NAME

       i2ctransfer - send user-defined I2C messages in one transfer

SYNOPSIS

       i2ctransfer [-f] [-y] [-v] [-a] i2cbus desc [data] [desc [data]] ...
       i2ctransfer -V

DESCRIPTION

       i2ctransfer  is  a  program  to  create  I2C  messages  and send them combined as one transfer.  For read
       messages, the contents of the received buffers are printed to stdout, one line per read message.
       Please note the difference between a transfer and a message here.  A transfer  may  consist  of  multiple
       messages  and  is  started  with a START condition and ends with a STOP condition as described in the I2C
       specification.  Messages within the transfer are concatenated using the REPEATED START condition which is
       described there as well.  There are some advantages of having multiple messages in one transfer.   First,
       some  devices  keep  their  internal  states for REPEATED START but reset them after a STOP.  Second, you
       cannot get interrupted during one transfer, but it might happen between multiple transfers.  Interruption
       could happen on hardware level by another I2C master on the bus, or at software level by another I2C user
       who got its transfer scheduled between yours.  This program helps you to create proper transfers for your
       needs.

OPTIONS

       -f     Force access to the device even if it is already busy.  By default,  i2ctransfer  will  refuse  to
              access  a  device  which  is  already  under  the  control of a kernel driver.  Using this flag is
              dangerous, it can seriously confuse the kernel driver in question.  It can also cause  i2ctransfer
              to silently write to the wrong register.  So use at your own risk and only if you know what you're
              doing.

       -y     Disable  interactive  mode.   By  default,  i2ctransfer will wait for a confirmation from the user
              before messing with the I2C bus.  When this flag is used, it will perform the operation  directly.
              This is mainly meant to be used in scripts.

       -v     Enable  verbose  output.   It  will  print  infos  about all messages sent, i.e. not only for read
              messages but also for write messages.

       -V     Display the version and exit.

       -a     Allow using addresses between 0x00 - 0x07 and 0x78 - 0x7f. Not recommended.

ARGUMENTS

       The first parameter i2cbus indicates the number or name of the I2C bus to be used.   This  number  should
       correspond to one of the busses listed by i2cdetect -l.

       The  next  parameter is one or multiple desc blocks.  The number of blocks is limited by the Linux Kernel
       and defined by I2C_RDWR_IOCTL_MAX_MSGS (42 as of v4.10).  desc blocks are composed like this:

       {r|w}<length_of_message>[@address]

       {r|w}  specifies if the message is read or write

       <length_of_message>
              specifies the number of bytes read or written in this message.  It is parsed as an unsigned 16 bit
              integer, but note that the Linux Kernel applies an additional upper limit (8192 as of v4.10).  For
              read messages to targets which support SMBus Block transactions, it can  also  be  '?',  then  the
              target will determine the length.

       [@address]
              specifies  the  7-bit  address of the chip to be accessed for this message, and is an integer.  If
              omitted, reuse the previous address.  Normally, addresses  outside  the  range  of  0x08-0x77  and
              addresses  with  a kernel driver attached to them will be blocked.  This can be overridden with -a
              (all) or -f (force).  Be very careful when  using  these!   10-bit  addresses  are  currently  not
              supported at all.

       If  the  I2C  message  is a write, then a data block with the data to be written follows.  It consists of
       <length_of_message> bytes which can be marked with the usual prefixes for hexadecimal,  octal,  etc.   To
       make it easier to create larger data blocks easily, the data byte can have a suffix.

       =      keep value constant until end of message (i.e. 0= means 0, 0, 0, ...)

       +      increase value by 1 until end of message (i.e. 0+ means 0, 1, 2, ...)

       -      decrease value by 1 until end of message (i.e. 0xff- means 0xff, 0xfe, 0xfd, ...)

       p      use value as seed for an 8 bit pseudo random sequence (i.e. 0p means 0x00, 0x50, 0xb0, ...)

EXAMPLES

       On  bus 0, from an EEPROM at address 0x50, read 8 byte from offset 0x64 (first message writes one byte to
       set the memory pointer to 0x64, second message reads from the same chip):
              # i2ctransfer 0 w1@0x50 0x64 r8

       For the same EEPROM, at offset 0x42 write 0xff 0xfe ... 0xf0 (one write  message;  first  byte  sets  the
       memory pointer to 0x42, 0xff is the first data byte, all following data bytes are decreased by one):

              # i2ctransfer 0 w17@0x50 0x42 0xff-

WARNING

       i2ctransfer can be extremely dangerous if used improperly.  It can confuse your I2C bus, cause data loss,
       or  have  more serious side effects.  Writing to a serial EEPROM on a memory DIMM (chip addresses between
       0x50 and 0x57) may DESTROY your memory, leaving your system unbootable!  Be extremely careful using  this
       program.

BUGS

       To report bugs or send fixes, please write to the Linux I2C mailing list <linux-i2c@vger.kernel.org> with
       Cc to the current maintainer: Jean Delvare <jdelvare@suse.de>.

AUTHORS

       Wolfram Sang, based on i2cget by Jean Delvare

       This  manual  page  was originally written by Wolfram Sang based on the manual for i2cset by David Z Maze
       <dmaze@debian.org>.

SEE ALSO

       i2cdetect(8),i2cdump(8),i2cget(8),i2cset(8)

                                                  February 2017                                   i2ctransfer(8)