RTEMS | bsps/arm/stm32f4: Make printk() independent of the console driver. (!1518)

[Catalin Miron (@catalin)]

Catalin Miron created a merge request: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1518

Project:Branches: catalin/rtems:stm32f4_bsp_fix to rtems/rtos/rtems:main
Author: Catalin Miron

## Summary

BSP_output_char used Console_Port_Tbl, which is only allocated by the legacy console_initialization(). With the simple console driver (e.g testsuites/samples/hello) or for any printk() before device driver initialization this resulted in a NULL pointer dereference. The USART was also never initialized in this case.

Fall back to Console_Configuration_Ports while Console_Port_Tbl is not yet set up. Initialize the console USART in a BSP_START system initialization handler and laizly on the first character. Provide BSP_poll_char for getchark().

Disabled STM32F4_ENABLE_USART_3 by default because not all stm32f4 boards have this port. Added PORT_COUNT \> 0 guards in case no USART is configured in config.ini.

Tested on STM32F411RE Nucleo board by running hello.exe

## AI Details

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### Prompt used

Not a single prompt, it was an iterative process.

### AI model used

Claude Opus 5.5

### How AI was used for the contribution

- [x] Formatting
- [ ] Test creation.
- [x] Code comments.
- [ ] The entire contribution was generated using AI
- [ ] AI code completion such as Copilot in VSCode.

If others were used please add below

The source of the crash was found by me with gdb, then I asked Calude for a fix, then I suggested changes to that solution.

### Access

I have not used a product which claims copyright in its output, and I have legitimate access to the one I used.

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View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1518
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