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Documentation: i2c: improve section about flags mangling the protocol

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Sort the entries alphabetically. Make the introductory paragraph more
precise. Skip useless 'Flag' introduction from the entries. Remove
trailing white spaces from the file. Add missing I2C_M_STOP entry.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
This commit is contained in:
Wolfram Sang 2014-04-06 13:37:38 +02:00
parent cf23e33588
commit 9f02fba84b
1 changed files with 20 additions and 15 deletions
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35
Documentation/i2c/i2c-protocol
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@ -6,8 +6,8 @@ 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
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.
@ -49,11 +49,20 @@ a byte read, followed by a byte write:
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:
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:
Flag I2C_M_NOSTART:
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:
@ -67,17 +76,13 @@ work around device issues:
I2C device but may also be used between direction changes by some
rare devices.
Flags I2C_M_REV_DIR_ADDR
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.
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.