Open Source M-bus (Meter-Bus) Library

libmbus is an open source library for the M-bus (Meter-Bus) protocol.

The Meter-Bus is a standard for reading out meter data from electricity meters, heat meters, gas meters, etc. The M-bus standard deals with both the electrical signals on the M-Bus, and the protocol and data format used in transmissions on the M-Bus. The role of libmbus is to decode/encode M-bus data, and to handle the communication with M-Bus devices.

Wired M-Bus Specification (v4.8):

• https://m-bus.com/documentation-wired/01-introduction
• https://m-bus.com/assets/downloads/MBDOC48.PDF

Manufacturer ID list:

• https://www.m-bus.de/man.html

Example M-Bus Master:

• https://github.com/addiva-elektronik/mbus-master

Example M-Bus Device (slave):

• https://github.com/addiva-elektronik/mbus-device

Building

./autogen.sh             # only needed from git clone
./configure
make

Note: libmbus relies on the math function pow() so when you link it with your own program ensure you have -lm. When using pkg-config to query the system for appropriate CFLAGS and LIBS, this is handled automatically for you. However, when building on an embedded system you may not have pow(), to this end a replacement is available in lib/pow.c.

Memory Usage

The library is fairly conservative with RAM, below is a run using an example M-Bus master that talks to an example M-Bus device over a virtual serial bus. Memory usage has been analyzed with the valgrind tool massif.

An example run where the master sends a data request to the device and prints it in verbose format (default: raw HEX dump), toggles to XML output and does the same request.

Note: below stack usage in this run peaks at 4416 bytes, which was determined to occur in the C runtime (crt0) well before the main() function is started. In some runs the stack peaked in crt0 at 7736 bytes (!) before falling back to reasonable levels in main().

$ ./vsb -n 2 & sleep 1
vsb: device 1 => /dev/pts/8
vsb: device 2 => /dev/pts/9
$ ../mbus-device/mbus-device -a 5 /dev/pts/9 -f ~/src/libmbus/test/test-frames/abb_delta.hex &
$ valgrind --tool=massif --stacks=yes ./mbus-master /dev/pts/8 -v
...
> req 5
...
> xml
> req 5
...
$ ms_print massif.out.842178
--------------------------------------------------------------------------------
  n        time(i)         total(B)   useful-heap(B) extra-heap(B)    stacks(B)
--------------------------------------------------------------------------------
  0              0                0                0             0            0
  1          2,598              512                0             0          512
  2         40,725              512                0             0          512
  3         51,678            1,520                0             0        1,520
  4         75,611            4,416                0             0        4,416
  5         92,251            1,376                0             0        1,376
... before main() has started, inside crt0.o somewhere, seen up to 7,736 stack!
 37        720,368           21,016           17,019           301        3,696
 38        737,529           25,496           23,006           346        2,144
 39        755,851           22,672           18,520           400        3,752
...
 52        960,449           21,552           18,520           400        2,632
...
 63        989,236            5,776            3,728           152        1,896
 64        991,834            4,136            3,549           115          472
 65        994,435              504                0             0          504
--------------------------------------------------------------------------------

Origin & References

This is a fork of the upstream https://github.com/rscada/libmbus project with a focus on porting to microcontrollers running real-time operating systems like Zephyr.

libmbus is originally from Raditex Control, see their original page at http://www.rscada.se/libmbus.