART  0x4000 /* if I2C_FUNC_NOSTART */
#define I2C_M_STOP  0x8000 /* if I2C_FUNC_PROTOCOL_MANGLING */
 __u16 len;  /* msg length    */
 __u8 *buf;  /* pointer to msg data   */
 * Data for SMBus Messages
#define I2C_SMBUS_BLOCK_MAX 32 /* As specified in SMBus standard */
union i2c_smbus_data {
 __u8 byte;
 __u16 word;
 __u8 block[I2C_SMBUS_BLOCK_MAX + 2]; /* block[0] is used for length */
          /* and one more for user-space compatibility */