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Zephyr Behaviour Tree - Subtree Reuse

Overview

This sample validates the correct behavior tree traversal when a subtree is used multiple times. It reproduces the scenario from GitHub issue #28 where incorrect indices caused nodes to be skipped during execution.

The behavior tree structure is:

Sequence
├── SubTree (btree_subtree) → sub
├── A
├── SubTree (btree_subtree) → sub
└── B

The expected execution order is: sub → A → sub → B

Prior to the fix, the second instance of the subtree had incorrect sibling indices, causing node A to be skipped entirely.

Building and Running

This application can be built and executed on qemu_cortex_m3 as follows:

west build -p -b qemu_cortex_m3 samples/subsys/zephyrbt/subtree_reuse -t run

To build for another board, change "qemu_cortex_m3" above to that board's name.

Sample Output

*** Booting Zephyr OS ***
D: zephyrbt_action_sub_init stub function
D: zephyrbt_action_a_init stub function
D: zephyrbt_action_sub_init stub function
D: zephyrbt_action_b_init stub function
D: tick
D: eval sequence [control, 4]
D: Deep: 1
D: sequence [control, 4]
D: eval sub [action, 3]
D: Deep: 2
D: zephyrbt_action_sub stub function
D: eval a [action, 2]
D: Deep: 2
D: zephyrbt_action_a stub function
D: eval sub [action, 1]
D: Deep: 2
D: zephyrbt_action_sub stub function
D: eval b [action, 0]
D: Deep: 2
D: zephyrbt_action_b stub function

The key verification points are:

  1. All four nodes (sub, a, sub, b) are evaluated in the correct order
  2. Node 'a' is not skipped (which was the bug symptom)
  3. Each subtree instance has a unique index (3 and 1)