| Devices Description
iic general i/o operation
ic network IP interface
iicsmb I2C to SMB software bridge
The I2C protocol may be implemented by hardware or software. Software interfaces rely on very simple hardware, usually two lines twiddled by 2 registers. Hardware interfaces are more intelligent and receive 8-bit characters they write to the bus according to the I2C protocol.
I2C interfaces may act on the bus as slave devices, allowing spontaneous bidirectional communications, thanks to the multi-master capabilities of the I2C protocol.
Some I2C interfaces are available:
pcf Philips PCF8584 master/slave interface
iicbb generic bit-banging master-only driver
lpbb parallel port specific bit-banging interface
bktr Brooktree848 video chipset, hardware and software master-only interface
The operating frequency of an I2C bus may be fixed or configurable. The bus may be used as part of some larger standard interface, and that interface specification may require a fixed frequency. The driver for that hardware would not honor an attempt to configure a different speed. A general purpose I2C bus, such as those found in many embedded systems, will often support multiple bus frequencies.
When a system supports multiple I2C busses, a different frequency can be configured for each bus by number, represented by the %d in the variable names below. Busses can be configured using any combination of device hints, Flattened Device Tree (FDT) data, tunables set via loader(8), or at runtime using sysctl(8). When configuration is supplied using more than one method, FDT and hint data will be overridden by a tunable, which can be overriden by sysctl(8).
Set hint.iicbus.%d.frequency to the frequency in Hz, on systems that use device hints to configure I2C devices. The hint is also honored by systems that use FDT data if no frequency is configured using FDT.
Configure the I2C bus speed using the FDT standard clock-frequency property of the node describing the I2C controller hardware.
Set dev.iicbus.%d.frequency in loader.conf(5). The same variable can be changed at any time with sysctl(8). Reset the bus using i2c(8) or the iic(4) I2CRSTCARD ioctl to make the change take effect.
The iicbus manual page first appeared in
.Fx 3.0 .
This manual page was written by
.An Nicolas Souchu .