Serialize access to the CRC peripheral (STM32F2xx)

[sergeuz]

Problem

The CRC peripheral is not thread-safe and thus concurrent hardware-accelerated CRC calculations should be serialized.

While there's no evidence that the system and application threads perform CRC calculations concurrently, a synthetic test shows that such a situation can cause invalidation of the DCT.

Solution

Guard the platform's Compute_CRC32() function with a global lock.

Steps to Test

• wiring/no_fixture: CONCURRENT_02*

References

• [CH10651]

Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[m-mcgowan]

Would be good with some tests too to demonstrate the thread safety.

[sergeuz]

Would be good with some tests too to demonstrate the thread safety

I'll strip that DCT stress test application which I used to reproduce the issue and turn it into a test app 👍