From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 16 Apr 2005 15:20:36 -0700 Subject: Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip! --- Documentation/i2c/smbus-protocol | 216 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 216 insertions(+) create mode 100644 Documentation/i2c/smbus-protocol (limited to 'Documentation/i2c/smbus-protocol') diff --git a/Documentation/i2c/smbus-protocol b/Documentation/i2c/smbus-protocol new file mode 100644 index 00000000000..09f5e5ca492 --- /dev/null +++ b/Documentation/i2c/smbus-protocol @@ -0,0 +1,216 @@ +SMBus Protocol Summary +====================== +The following is a summary of the SMBus protocol. It applies to +all revisions of the protocol (1.0, 1.1, and 2.0). +Certain protocol features which are not supported by +this 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 use +only 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 SMBus +commands if at all possible (if the device uses only that subset of the +I2C protocol). This makes it possible to use the device driver on both +SMBus adapters and I2C adapters (the SMBus command set is automatically +translated to I2C on I2C adapters, but plain I2C commands can not be +handled at all on most pure SMBus adapters). + +Below is a list of SMBus commands. + +Key to symbols +============== + +S (1 bit) : Start bit +P (1 bit) : Stop bit +Rd/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] P + + +SMBus Read Byte +=============== + +This reads a single byte from a device, without specifying a device +register. Some devices are so simple that this interface is enough; for +others, it is a shorthand if you want to read the same register as in +the previous SMBus command. + +S Addr Rd [A] [Data] NA P + + +SMBus 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] P + + +SMBus 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 P + + +SMBus Read Word Data +==================== + +This command is very like Read Byte Data; again, data is read from a +device, from a designated register that is specified through the Comm +byte. 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 P + + +SMBus Write Byte Data +===================== + +This writes a single byte to a device, to a designated register. The +register is specified through the Comm byte. This is the opposite of +the Read Byte Data command. + +S Addr Wr [A] Comm [A] Data [A] P + + +SMBus Write Word Data +===================== + +This is the opposite operation of the Read Word Data command. 16 bits +of 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] P + + +SMBus Process Call +================== + +This command selects a device register (through the Comm byte), sends +16 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 P + + +SMBus 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 amount +of 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 P + + +SMBus 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 the +Comm 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] P + + +SMBus 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), sends +1 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 P + + +SMBus Host Notify +================= + +This command is sent from a SMBus device acting as a master to the +SMBus host acting as a slave. +It is the same form as Write Word, with the command code replaced by the +alerting 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 of +the specification. It is a higher-layer protocol which uses the +messages above. + +ARP adds device enumeration and dynamic address assignment to +the protocol. All ARP communications use slave address 0x61 and +require PEC checksums. + + +I2C Block Transactions +====================== +The following I2C block transactions are supported by the +SMBus layer and are described here for completeness. +I2C block transactions do not limit the number of bytes transferred +but 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 P + + +I2C 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 P + + +I2C Block Write +=============== + +The opposite of the Block Read command, this writes bytes to +a device, to a designated register that is specified through the +Comm byte. Note that command lengths of 0, 2, or more bytes are +supported as they are indistinguishable from data. + +S Addr Wr [A] Comm [A] Data [A] Data [A] ... [A] Data [A] P + + -- cgit v1.2.3