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NAME

     iic — I2C generic I/O device driver

SYNOPSIS

     device iic

     #include <dev/iicbus/iic.h>

DESCRIPTION

     The iic device driver provides generic I/O to any iicbus(4) instance.  In order to control
     I2C devices, use /dev/iic? with the following ioctls:

     I2CSTART     (struct iiccmd) Sends the start condition to the slave specified by the slave
                  element to the bus.  The slave element consists of a 7-bit address and a
                  read/write bit (that is, a 7-bit address << 1 | r/w).  A read operation is
                  initiated when the read/write bit is set, or a write operation when it is
                  cleared.  All other elements are ignored.  If successful, the file descriptor
                  receives exclusive ownership of the underlying iicbus instance.

     I2CRPTSTART  (struct iiccmd) Sends the repeated start condition to the slave specified by
                  the slave element to the bus.  The slave address should be specified as in
                  I2CSTART.  All other elements are ignored.  I2CSTART must have previously been
                  issued on the same file descriptor.

     I2CSTOP      No argument is passed.  Sends the stop condition to the bus.  If I2CSTART was
                  previously issued on the file descriptor, the current transaction is terminated
                  and exclusive ownership of the underlying iicbus instance is released.
                  Otherwise, no action is performed.

     I2CRSTCARD   (struct iiccmd) Resets the bus.  The argument is completely ignored.  This
                  command does not require I2CSTART to have been previously issued on the file
                  descriptor.  If it was previously issued, exclusive ownership of the underlying
                  iicbus instance is released.

     I2CWRITE     (struct iiccmd) Writes data to the iicbus(4).  The bus must already be started
                  by a previous I2CSTART on the file descriptor.  The slave element is ignored.
                  The count element is the number of bytes to write.  The last element is a
                  boolean flag.  It must be zero when additional read commands will follow, or
                  non-zero if this is the last command.  The buf element is a pointer to the data
                  to write to the bus.

     I2CREAD      (struct iiccmd) Reads data from the iicbus(4).  The bus must already be started
                  by a previous I2CSTART on the file descriptor.  The slave element is ignored.
                  The count element is the number of bytes to read.  The last element is a
                  boolean flag.  It must be zero when additional read commands will follow, or
                  non-zero if this is the last command.  The buf element is a pointer to where to
                  store the data read from the bus.  Short reads on the bus produce undefined
                  results.

     I2CRDWR      (struct iic_rdwr_data) Generic read/write interface.  Allows for an arbitrary
                  number of commands to be sent to an arbitrary number of devices on the bus.
                  Any previous transaction started by I2CSTART must be terminated by I2CSTOP or
                  I2CRSTCARD before I2CRDWR can be issued on the same file descriptor.  A read
                  transfer is specified if IIC_M_RD is set in flags.  Otherwise the transfer is a
                  write transfer.  The slave element specifies the 7-bit address with the
                  read/write bit for the transfer.  The read/write bit will be handled by the
                  iicbus stack based on the specified transfer operation.  The len element is the
                  number of (struct iic_msg) messages encoded on (struct iic_rdwr_data).  The buf
                  element is a buffer for that data.  This ioctl is intended to be Linux
                  compatible.

     I2CSADDR     (uint8_t) Associate the specified address with the file descriptor for use by
                  subsequent read(2) or write(2) calls.  The argument is an 8-bit address (that
                  is, a 7-bit address << 1).  The read/write bit in the least-significant
                  position is ignored.  Any subsequent read or write operation will set or clear
                  that bit as needed.

     The following data structures are defined in <dev/iicbus/iic.h> and referenced above:

           struct iiccmd {
                   u_char slave;
                   int count;
                   int last;
                   char *buf;
           };

           /* Designed to be compatible with linux's struct i2c_msg */
           struct iic_msg
           {
                   uint16_t        slave;
                   uint16_t        flags;
           #define IIC_M_WR        0       /* Fake flag for write */
           #define IIC_M_RD        0x0001  /* read vs write */
           #define IIC_M_NOSTOP    0x0002  /* do not send a I2C stop after message */
           #define IIC_M_NOSTART   0x0004  /* do not send a I2C start before message */
                   uint16_t        len;    /* msg length */
                   uint8_t *       buf;
           };

           struct iic_rdwr_data {
                   struct iic_msg *msgs;
                   uint32_t nmsgs;
           };

     It is also possible to use read(2) or write(2), in which case the I2C start/stop handshake
     is managed by iicbus(4).  The address used for the read/write operation is the one passed to
     the most recent I2CSTART ioctl(2) or I2CSADDR ioctl(2) on the open /dev/iic? file
     descriptor.  Closing the file descriptor clears any addressing state established by a
     previous I2CSTART or I2CSADDR, stops any transaction established by a not-yet-terminated
     I2CSTART, and releases iicbus ownership.  Because addressing state is stored on a per-file-
     descriptor basis, it is permissible for multiple file descriptors to be simultaneously open
     on the same /dev/iic? device.  Concurrent transactions on those descriptors are synchronized
     by the exclusive-ownership requests issued to the underlying iicbus instance.

SEE ALSO

     ioctl(2), read(2), write(2), iicbus(4)

HISTORY

     The iic manual page first appeared in FreeBSD 3.0.

AUTHORS

     This manual page was written by Nicolas Souchu and M. Warner Losh.