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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 is non-zero when additional write commands will follow. 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 write. The last element is a
boolean flag. It is non-zero when additional write commands will follow. 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.