path: root/share/man/man4/iic.4

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.\" Copyright (c) 1998, Nicolas Souchu
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.Dd May 15, 2015
.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
(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.
.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.
.Dv I2CSTART
must have previously been issued on the same file descriptor.
.It Dv I2CSTOP
No argument is passed.
Sends the stop condition to the bus.
If
.Dv 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.
.It Dv I2CRSTCARD
.Pq Vt "struct iiccmd"
Resets the bus.
The argument is completely ignored.
This command does not require
.Dv I2CSTART
to have been previously issued on the file descriptor.
If it was previously issued, exclusive ownership of the underlying iicbus
instance is released.
.It Dv I2CWRITE
.Pq Vt "struct iiccmd"
Writes data to the
.Xr iicbus 4 .
The bus must already be started by a previous
.Dv I2CSTART
on the file descriptor.
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 must already be started by a previous
.Dv I2CSTART
on the file descriptor.
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.
Any previous transaction started by
.Dv I2CSTART
must be terminated by
.Dv I2CSTOP
or
.Dv I2CRSTCARD
before
.Dv I2CRDWR
can be issued on the same file descriptor.
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.
.It Dv I2CSADDR
.Pq Vt "uint8_t"
Associate the specified address with the file descriptor for use by
subsequent
.Xr read 2
or
.Xr 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.
.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_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;
};
.Ed
.Pp
It is also possible to use
.Xr read 2
or
.Xr write 2 ,
in which case the I2C start/stop handshake is managed by
.Xr iicbus 4 .
The address used for the read/write operation is the one passed to the most
recent
.Dv I2CSTART
.Xr ioctl 2
or
.Dv I2CSADDR
.Xr ioctl 2
on the open
.Pa /dev/iic?
file descriptor.
Closing the file descriptor clears any addressing state established by a
previous
.Dv I2CSTART
or
.Dv I2CSADDR ,
stops any transaction established by a not-yet-terminated
.Dv 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
.Pa /dev/iic?
device.
Concurrent transactions on those descriptors are synchronized by the
exclusive-ownership requests issued to the underlying iicbus instance.
.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 .