iicbus(4) [debian man page]
IICBUS(4) BSD Kernel Interfaces Manual IICBUS(4) NAME
iicbus -- I2C bus system SYNOPSIS
device iicbus device iicbb device iic device ic device iicsmb DESCRIPTION
The iicbus system provides a uniform, modular and architecture-independent system for the implementation of drivers to control various I2C devices and to utilize different I2C controllers. I2C I2C is an acronym for Inter Integrated Circuit bus. The I2C bus was developed in the early 1980's by Philips semiconductors. Its purpose was to provide an easy way to connect a CPU to peripheral chips in a TV-set. The BUS physically consists of 2 active wires and a ground connection. The active wires, SDA and SCL, are both bidirectional. Where SDA is the Serial DAta line and SCL is the Serial CLock line. Every component hooked up to the bus has its own unique address whether it is a CPU, LCD driver, memory, or complex function chip. Each of these chips can act as a receiver and/or transmitter depending on its functionality. Obviously an LCD driver is only a receiver, while a memory or I/O chip can both be transmitter and receiver. Furthermore there may be one or more BUS MASTERs. The BUS MASTER is the chip issuing the commands on the BUS. In the I2C protocol specification it is stated that the IC that initiates a data transfer on the bus is considered the BUS MASTER. At that time all the others are regarded to as the BUS SLAVEs. As mentioned before, the IC bus is a Multi-MASTER BUS. This means that more than one IC capable of initiating data transfer can be connected to it. DEVICES
Some I2C device drivers are available: Devices Description iic general i/o operation ic network IP interface iicsmb I2C to SMB software bridge INTERFACES
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 capabili- ties of the I2C protocol. Some I2C interfaces are available: Interface Description 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 SEE ALSO
iicbb(4), lpbb(4), pcf(4) HISTORY
The iicbus manual page first appeared in FreeBSD 3.0. AUTHORS
This manual page was written by Nicolas Souchu. BSD
August 6, 1998 BSD
Check Out this Related Man Page
IIC(4) BSD Kernel Interfaces Manual IIC(4) NAME
iic -- I2C generic I/O device driver SYNOPSIS
device iic #include <dev/iicbus/iic.h> DESCRIPTION
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. All other elements are ignored. I2CRPTSTART (struct iiccmd) Sends the repeated start condition to the slave specified by the slave element to the bus. All other elements are ignored. I2CSTOP No argument is passed. Sends the stop condition to the bus. This terminates the current transaction. I2CRSTCARD (struct iiccmd) Resets the bus. The argument is completely ignored. I2CWRITE (struct iiccmd) Writes data to the iicbus(4). The bus should already be started. The slave element is ignored. The count ele- ment is the number of bytes to write. The last element is a boolean flag. It is non-zero when additional write commands will follow. 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 should already be started. The slave element is ignored. The count element is the number of bytes to write. The last element is a boolean flag. It is non-zero when additional write commands will follow. The buf element is a pointer to where to store the data read from the bus. Short reads on the bus produce unde- fined results. I2CRDWR (struct iic_rdwr_data) Generic read/write interface. Allows for an arbitrary number of commands to be sent to an arbitrary num- ber of devices on the bus. A read transfer is specified if IIC_M_RD is set in flags. Otherwise the transfer is a write trans- fer. The slave element specifies the 7-bit address for the transfer. The len element is the length of the data. The buf ele- ment is a buffer for that data. This ioctl is intended to be Linux compatible. 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_RD 0x0001 /* read vs write */ uint16_t len; /* msg legnth */ uint8_t * buf; }; struct iic_rdwr_data { struct iic_msg *msgs; uint32_t nmsgs; }; It is also possible to use read/write routines, then I2C start/stop handshake is managed by the iicbus(4) system. However, the address used for the read/write routines is the one passed to last I2CSTART ioctl(2) to this device. SEE ALSO
ioctl(2), read(2), write(2), iicbus(4) HISTORY
The iic manual page first appeared in FreeBSD 3.0. AUTHORS
This manual page was written by Nicolas Souchu and M. Warner Losh. BUGS
Only the I2CRDWR ioctl(2) is thread safe. All other interfaces suffer from some kind of race. BSD
September 6, 2006 BSD