Add ports/zephyr/ BACnet/IP datalink port

[salimzedni]

Summary
The bacnet-stack is packaged as a Zephyr module, but there is no corresponding ports/zephyr/ datalink implementation for BACnet/IP. The existing ports (ports/linux/bip-init.c, ports/bsd/bip-init.c) pull in Linux/BSD-specific headers (asm/types.h, ifaddrs.h) that do not exist in the Zephyr build environment, causing a compile failure.

Current behaviour
When including bacnet-stack as a Zephyr west module and attempting to use BACnet/IP, the build fails:

fatal error: ifaddrs.h: No such file or directory

Expected behaviour
BACnet/IP should build and run on Zephyr using its native networking APIs.

What I did
I implemented a bip-init.c for Zephyr using its BSD socket compatibility layer (zsock_socket, zsock_bind, zsock_setsockopt) and net_if_get_default() to obtain the assigned IP address.

This has been tested on an NXP i.MX RT1020 with CONFIG_NET_SOCKETS=y, and successfully initializes the BACnet/IP datalink.

Contribution
I can open a PR adding a ports/zephyr/ implementation if this aligns with the project direction.

Environment

• Zephyr version: main (commit 79ce80e73c30)
• Board: NXP i.MX RT1020
• bacnet-stack-zephyr commit: c1f1c1e
• bacnet-stack core version: 1.5.0 (bacnet-stack-1.5.0-25-g5d73544a)

[salimzedni]

The BACnet/IP Zephyr port exists at:
zephyr/subsys/bacnet_datalink/bip-init.c

However it is completely undiscoverable because:

1. It is not in ports/zephyr/ where every other platform port lives
2. There is no documentation pointing to it
3. The existing ports/linux/ and ports/bsd/ are still present and
   will be picked up first, causing build failures with:
   fatal error: ifaddrs.h: No such file or directory

Suggestion:

• Add a ports/zephyr/ symlink or README pointing to the actual location
• Remove or guard ports/linux/ and ports/bsd/ from Zephyr builds
• Add documentation explaining CONFIG_BACNETSTACK=y pulls in the
  correct bip-init.c automatically

[skarg]

Thank you for reviewing the development process and missing documentation that I don't see when I'm immersed in the code that I know. I'd be happy to review a pull request with the details that you expected.

[salimzedni]

Hi Steve,

After further investigation I actually found that the BACnet/IP Zephyr port already exists at:

zephyr/subsys/bacnet_datalink/bip-init.c

The issue is purely discoverability — when trying to use BACnet/IP on Zephyr, the natural place to look is ports/ alongside the other platform ports (linux, bsd, esp32 etc.). Since there is no ports/zephyr/ directory, it appears as though no Zephyr port exists, leading to attempts to use ports/linux/ or ports/bsd/ which fail with missing system headers.

So rather than a new implementation, I think the fix is simply documentation — either a note in the README pointing to zephyr/subsys/bacnet_datalink/bip-init.c, or a small mention in ports/ explaining that the Zephyr datalink implementation lives in the Zephyr subsystem.

Happy to submit a PR with a documentation update if that works for you.

Thank you for your work on the stack!