.\" Copyright (c) 2006, M. Warner Losh
.\" Copyright (c) 1998, Nicolas Souchu
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.Dd June 24, 2014
.Dt IIC 4
.Os
.Sh NAME
.Nm iic
.Nd I2C generic I/O device driver
.Sh SYNOPSIS
.Cd "device iic"
.Pp
.In dev/iicbus/iic.h
.Sh DESCRIPTION
The
.Nm
device driver provides generic I/O to any
.Xr iicbus 4
instance.
In order to control I2C devices, use
.Pa /dev/iic?
with the
following ioctls:
.Bl -tag -width ".Dv I2CRPTSTART"
.It Dv I2CSTART
.Pq Vt "struct iiccmd"
Sends the start condition to the slave specified by the
.Va slave
element to the bus.
The
.Va slave
element consists of a 7-bit address and a read/write bit
(i.e., 7-bit address << 1 | r/w).
If the read/write bit is set a read operation is initiated, if the read/write
bit is cleared a write operation is initiated.
All other elements are ignored.
.It Dv I2CRPTSTART
.Pq Vt "struct iiccmd"
Sends the repeated start condition to the slave specified by the
.Va slave
element to the bus.
The slave address should be specified as in
.Dv I2CSTART .
All other elements are ignored.
.It Dv I2CSTOP
No argument is passed.
Sends the stop condition to the bus.
This terminates the current transaction.
.It Dv I2CRSTCARD
.Pq Vt "struct iiccmd"
Resets the bus.
The argument is completely ignored.
.It Dv I2CWRITE
.Pq Vt "struct iiccmd"
Writes data to the
.Xr iicbus 4 .
The bus should already be started.
The
.Va slave
element is ignored.
The
.Va count
element is the number of bytes to write.
The
.Va last
element is a boolean flag.
It is non-zero when additional write commands will follow.
The
.Va buf
element is a pointer to the data to write to the bus.
.It Dv I2CREAD
.Pq Vt "struct iiccmd"
Reads data from the
.Xr iicbus 4 .
The bus should already be started.
The
.Va slave
element is ignored.
The
.Va count
element is the number of bytes to write.
The
.Va last
element is a boolean flag.
It is non-zero when additional write commands will follow.
The
.Va buf
element is a pointer to where to store the data read from the bus.
Short reads on the bus produce undefined results.
.It Dv I2CRDWR
.Pq Vt "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.
A read transfer is specified if
.Dv IIC_M_RD
is set in
.Va flags .
Otherwise the transfer is a write transfer.
The
.Va 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
.Va len
element is the number of
.Pq Vt "struct iic_msg"
messages encoded on
.Pq Vt "struct iic_rdwr_data" .
The
.Va buf
element is a buffer for that data.
This ioctl is intended to be
.Tn Linux
compatible.
.El
.Pp
The following data structures are defined in
.In dev/iicbus/iic.h
and referenced above:
.Bd -literal -offset indent
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_RD	0x0001	/* read vs write */
	uint16_t	len;	/* msg length */
	uint8_t *	buf;
};

struct iic_rdwr_data {
	struct iic_msg *msgs;
	uint32_t nmsgs;
};
.Ed
.Pp
It is also possible to use read/write routines, then I2C start/stop handshake is
managed by the
.Xr iicbus 4
system.
However, the address used for the read/write routines is the one
passed to last
.Dv I2CSTART
.Xr ioctl 2
to this device.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr read 2 ,
.Xr write 2 ,
.Xr iicbus 4
.Sh HISTORY
The
.Nm
manual page first appeared in
.Fx 3.0 .
.Sh AUTHORS
.An -nosplit
This
manual page was written by
.An Nicolas Souchu
and
.An M. Warner Losh .
.Sh BUGS
Only the
.Dv I2CRDWR
.Xr ioctl 2
is thread safe.
All other interfaces suffer from some kind of race.