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Linux/Documentation/i2c/i2c-protocol.rst

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Diff markup

Differences between /Documentation/i2c/i2c-protocol.rst (Version linux-6.12-rc7) and /Documentation/i2c/i2c-protocol.rst (Version linux-5.18.19)


  1 ================                                    1 ================
  2 The I2C Protocol                                    2 The I2C Protocol
  3 ================                                    3 ================
  4                                                     4 
  5 This document is an overview of the basic I2C  !!   5 This document describes the I2C protocol. Or will, when it is finished :-)
  6 APIs to perform them.                          << 
  7                                                     6 
  8 Key to symbols                                      7 Key to symbols
  9 ==============                                      8 ==============
 10                                                     9 
 11 =============== ==============================     10 =============== =============================================================
 12 S               Start condition                    11 S               Start condition
 13 P               Stop condition                     12 P               Stop condition
 14 Rd/Wr (1 bit)   Read/Write bit. Rd equals 1, W     13 Rd/Wr (1 bit)   Read/Write bit. Rd equals 1, Wr equals 0.
 15 A, NA (1 bit)   Acknowledge (ACK) and Not Ackn     14 A, NA (1 bit)   Acknowledge (ACK) and Not Acknowledge (NACK) bit
 16 Addr  (7 bits)  I2C 7 bit address. Note that t !!  15 Addr  (7 bits)  I2C 7 bit address. Note that this can be expanded as usual to
 17                 get a 10 bit I2C address.          16                 get a 10 bit I2C address.
 18 Data  (8 bits)  A plain data byte.             !!  17 Comm  (8 bits)  Command byte, a data byte which often selects a register on
                                                   >>  18                 the device.
                                                   >>  19 Data  (8 bits)  A plain data byte. Sometimes, I write DataLow, DataHigh
                                                   >>  20                 for 16 bit data.
                                                   >>  21 Count (8 bits)  A data byte containing the length of a block operation.
 19                                                    22 
 20 [..]            Data sent by I2C device, as op     23 [..]            Data sent by I2C device, as opposed to data sent by the
 21                 host adapter.                      24                 host adapter.
 22 =============== ==============================     25 =============== =============================================================
 23                                                    26 
 24                                                    27 
 25 Simple send transaction                            28 Simple send transaction
 26 =======================                            29 =======================
 27                                                    30 
 28 Implemented by i2c_master_send()::                 31 Implemented by i2c_master_send()::
 29                                                    32 
 30   S Addr Wr [A] Data [A] Data [A] ... [A] Data     33   S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P
 31                                                    34 
 32                                                    35 
 33 Simple receive transaction                         36 Simple receive transaction
 34 ==========================                         37 ==========================
 35                                                    38 
 36 Implemented by i2c_master_recv()::                 39 Implemented by i2c_master_recv()::
 37                                                    40 
 38   S Addr Rd [A] [Data] A [Data] A ... A [Data]     41   S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
 39                                                    42 
 40                                                    43 
 41 Combined transactions                              44 Combined transactions
 42 =====================                              45 =====================
 43                                                    46 
 44 Implemented by i2c_transfer().                     47 Implemented by i2c_transfer().
 45                                                    48 
 46 They are just like the above transactions, but     49 They are just like the above transactions, but instead of a stop
 47 condition P a start condition S is sent and th     50 condition P a start condition S is sent and the transaction continues.
 48 An example of a byte read, followed by a byte      51 An example of a byte read, followed by a byte write::
 49                                                    52 
 50   S Addr Rd [A] [Data] NA S Addr Wr [A] Data [     53   S Addr Rd [A] [Data] NA S Addr Wr [A] Data [A] P
 51                                                    54 
 52                                                    55 
 53 Modified transactions                              56 Modified transactions
 54 =====================                              57 =====================
 55                                                    58 
 56 The following modifications to the I2C protoco     59 The following modifications to the I2C protocol can also be generated by
 57 setting these flags for I2C messages. With the     60 setting these flags for I2C messages. With the exception of I2C_M_NOSTART, they
 58 are usually only needed to work around device      61 are usually only needed to work around device issues:
 59                                                    62 
 60 I2C_M_IGNORE_NAK:                                  63 I2C_M_IGNORE_NAK:
 61     Normally message is interrupted immediatel     64     Normally message is interrupted immediately if there is [NA] from the
 62     client. Setting this flag treats any [NA]      65     client. Setting this flag treats any [NA] as [A], and all of
 63     message is sent.                               66     message is sent.
 64     These messages may still fail to SCL lo->h     67     These messages may still fail to SCL lo->hi timeout.
 65                                                    68 
 66 I2C_M_NO_RD_ACK:                                   69 I2C_M_NO_RD_ACK:
 67     In a read message, master A/NA bit is skip     70     In a read message, master A/NA bit is skipped.
 68                                                    71 
 69 I2C_M_NOSTART:                                     72 I2C_M_NOSTART:
 70     In a combined transaction, no 'S Addr Wr/R     73     In a combined transaction, no 'S Addr Wr/Rd [A]' is generated at some
 71     point. For example, setting I2C_M_NOSTART      74     point. For example, setting I2C_M_NOSTART on the second partial message
 72     generates something like::                     75     generates something like::
 73                                                    76 
 74       S Addr Rd [A] [Data] NA Data [A] P           77       S Addr Rd [A] [Data] NA Data [A] P
 75                                                    78 
 76     If you set the I2C_M_NOSTART variable for      79     If you set the I2C_M_NOSTART variable for the first partial message,
 77     we do not generate Addr, but we do generat     80     we do not generate Addr, but we do generate the start condition S.
 78     This will probably confuse all other clien     81     This will probably confuse all other clients on your bus, so don't
 79     try this.                                      82     try this.
 80                                                    83 
 81     This is often used to gather transmits fro     84     This is often used to gather transmits from multiple data buffers in
 82     system memory into something that appears      85     system memory into something that appears as a single transfer to the
 83     I2C device but may also be used between di     86     I2C device but may also be used between direction changes by some
 84     rare devices.                                  87     rare devices.
 85                                                    88 
 86 I2C_M_REV_DIR_ADDR:                                89 I2C_M_REV_DIR_ADDR:
 87     This toggles the Rd/Wr flag. That is, if y     90     This toggles the Rd/Wr flag. That is, if you want to do a write, but
 88     need to emit an Rd instead of a Wr, or vic     91     need to emit an Rd instead of a Wr, or vice versa, you set this
 89     flag. For example::                            92     flag. For example::
 90                                                    93 
 91       S Addr Rd [A] Data [A] Data [A] ... [A]      94       S Addr Rd [A] Data [A] Data [A] ... [A] Data [A] P
 92                                                    95 
 93 I2C_M_STOP:                                        96 I2C_M_STOP:
 94     Force a stop condition (P) after the messa     97     Force a stop condition (P) after the message. Some I2C related protocols
 95     like SCCB require that. Normally, you real     98     like SCCB require that. Normally, you really don't want to get interrupted
 96     between the messages of one transfer.          99     between the messages of one transfer.
                                                      

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