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tests: arch: arm_thread_swap: add README file

The commit adds a README file with a description of the test.

Signed-off-by: Ioannis Glaropoulos <>
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ioannisg authored and nashif committed Jul 10, 2019
1 parent 0f7e485 commit 524300a98bd6ab57f43806ef7394145e5b5e88ac
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Title: Test to verify the thread-swap (context-switch) mechanism (ARM Only)


This test verifies that the ARM thread context-switch mechanism
behaves as expected. In particular, the test verifies that:
- the callee-saved registers are saved and restored, properly,
at thread swap-out and swap-in, respectively
- the floating-point callee-saved registers are saved and
restored, properly, at thread swap-out and swap-in, respectively,
when the thread is using the floating-point registers
- the thread execution priority (BASEPRI) is saved and restored,
properly, at thread context-switch
- the swap return value can be set and will be return, properly,
at thread swap-in
- the mode variable (when building with support for either user
space or FP shared registers) is saved and restored properly.

The test verifies the correct behavior of the thread contex-switch,
when it is triggered indirectly (by setting the PendSV interrupt
to pending state), as well as when the thread itself triggers its
swap-out (by calling __swap(.)).

The test is currently supported only in ARMv7-M and ARMv8-M Mainline


Building and Running Project:

This project outputs to the console. It can be built and executed on QEMU as

ninja/make run



Problems caused by out-dated project information can be addressed by
issuing one of the following commands then rebuilding the project:

ninja/make clean # discard results of previous builds
# but keep existing configuration info
ninja/make pristine # discard results of previous builds
# and restore pre-defined configuration info


Sample Output:

***** Booting Zephyr OS build zephyr-v1.14.0-1726-gb95a71960622 *****
Running test suite arm_thread_swap
starting test - test_arm_thread_swap
PASS - test_arm_thread_swap
Test suite arm_thread_swap succeeded

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