Serial data output hangs if Buffered Serial is enabled

[maclobdell]

Describe the bug

If the platform.stdio-buffered-serial feature is enabled in _mbedapp.json, then the system will typically hang some indeterminate time after the Pelion Client is initialized.

"platform.stdio-buffered-serial"            : true,

Normally, enabling buffered serial can result in better stability. But in this case, it causes either the system or just the serial output to crash.

By default we have turned off Buffered Serial until this issue can be resolved. At that point it should be re-enabled.

Things I've investigated

• I see the issue regardless of if ENABLE_CY_FACTORY_FLOW is enabled or not.

• I also see it regardless if EXPERIMENTAL_API which I think enables PSA APIs for crypto operations.

• Also doubling rtos.thread-user-stack-size doesn't seem to make a difference.

• I created a simpler example application which has 4 threads that each print lots of data to the serial port at different intervals, and one thread that downloads data from a socket. I never see the issue. However, it is easy to reproduce with the cloud client example application.

• I haven't been able to get the debugger to connect to debug it further.

To Reproduce Steps to reproduce the behavior:

1. Set "platform.stdio-buffered-serial" to true
2. Follow the other steps in the readme to build and run the application.
3. See error

Expected behavior It should not hang.

Logs none

Host system (please complete the following information):

• OS: [Windows x.y, Ubuntu x.y, ...]
• Compiler: Arm Compiler
• Compiler version: 6.14
• Mbed CLI version (if used): Tested with Mbed Studio

Device information:

• Device: CY8CKIT-064B0S2-4343W (using build target CYTFM_064B0S2_4343W)
• OS: Mbed 6.2.1
• Client version: 4.6.0
• Other SW: n/a

Additional context none

[ifyall]

@maclobdell, do you know if this only impacts the PSoC 064 board, or is it seen in PSoC 062 boards as well?

Thank you in advance,

Ian

[moshe-shahar]

I think it was not tested on PSoC 062. It was faster to reproduce it if the profile was debug (mbed compile --profile debug) and traces were enabled.

Also, I was using ModusToolbox 2.1 for the debugger but I couldn't reproduce it when the debugger was connected.