diff options
Diffstat (limited to 'Documentation/i2c/smbus-protocol.rst')
| -rw-r--r-- | Documentation/i2c/smbus-protocol.rst | 107 |
1 files changed, 64 insertions, 43 deletions
diff --git a/Documentation/i2c/smbus-protocol.rst b/Documentation/i2c/smbus-protocol.rst index e30eb1d274c6..c122ed239f7f 100644 --- a/Documentation/i2c/smbus-protocol.rst +++ b/Documentation/i2c/smbus-protocol.rst @@ -1,6 +1,6 @@ -====================== -SMBus Protocol Summary -====================== +================== +The SMBus Protocol +================== The following is a summary of the SMBus protocol. It applies to all revisions of the protocol (1.0, 1.1, and 2.0). @@ -27,27 +27,27 @@ a different protocol operation entirely. Each transaction type corresponds to a functionality flag. Before calling a transaction function, a device driver should always check (just once) for the corresponding functionality flag to ensure that the underlying I2C -adapter supports the transaction in question. See -<file:Documentation/i2c/functionality.rst> for the details. +adapter supports the transaction in question. See :doc:`functionality` for +the details. 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 +S Start condition +P Stop condition +Rd/Wr (1 bit) Read/Write bit. Rd equals 1, Wr equals 0. +A, NA (1 bit) Acknowledge (ACK) and Not Acknowledge (NACK) 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 +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 +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. +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 +[..] Data sent by I2C device, as opposed to data sent by the host adapter. =============== ============================================================= @@ -62,8 +62,10 @@ This sends a single bit to the device, at the place of the Rd/Wr bit:: Functionality flag: I2C_FUNC_SMBUS_QUICK -SMBus Receive Byte: i2c_smbus_read_byte() -========================================== +SMBus Receive Byte +================== + +Implemented by i2c_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 @@ -75,8 +77,10 @@ the previous SMBus command:: Functionality flag: I2C_FUNC_SMBUS_READ_BYTE -SMBus Send Byte: i2c_smbus_write_byte() -======================================== +SMBus Send Byte +=============== + +Implemented by i2c_smbus_write_byte() This operation is the reverse of Receive Byte: it sends a single byte to a device. See Receive Byte for more information. @@ -88,8 +92,10 @@ to a device. See Receive Byte for more information. Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE -SMBus Read Byte: i2c_smbus_read_byte_data() -============================================ +SMBus Read Byte +=============== + +Implemented by i2c_smbus_read_byte_data() This reads a single byte from a device, from a designated register. The register is specified through the Comm byte:: @@ -99,8 +105,10 @@ The register is specified through the Comm byte:: Functionality flag: I2C_FUNC_SMBUS_READ_BYTE_DATA -SMBus Read Word: i2c_smbus_read_word_data() -============================================ +SMBus Read Word +=============== + +Implemented by i2c_smbus_read_word_data() This operation is very like Read Byte; again, data is read from a device, from a designated register that is specified through the Comm @@ -110,13 +118,15 @@ byte. But this time, the data is a complete word (16 bits):: Functionality flag: I2C_FUNC_SMBUS_READ_WORD_DATA -Note the convenience function i2c_smbus_read_word_swapped is +Note the convenience function i2c_smbus_read_word_swapped() is available for reads where the two data bytes are the other way around (not SMBus compliant, but very popular.) -SMBus Write Byte: i2c_smbus_write_byte_data() -============================================== +SMBus Write Byte +================ + +Implemented by i2c_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 @@ -129,24 +139,26 @@ the Read Byte operation. Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE_DATA -SMBus Write Word: i2c_smbus_write_word_data() -============================================== +SMBus Write Word +================ + +Implemented by i2c_smbus_write_word_data() This is the opposite of the Read Word operation. 16 bits -of data is written to a device, to the designated register that is -specified through the Comm byte.:: +of data are written to a device, to the designated register that is +specified through the Comm byte:: S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P Functionality flag: I2C_FUNC_SMBUS_WRITE_WORD_DATA -Note the convenience function i2c_smbus_write_word_swapped is +Note the convenience function i2c_smbus_write_word_swapped() is available for writes where the two data bytes are the other way around (not SMBus compliant, but very popular.) -SMBus Process Call: -=================== +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:: @@ -157,8 +169,10 @@ This command selects a device register (through the Comm byte), sends Functionality flag: I2C_FUNC_SMBUS_PROC_CALL -SMBus Block Read: i2c_smbus_read_block_data() -============================================== +SMBus Block Read +================ + +Implemented by i2c_smbus_read_block_data() 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 @@ -172,8 +186,10 @@ of data is specified by the device in the Count byte. Functionality flag: I2C_FUNC_SMBUS_READ_BLOCK_DATA -SMBus Block Write: i2c_smbus_write_block_data() -================================================ +SMBus Block Write +================= + +Implemented by i2c_smbus_write_block_data() 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 @@ -266,16 +282,19 @@ This is implemented the following way in the Linux kernel: I2C Block Transactions ====================== -The following I2C block transactions are supported by the -SMBus layer and are described here for completeness. -They are *NOT* defined by the SMBus specification. +The following I2C block transactions are similar to the SMBus Block Read +and Write operations, except these do not have a Count byte. They are +supported by the SMBus layer and are described here for completeness, but +they are *NOT* defined by the SMBus specification. I2C block transactions do not limit the number of bytes transferred but the SMBus layer places a limit of 32 bytes. -I2C Block Read: i2c_smbus_read_i2c_block_data() -================================================ +I2C Block Read +============== + +Implemented by i2c_smbus_read_i2c_block_data() This command reads a block of bytes from a device, from a designated register that is specified through the Comm byte:: @@ -286,8 +305,10 @@ designated register that is specified through the Comm byte:: Functionality flag: I2C_FUNC_SMBUS_READ_I2C_BLOCK -I2C Block Write: i2c_smbus_write_i2c_block_data() -================================================== +I2C Block Write +=============== + +Implemented by i2c_smbus_write_i2c_block_data() The opposite of the Block Read command, this writes bytes to a device, to a designated register that is specified through the |