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+This document describes the i2c protocol. Or will, when it is finished :-)
+
+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.
+
+
+Simple send transaction
+======================
+
+This corresponds to i2c_master_send.
+
+ S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P
+
+
+Simple receive transaction
+===========================
+
+This corresponds to i2c_master_recv
+
+ S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
+
+
+Combined transactions
+====================
+
+This corresponds to i2c_transfer
+
+They are just like the above transactions, but instead of a stop bit P
+a start bit S is sent and the transaction continues. An example of
+a byte read, followed by a byte write:
+
+ S Addr Rd [A] [Data] NA S Addr Wr [A] Data [A] P
+
+
+Modified transactions
+=====================
+
+The following modifications to the I2C protocol can also be generated,
+with the exception of I2C_M_NOSTART these are usually only needed to
+work around device issues:
+
+ Flag I2C_M_NOSTART:
+ In a combined transaction, no 'S Addr Wr/Rd [A]' is generated at some
+ point. For example, setting I2C_M_NOSTART on the second partial message
+ generates something like:
+ S Addr Rd [A] [Data] NA Data [A] P
+ If you set the I2C_M_NOSTART variable for the first partial message,
+ we do not generate Addr, but we do generate the startbit S. This will
+ probably confuse all other clients on your bus, so don't try this.
+
+ This is often used to gather transmits from multiple data buffers in
+ system memory into something that appears as a single transfer to the
+ I2C device but may also be used between direction changes by some
+ rare devices.
+
+ Flags I2C_M_REV_DIR_ADDR
+ This toggles the Rd/Wr flag. That is, if you want to do a write, but
+ need to emit an Rd instead of a Wr, or vice versa, you set this
+ flag. For example:
+ S Addr Rd [A] Data [A] Data [A] ... [A] Data [A] P
+
+ Flags I2C_M_IGNORE_NAK
+ Normally message is interrupted immediately if there is [NA] from the
+ client. Setting this flag treats any [NA] as [A], and all of
+ message is sent.
+ These messages may still fail to SCL lo->hi timeout.
+
+ Flags I2C_M_NO_RD_ACK
+ In a read message, master A/NA bit is skipped.