nuttx-apps/modbus/README.md

# Modbus

This directory contains a port of last open source version of FreeModBus (BSD
license). The code in this directory is a subset of FreeModBus version 1.5.0
(June 6, 2010) that can be downloaded in its entirety from
http://developer.berlios.de/project/showfiles.php?group_id=6120.

Includes extensions to support RTU master mode by Armink(383016632@qq.com):
https://github.com/armink/FreeModbus_Slave-Master-RTT-STM32. Ported to NuttX by
Darcy Gong.

## Directory Structure / Relation to freemodbus-v1.5.0

The original FreeModBus download consists of several directories. This subset
takes only the contents of one directory, `modbus/`, that implements the core
modbus logic and integrates that directory into the NuttX build system. The
mapping between `freemodbus-v1.5.0` and the nuttx directories is shown below:

```
--------------------------- ----------------------------------------------
freemodbus-v1.5.0           NuttX
--------------------------- ----------------------------------------------
All top level .txt files    Not included
demo/                       Not included. This directory contains demo
                            and porting code for a variety of platforms.
                            The NuttX demo was ported from the LINUX
                            demo in this directory and can be found at
                            apps/examples/modbus.
doc/                        Not included. This directory contains Doxygen
                            support files.
modbus/                     Included in its entirety in various locations:
        ascii                  apps/modbus/ascii
        functions              apps/modbus/functions
        include                apps/include/modbus
        mb.c                   apps/modbus/mb.c
        rtu                    apps/modbus/rtu
        tcp                    apps/modbus/tcp
tools/                      Not included. This directory contains Doxygen
                            tools.
--------------------------- ----------------------------------------------
```

So this directory is equivalent to the `freemodbus-v1.5.0/modbus` directory
except that (1) it may include modifications for the integration with NuttX and
(2) the modbus/include directory was moved to `apps/modbus`.

The original, unmodified `freemodbus-v1.5.0` was checked in as SVN revision
`4960`.

The other directory here, `nuttx/`, implements the NuttX modbus interface. It
derives from the `freemodbus-v1.5.0/demo/LINUX/port` directory.

## Configuration Options

In the original `freemodbus-v1.5.0` release, the FreeModBus configuration was
controlled by the header file `mbconfig.h`. This header file was eliminated
(post revision `4960`) and the FreeModBus configuration was integrated into the
NuttX configuration system.

The NuttX-named configuration options that are available include:

- `CONFIG_MODBUS` – General ModBus support.
- `CONFIG_MB_ASCII_ENABLED` – Modbus ASCII support.
- `CONFIG_MB_ASCII_MASTER` – Modbus ASCII master support.
- `CONFIG_MB_RTU_ENABLED` – Modbus RTU support.
- `CONFIG_MB_RTU_MASTER` – Modbus RTU master support.
- `CONFIG_MB_TCP_ENABLED` – Modbus TCP support.
- `CONFIG_MB_ASCII_TIMEOUT_SEC` – Character timeout value for Modbus ASCII. The
  character timeout value is not fixed for Modbus ASCII and is therefore a
  configuration option. It should be set to the maximum expected delay time of
  the network. Default: `1`.
- `CONFIG_MB_ASCII_TIMEOUT_WAIT_BEFORE_SEND_MS` – Timeout to wait in ASCII prior
  to enabling transmitter. If defined the function calls `vMBPortSerialDelay`
  with the argument `CONFIG_MB_ASCII_TIMEOUT_WAIT_BEFORE_SEND_MS` to allow for a
  delay before the serial transmitter is enabled. This is required because some
  targets are so fast that there is no time between receiving and transmitting
  the frame. If the master is too slow with enabling its receiver then it will
  not receive the response correctly.
- `CONFIG_MB_FUNC_HANDLERS_MAX` – Maximum number of Modbus functions codes the
  protocol stack should support. The maximum number of supported Modbus
  functions must be greater than the sum of all enabled functions in this file
  and custom function handlers. If set too small, adding more functions will
  fail.
- `CONFIG_MB_FUNC_OTHER_REP_SLAVEID_BUF` – Number of bytes which should be
  allocated for the Report Slave ID command. This number limits the maximum size
  of the additional segment in the report slave id function. See
  `eMBSetSlaveID()` for more information on how to set this value. It is only
  used if `CONFIG_MB_FUNC_OTHER_REP_SLAVEID_ENABLED` is set to `1`.
- `CONFIG_MB_FUNC_OTHER_REP_SLAVEID_ENABLED` – If the Report Slave ID function
  should be enabled.
- `CONFIG_MB_FUNC_READ_INPUT_ENABLED` – If the Read Input Registers function
  should be enabled.
- `CONFIG_MB_FUNC_READ_HOLDING_ENABLED` – If the Read Holding Registers function
  should be enabled.
- `CONFIG_MB_FUNC_WRITE_HOLDING_ENABLED` – If the Write Single Register function
  should be enabled.
- `CONFIG_MB_FUNC_WRITE_MULTIPLE_HOLDING_ENABLED` – If the Write Multiple
  registers function should be enabled.
- `CONFIG_MB_FUNC_READ_COILS_ENABLED` – If the Read Coils function should be
  enabled.
- `CONFIG_MB_FUNC_WRITE_COIL_ENABLED` – If the Write Coils function should be
  enabled.
- `CONFIG_MB_FUNC_WRITE_MULTIPLE_COILS_ENABLED` – If the Write Multiple Coils
  function should be enabled.
- `CONFIG_MB_FUNC_READ_DISCRETE_INPUTS_ENABLED` – If the Read Discrete Inputs
  function should be enabled.
- `CONFIG_MB_FUNC_READWRITE_HOLDING_ENABLED` – If the Read/Write Multiple
  Registers function should be enabled.

See also other serial settings, in particular:

- `CONFIG_SERIAL_TERMIOS` – Serial driver supports `termios.h` interfaces
  If this is not defined, then the terminal settings (baud, parity, etc.)
  are not configurable at runtime.

## Note

The developer of FreeModBus, Christian Walter, is still developing Modbus
libraries, although they are now commercial. See
http://www.embedded-solutions.at/ for further information.