Increase priority of network threads for STM32 targets

[martin-kuhn]

Description

• The priority of the TCP/IP thread has been increased from osPriorityNormal to osPriorityHigh.
• The priority of the LWIP thread has been increased from osPriorityNormal to osPriorityHigh.

Motivation and Context

The TCP/IP and the LWIP threads have the same priority as the CLR thread. If the CLR is busy, it's possible that the network communication is interrupted. This leads to a lot of tcp retransmissions and timeout problems.

How Has This Been Tested?

We have tested this on a custom STM32F427 based target with network capabilities, running an application with a modbus over TCP implementation. If the CLR is busy (e.g. during SD-card write or similar), we can see that the low_level_input function is no longer called regularly, which makes that the read function runs into a timeout.

After increasing the priorities, this problem does no longer occur.

We also verified with a stress test, that no problems occur if the data is not read out immediately and the receive buffer is going to be full. The window update mechanism works very well.

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Unit Tests (work on Unit Tests, has no impact on code or features)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[dnfadmin]

All CLA requirements met.

[josesimoes]

Makes sense! Thanks for the improvement. 👍🏻