SMBus Protocol Summary======================The following is a summary of the SMBus protocol. It applies toall revisions of the protocol (1.0, 1.1, and 2.0).Certain protocol features which are not supported bythis package are briefly described at the end of this document.Some adapters understand only the SMBus (System Management Bus) protocol,which is a subset from the I2C protocol. Fortunately, many devices useonly the same subset, which makes it possible to put them on an SMBus.If you write a driver for some I2C device, please try to use the SMBuscommands if at all possible (if the device uses only that subset of theI2C protocol). This makes it possible to use the device driver on bothSMBus adapters and I2C adapters (the SMBus command set is automaticallytranslated to I2C on I2C adapters, but plain I2C commands can not behandled at all on most pure SMBus adapters).Below is a list of SMBus commands.Key to symbols==============S     (1 bit) : Start bitP     (1 bit) : Stop bitRd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0.A, NA (1 bit) : Accept and reverse accept bit. Addr  (7 bits): I2C 7 bit address. Note that this can be expanded as usual to                 get a 10 bit I2C address.Comm  (8 bits): Command byte, a data byte which often selects a register on                the device.Data  (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh                for 16 bit data.Count (8 bits): A data byte containing the length of a block operation.[..]: Data sent by I2C device, as opposed to data sent by the host adapter.SMBus Write Quick=================This sends a single bit to the device, at the place of the Rd/Wr bit.There is no equivalent Read Quick command.A Addr Rd/Wr [A] PSMBus Read Byte===============This reads a single byte from a device, without specifying a deviceregister. Some devices are so simple that this interface is enough; forothers, it is a shorthand if you want to read the same register as inthe previous SMBus command.S Addr Rd [A] [Data] NA PSMBus Write Byte================This is the reverse of Read Byte: it sends a single byte to a device.See Read Byte for more information.S Addr Wr [A] Data [A] PSMBus Read Byte Data====================This reads a single byte from a device, from a designated register.The register is specified through the Comm byte.S Addr Wr [A] Comm [A] S Addr Rd [A] [Data] NA PSMBus Read Word Data====================This command is very like Read Byte Data; again, data is read from adevice, from a designated register that is specified through the Commbyte. But this time, the data is a complete word (16 bits).S Addr Wr [A] Comm [A] S Addr Rd [A] [DataLow] A [DataHigh] NA PSMBus Write Byte Data=====================This writes a single byte to a device, to a designated register. Theregister is specified through the Comm byte. This is the opposite ofthe Read Byte Data command.S Addr Wr [A] Comm [A] Data [A] PSMBus Write Word Data=====================This is the opposite operation of the Read Word Data command. 16 bitsof data is read from a device, from a designated register that is specified through the Comm byte. S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] PSMBus Process Call==================This command selects a device register (through the Comm byte), sends16 bits of data to it, and reads 16 bits of data in return.S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A]                              S Addr Rd [A] [DataLow] A [DataHigh] NA PSMBus Block Read================This command reads a block of up to 32 bytes from a device, from a designated register that is specified through the Comm byte. The amountof data is specified by the device in the Count byte.S Addr Wr [A] Comm [A]            S Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA PSMBus Block Write=================The opposite of the Block Read command, this writes up to 32 bytes to a device, to a designated register that is specified through theComm byte. The amount of data is specified in the Count byte.S Addr Wr [A] Comm [A] Count [A] Data [A] Data [A] ... [A] Data [A] PSMBus Block Process Call========================SMBus Block Process Call was introduced in Revision 2.0 of the specification.This command selects a device register (through the Comm byte), sends1 to 31 bytes of data to it, and reads 1 to 31 bytes of data in return.S Addr Wr [A] Comm [A] Count [A] Data [A] ...                             S Addr Rd [A] [Count] A [Data] ... A PSMBus Host Notify=================This command is sent from a SMBus device acting as a master to theSMBus host acting as a slave.It is the same form as Write Word, with the command code replaced by thealerting device's address.[S] [HostAddr] [Wr] A [DevAddr] A [DataLow] A [DataHigh] A [P]Packet Error Checking (PEC)===========================Packet Error Checking was introduced in Revision 1.1 of the specification.PEC adds a CRC-8 error-checking byte to all transfers.Address Resolution Protocol (ARP)=================================The Address Resolution Protocol was introduced in Revision 2.0 ofthe specification. It is a higher-layer protocol which uses themessages above.ARP adds device enumeration and dynamic address assignment tothe protocol. All ARP communications use slave address 0x61 andrequire PEC checksums.I2C Block Transactions======================The following I2C block transactions are supported by theSMBus layer and are described here for completeness.I2C block transactions do not limit the number of bytes transferredbut the SMBus layer places a limit of 32 bytes.I2C Block Read==============This command reads a block of bytes from a device, from a designated register that is specified through the Comm byte.S Addr Wr [A] Comm [A]            S Addr Rd [A] [Data] A [Data] A ... A [Data] NA PI2C Block Read (2 Comm bytes)=============================This command reads a block of bytes from a device, from a designated register that is specified through the two Comm bytes.S Addr Wr [A] Comm1 [A] Comm2 [A]            S Addr Rd [A] [Data] A [Data] A ... A [Data] NA PI2C Block Write===============The opposite of the Block Read command, this writes bytes to a device, to a designated register that is specified through theComm byte. Note that command lengths of 0, 2, or more bytes aresupported as they are indistinguishable from data.S Addr Wr [A] Comm [A] Data [A] Data [A] ... [A] Data [A] P