mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-15 10:36:55 +07:00
1da177e4c3
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!
217 lines
6.4 KiB
Plaintext
217 lines
6.4 KiB
Plaintext
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
|
|
|
|
|