px4-firmware/apps/system/i2c/README.txt

README File for the I2C Tool
============================

The I2C tool provides a way to debug I2C related problems.  This README file
will provide usage information for the I2C tools.

CONTENTS
========

  o System Requirements
    - I2C Driver
    - Configuration Options
  o Help
  o Common Line Form
  o Common Command Options
    - "Sticky" Options
    - Environment variables
    - Common Option Summary
  o Command summary
    - bus
    - dev
    - get
    - set
    - verf
  o I2C Build Configuration
    - NuttX Configuration Requirements
    - I2C Tool Configuration Options

System Requirements
===================

I2C Driver
----------
In order to use the I2C driver, you system -- in particular, your I2C driver --
must meet certain requirements:

1. It support calling up_i2cinitialize() numerous times, resetting the I2C
   hardware on each (initial) time.  up_i2cuninitialize() will be called after
   each call to up_i2cinitialize() to free any resources and disable the I2C.
2. up_i2cinitialize must accept any interface number without crashing.  It
   must simply return NULL if the device is not supported.
3. The I2C driver must support the transfer method (CONFIG_I2C_TRANSFER=y).

The I2C tool is designed to be implemented as a NuttShell (NSH) add-on.  Read
the apps/nshlib/README.txt file for information about add-ons.

Configuration Options
---------------------
CONFIG_I2CTOOL_BUILTIN - Build the tools as an NSH built-in command
CONFIG_I2CTOOL_MINBUS - Smallest bus index supported by the hardware (default 0).
CONFIG_I2CTOOL_MAXBUS - Largest bus index supported by the hardware (default 3)
CONFIG_I2CTOOL_MINADDR - Minium device address (default: 0x03)
CONFIG_I2CTOOL_MAXADDR - Largest device address (default: 0x77)
CONFIG_I2CTOOL_MAXREGADDR - Largest register address (default: 0xff)
CONFIG_I2CTOOL_DEFFREQ - Default frequency (default: 4000000)

HELP
====

First of all, the I2C tools supports a pretty extensive help output.  That
help output can be view by entering either:

  nsh> i2c help

or

  nsh> i2c ?

Here is an example of the help output.  I shows the general form of the
command line, the various I2C commands supported with their unique command
line options, and a more detailed summary of the command I2C command
options.

  nsh> i2c help
  Usage: i2c <cmd> [arguments]
  Where <cmd> is one of:

    Show help     : ?
    List buses    : bus
    List devices  : dev [OPTIONS] <first> <last>
    Read register : get [OPTIONS] [<repititions>]
    Show help     : help
    Write register: set [OPTIONS] <value> [<repititions>]
    Verify access : verf [OPTIONS] <value> [<repititions>]

  Where common "sticky" OPTIONS include:
    [-a addr] is the I2C device address (hex).  Default: 03 Current: 03
    [-b bus] is the I2C bus number (decimal).  Default: 1 Current: 1
    [-r regaddr] is the I2C device register address (hex).  Default: 00 Current: 00
    [-w width] is the data width (8 or 16 decimal).  Default: 8 Current: 8
    [-s|n], send/don't send start between command and data.  Default: -n Current: -n
    [-i|j], Auto increment|don't increment regaddr on repititions.  Default: NO Current: NO
    [-f freq] I2C frequency.  Default: 100000 Current: 100000

  NOTES:
  o An environment variable like $PATH may be used for any argument.
  o Arguments are "sticky".  For example, once the I2C address is
    specified, that address will be re-used until it is changed.

  WARNING:
  o The I2C dev command may have bad side effects on your I2C devices.
    Use only at your own risk.

COMMAND LINE FORM
=================

The I2C is started from NSH by invoking the 'i2c' command from the NSH
command line. The general form of the 'i2c' command is:

  i2c <cmd> [arguments]

Where <cmd> is a "sub-command" and identifies one I2C operations supported
by the tool.  [arguments] represents the list of arguments needed to perform
the I2C operation.  Those arguments vary from command to command as
described below.  However, there is also a core set of common OPTIONS
supported by all commands.  So perhaps a better representation of the
general I2C command would be:

  i2c <cmd> [OPTIONS] [arguments]

Where [OPTIONS] represents the common options and and arguments represent
the operation-specific arguments.

COMMON COMMAND OPTIONS
======================

"Sticky" Options
----------------
In order to interact with I2C devices, there are a number of I2C parameters
that must be set correctly.  One way to do this would be to provide to set
the value of each separate command for each I2C parameter.  The I2C tool
takes a different approach, instead:  The I2C configuration can be specified
as a (potentially long) sequence of command line arguments.

These arguments, however, are "sticky."  They are sticky in the sense that
once you set the I2C parameter, that value will remain until it is reset
with a new value (or until you reset the board).

Environment Variables
---------------------
NOTE also that if environment variables are not disabled (by
CONFIG_DISABLE_ENVIRON=y), then these options may also be environment
variables.  Environment variables must be preceded with the special
character $.  For example, PWD is the variable that holds the current
working directory and so $PWD could be used as a command line argument.  The
use of environment variables on the I2C tools command is really only useful
if you wish to write NSH scripts to execute a longer, more complex series of
I2C commands.

Common Option Summary
---------------------

[-a addr] is the I2C device address (hex).  Default: 03 Current: 03

  The [-a addr] sets the I2C device address.  The valid range is 0x03
  through 0x77 (this valid range is controlled by the configuration settings
  CONFIG_I2CTOOL_MINADDR and CONFIG_I2CTOOL_MAXADDR).  If you are working
  with the same device, the address needs to be set only once.
  
  All I2C address are 7-bit, hexadecimal values.

  NOTE 1: Notice in the "help" output above it shows both default value of
  the I2C address (03 hex) and the current address value (also 03 hex).

  NOTE 2: Sometimes I2C addresses are represented as 8-bit values (with
  bit zero indicating a read or write operation).  The I2C tool uses a
  7-bit representation of the address with bit 7 unused and no read/write
  indication in bit 0.  Essentially, the 7-bit address is like the 8-bit
  address shifted right by 1.

  NOTE 3: Most I2C bus controllers will also support 10-bit addressing.
  That capability has not been integrated into the I2C tool as of this
  writing.

[-b bus] is the I2C bus number (decimal).  Default: 1 Current: 1

  Most devices support multiple I2C devices and also have unique bus
  numbering.  This option identifies which bus you are working with now.
  The valid range of bus numbers is controlled by the configuration settings
  CONFIG_I2CTOOL_MINBUS and CONFIG_I2CTOOL_MAXBUS.
  
  The bus numbers are small, decimal numbers.

[-r regaddr] is the I2C device register address (hex).  Default: 00 Current: 00

  The I2C set and get commands will access registers on the I2C device.  This
  option selects the device register address (sometimes called the sub-address).
  This is an 8-bit hexadecimal value.  The maximum value is determined by
  the configuration setting CONFIG_I2CTOOL_MAXREGADDR.

[-w width] is the data width (8 or 16 decimal).  Default: 8 Current: 8

  Device register data may be 8-bit or 16-bit.  This options selects one of
  those two data widths.

[-s|n], send/don't send start between command and data.  Default: -n Current: -n

  This determines whether or not there should be a new I2C START between
  sending of the register address and sending/receiving of the register data.

[-i|j], Auto increment|don't increment regaddr on repititions.  Default: NO Current: NO

  On commands that take a optional number of repetitions, the option can be
  used to temporarily increment the regaddr value by one on each repitition.

[-f freq] I2C frequency.  Default: 400000 Current: 400000

  The [-f freq] sets the frequency of the I2C device.

COMMAND SUMMARY
===============

We have already seen the I2C help (or ?) commands above.  This section will
discuss the remaining commands.

List buses: bus [OPTIONS]
--------------------------

This command will simply list all of the configured I2C buses and indicate
which are supported by the driver and which are not:
  
   BUS   EXISTS?
  Bus 1: YES
  Bus 2: NO

The valid range of bus numbers is controlled by the configuration settings
CONFIG_I2CTOOL_MINBUS and CONFIG_I2CTOOL_MAXBUS.

List devices: dev [OPTIONS] <first> <last>
------------------------------------------

The 'dev' command will attempt to identify all of the I2C devices on the
selected bus.  The <first> and <last> arguments are 7-bit, hexadecimal
I2C addresses.  This command will examine a range of addresses beginning
with <first> and continuing through <last>.  It will request the value
of register zero from each device.

If the device at an address responds, then this command will display the
address of the device.  If the device does not respond, this command will
display "--".  The resulting display is like:

nsh> i2c dev 03 77
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- 49 -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

WARNINGS:
  o The I2C dev command may have bad side effects on certain I2C devices.
    For example, if could cause data loss in an EEPROM device.
  o The I2C dev command also depends upon the underlying behavior of the
    I2C driver.  How does the driver respond to addressing failures?

Read register: get [OPTIONS]
----------------------------

  This command will read the value of the I2C register using the selected
  I2C parameters in the common options.  No other arguments are required.
  
  This command with write the 8-bit address value then read an 8- or 16-bit
  data value from the device.  Optionally, it may re-start the transfer
  before obtaining the data.

  An optional <repititions> argument can be supplied to repeat the
  read operation an arbitrary number of times (up to 2 billion).  If
  auto-increment is select (-i), then the register address will be
  temporarily incremented on each repitions.  The increment is temporary
  in the since that it will not alter the "sticky" value of the
  register address.

  On success, the output will look like the following (the data value
  read will be shown as a 4-character hexadecimal number if the 16-bit
  data width option is selected).

  READ Bus: 1 Addr: 49 Subaddr: 04 Value: 96

  All values (except the bus numbers) are hexadecimal.

Write register: set [OPTIONS] <value>
-------------------------------------

  This command will write a value to an I2C register using the selected
  I2C parameters in the common options.  The value to write must be provided
  as the final, hexadecimal value.  This value may be an 8-bit value (in the
  range 00-ff) or a 16-bit value (in the range 0000-ffff), depending upon
  the selected data width.
  
  This command will write the 8-bit address value then write the 8- or 16-bit
  data value to the device.  Optionally, it may re-start the transfer
  before writing the data.

  An optional <repititions> argument can be supplied to repeat the
  write operation an arbitrary number of times (up to 2 billion).  If
  auto-increment is select (-i), then the register address will be
  temporarily incremented on each repitions.  The increment is temporary
  in the since that it will not alter the "sticky" value of the
  register address.

  On success, the output will look like the following (the data value
  written will be shown as a 4-character hexadecimal number if the 16-bit
  data width option is selected).

  WROTE Bus: 1 Addr: 49 Subaddr: 04 Value: 96

  All values (except the bus numbers) are hexadecimal.

Verify access : verf [OPTIONS] <value> [<repititions>]
------------------------------------------------------

  This command combines writing and reading from an I2C device register.
  It will write a value to an will write a value to an I2C register using
  the selected I2C parameters in the common options just as described for
  tie 'set' command.  Then this command will read the value back just
  as described with the 'get' command.  Finally, this command will compare
  the value read and against the value written and emit an error message
  if they do not match.

  If no value is provided, then this command will use the register address
  itself as the data, providing for a address-in-address test.

  An optional <repititions> argument can be supplied to repeat the
  verify operation an arbitrary number of times (up to 2 billion).  If
  auto-increment is select (-i), then the register address will be
  temporarily incremented on each repitions.  The increment is temporary
  in the since that it will not alter the "sticky" value of the
  register address.

  On success, the output will look like the following (the data value
  written will be shown as a 4-character hexadecimal number if the 16-bit
  data width option is selected).

  VERIFY Bus: 1 Addr: 49 Subaddr: 04 Wrote: 96 Read: 92 FAILURE

  All values (except the bus numbers) are hexadecimal.

I2C BUILD CONFIGURATION
=======================

NuttX Configuration Requirements
--------------------------------
The I2C tools requires the following in your NuttX configuration:

1. Device-specific I2C support must be enabled.  The I2C tool will call the
   platform-specific function up_i2cinitialize() to get instances of the
   I2C interface and the platform-specific function up_i2cuninitialize()
   to discard instances of the I2C interface.

   NOTE 1: The I2C interface is defined in include/nuttx/i2c.h.

   NOTE 2: This I2C tool uses direct I2C device interfaces.  As such, it
   relies on internal OS interfaces that are not normally available to a
   user-space program.  As a result, the I2C tool cannot be used if a
   NuttX is built as a protected, supervisor kernel (CONFIG_NUTTX_KERNEL).

2. I2C driver configuration

   The CONFIG_I2C_TRANSFER option must also be set in your NuttX
   configuration.  This configuration is the defconfig file in your
   configuration directory that is copied to the NuttX top-level
   directory as .config when NuttX is configured.

     CONFIG_I2C_TRANSFER=y

   NOTE:  CONFIG_I2C_TRANSFER adds extra methods to the I2C interface.
   Not all I2C interfaces support these extra methods.  If your platform's
   I2C driver does not support these extra methods, then you cannot use
   the I2C tool unless you extend the support in your platform I2C
   driver.

3. Application configuration.

   The path to the I2C tool directory must also be set in your NuttX
   application configuration.  This application configuration is the
   appconfig file in your configuration directory that is copied to the
   NuttX application directory as .config when NuttX is configured.

     CONFIGURE_APPS += system/i2c

I2C Tool Configuration Options
------------------------------

The default behavior of the I2C tool can be modified by the setting the
options in the NuttX configuration.  This configuration is the defconfig
file in your configuration directory that is copied to the NuttX top-level
directory as .config when NuttX is configured.

  CONFIG_I2CTOOL_BUILTIN: Build the tools as an NSH built-in command
  CONFIG_I2CTOOL_MINBUS: Smallest bus index supported by the hardware (default 0).
  CONFIG_I2CTOOL_MAXBUS: Largest bus index supported by the hardware (default 3)
  CONFIG_I2CTOOL_MINADDR: Minium device address (default: 0x03)
  CONFIG_I2CTOOL_MAXADDR: Largest device address (default: 0x77)
  CONFIG_I2CTOOL_MAXREGADDR: Largest register address (default: 0xff)
  CONFIG_I2CTOOL_DEFFREQ: Default frequency (default: 4000000)