From ace9429bb58fd418f0c81d4c2835699bddf6bde6 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Thu, 11 Apr 2024 10:27:49 +0200 Subject: Adding upstream version 6.6.15. Signed-off-by: Daniel Baumann --- Documentation/i2c/i2c-protocol.rst | 96 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 96 insertions(+) create mode 100644 Documentation/i2c/i2c-protocol.rst (limited to 'Documentation/i2c/i2c-protocol.rst') diff --git a/Documentation/i2c/i2c-protocol.rst b/Documentation/i2c/i2c-protocol.rst new file mode 100644 index 000000000..df0febfe6 --- /dev/null +++ b/Documentation/i2c/i2c-protocol.rst @@ -0,0 +1,96 @@ +================ +The I2C Protocol +================ + +This document is an overview of the basic I2C transactions and the kernel +APIs to perform them. + +Key to symbols +============== + +=============== ============================================================= +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 to + get a 10 bit I2C address. +Data (8 bits) A plain data byte. + +[..] Data sent by I2C device, as opposed to data sent by the + host adapter. +=============== ============================================================= + + +Simple send transaction +======================= + +Implemented by i2c_master_send():: + + S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P + + +Simple receive transaction +========================== + +Implemented by i2c_master_recv():: + + S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P + + +Combined transactions +===================== + +Implemented by i2c_transfer(). + +They are just like the above transactions, but instead of a stop +condition P a start condition 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 by +setting these flags for I2C messages. With the exception of I2C_M_NOSTART, they +are usually only needed to work around device issues: + +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. + +I2C_M_NO_RD_ACK: + In a read message, master A/NA bit is skipped. + +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 start condition 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. + +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 + +I2C_M_STOP: + Force a stop condition (P) after the message. Some I2C related protocols + like SCCB require that. Normally, you really don't want to get interrupted + between the messages of one transfer. -- cgit v1.2.3