iic
—
I2C generic I/O device driver
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.
The iic
manual page first appeared in
FreeBSD 3.0.
This manual page was written by Nicolas Souchu and
M. Warner Losh.