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Mostly re-write man page to reflect current state of this interface.

Warn of races.

# Doc police: Please review
This commit is contained in:
Warner Losh 2006-09-06 21:43:55 +00:00
parent ccf118a50a
commit 723e155201
Notes: svn2git 2020-12-20 02:59:44 +00:00
svn path=/head/; revision=162082

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@ -1,3 +1,4 @@
.\" Copyright (c) 2006, M. Warner Losh
.\" Copyright (c) 1998, Nicolas Souchu
.\" All rights reserved.
.\"
@ -24,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd October 25, 1998
.Dd September 6, 2006
.Dt IIC 4
.Os
.Sh NAME
@ -32,6 +33,8 @@
.Nd I2C generic i/o device driver
.Sh SYNOPSIS
.Cd "device iic"
.Pp
.In dev/iicbus/iic.h
.Sh DESCRIPTION
The
.Em iic
@ -43,16 +46,113 @@ In order to control I2C devices, use
with the
following ioctls:
.Pp
.Bl -column "I2CRSTCARD" -compact
.It Em Ioctl Ta Em Description
.It Sy I2CSTART Ta "send start condition to the specified device (with 7-bit address) on the bus"
.It Sy I2CSTOP Ta "send stop condition to the bus"
.It Sy I2CRSTCARD Ta "reset the bus"
.Bl -tag -wdith ".Dv I2CRSTCARD"
.It Dv I2CSTART
.Vt "struct iiccmd" ;
Sends the start condition to the slave specified by the
.Vt slave
element to the bus.
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
.Vt "struct iiccmd" ;
Resets the bus.
The argument is completely ignored.
.It Dv I2CWRITE
.Vt "struct iiccmd" ;
Writes data to the iicbus.
The bus should already be started.
.Vt "slave"
is ignored.
.Vt "count"
is the number of bytes to write.
.Vt "last"
is a boolean flag.
It is non-zero when additional write commands will follow.
.Vt "buf"
is a pointer to the data to write to the bus.
.It Dv I2CREAD
.Vt "struct iiccmd" ;
Reads data from the iicbus.
The bus should already be started.
.Vt "slave"
is ignored.
.Vt "count"
is the number of bytes to write.
.Vt "last"
is a boolean flag.
It is non-zero when additional write commands will follow.
.Vt "buf"
is a pointer to where to store the data read from the bus.
Short reads on the bus produce undefined results.
.It Dv I2CRDWR
.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 speficied if
.Vt IIC_M_RD
is set in
.Vt flags .
Otherwise the transfer is a write transfer.
The
.Vt slave
specifieds the 7-bit address for the transfer.
.Vt len
is the length of the data.
.Vt buf
is a buffer for that data.
This ioctl is intended to be Linux compatible.
.El
.Pp
The following data structures are defined in
.In dev/iicbus/iic.h
and referenced above:
.Bd -literal
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 legnth */
uint8_t * buf;
};
struct iic_rdwr_data {
struct iic_msg *msgs;
uint32_t nmsgs;
};
.Ed
.Pp
You may also use read/write routines, then I2C start/stop handshake is
managed by the iicbus 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 BUGS
Only the
.Dv I2CRDWR
.Xr ioctl 2
is thread safe.
All other interfaces suffer from some kind of race.
.Sh SEE ALSO
.Xr ioctl 2
.Xr read 2
.Xr write 2
.Xr iicbus 4
.Sh HISTORY
The
@ -62,4 +162,6 @@ manual page first appeared in
.Sh AUTHORS
This
manual page was written by
.An Nicolas Souchu .
.An Nicolas Souchu
and
.An M. Warner Losh .