tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
Documentation: i2c: improve section about flags mangling the protocol
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>
+20
-15
+20
-15
Documentation/i2c/i2c-protocol
+20
-15
Documentation/i2c/i2c-protocol
···
6
6
S (1 bit) : Start bit
7
7
P (1 bit) : Stop bit
8
8
Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0.
9
-
A, NA (1 bit) : Accept and reverse accept bit.
10
-
Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to
9
+
A, NA (1 bit) : Accept and reverse accept bit.
10
+
Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to
11
11
get a 10 bit I2C address.
12
12
Comm (8 bits): Command byte, a data byte which often selects a register on
13
13
the device.
···
49
49
Modified transactions
50
50
=====================
51
51
52
-
The following modifications to the I2C protocol can also be generated,
53
-
with the exception of I2C_M_NOSTART these are usually only needed to
54
-
work around device issues:
52
+
The following modifications to the I2C protocol can also be generated by
53
+
setting these flags for i2c messages. With the exception of I2C_M_NOSTART, they
54
+
are usually only needed to work around device issues:
55
55
56
-
Flag I2C_M_NOSTART:
56
+
I2C_M_IGNORE_NAK:
57
+
Normally message is interrupted immediately if there is [NA] from the
58
+
client. Setting this flag treats any [NA] as [A], and all of
59
+
message is sent.
60
+
These messages may still fail to SCL lo->hi timeout.
61
+
62
+
I2C_M_NO_RD_ACK:
63
+
In a read message, master A/NA bit is skipped.
64
+
65
+
I2C_M_NOSTART:
57
66
In a combined transaction, no 'S Addr Wr/Rd [A]' is generated at some
58
67
point. For example, setting I2C_M_NOSTART on the second partial message
59
68
generates something like:
···
76
67
I2C device but may also be used between direction changes by some
77
68
rare devices.
78
69
79
-
Flags I2C_M_REV_DIR_ADDR
70
+
I2C_M_REV_DIR_ADDR:
80
71
This toggles the Rd/Wr flag. That is, if you want to do a write, but
81
72
need to emit an Rd instead of a Wr, or vice versa, you set this
82
73
flag. For example:
83
74
S Addr Rd [A] Data [A] Data [A] ... [A] Data [A] P
84
75
85
-
Flags I2C_M_IGNORE_NAK
86
-
Normally message is interrupted immediately if there is [NA] from the
87
-
client. Setting this flag treats any [NA] as [A], and all of
88
-
message is sent.
89
-
These messages may still fail to SCL lo->hi timeout.
90
-
91
-
Flags I2C_M_NO_RD_ACK
92
-
In a read message, master A/NA bit is skipped.
76
+
I2C_M_STOP:
77
+
Force a stop condition (P) after the message. Some I2C related protocols
78
+
like SCCB require that. Normally, you really don't want to get interrupted
79
+
between the messages of one transfer.