diff options
Diffstat (limited to 'Documentation/i2c/i2c-protocol')
| -rw-r--r-- | Documentation/i2c/i2c-protocol | 38 |
1 files changed, 25 insertions, 13 deletions
diff --git a/Documentation/i2c/i2c-protocol b/Documentation/i2c/i2c-protocol index 10518dd5881..ff6d6cee6c7 100644 --- a/Documentation/i2c/i2c-protocol +++ b/Documentation/i2c/i2c-protocol @@ -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. @@ -49,9 +49,20 @@ a byte read, followed by a byte write: Modified transactions ===================== -We have found some I2C devices that needs the following modifications: +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: @@ -60,17 +71,18 @@ We have found some I2C devices that needs the following modifications: 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. - Flags I2C_M_REV_DIR_ADDR + 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 - 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. |