MAX32655 UART fails to send some bytes on Zephyr 4.3 #103365

Describe the bug

As fixed in #99308, on MAX32 the "Transmit FIFO Almost Empty" interrupt is used to check for completion of a TX, but when a transfer of just one byte is initiated, the interrupt will never fire, leading to a "hang" in the serial logic that is waiting for a TX to complete before sending more.

When using the shell sample, for instance, this will manifest as shell output that suddenly stops without sending the next shell prompt. Pressing a key will raise an RX that will then trigger the TX to be detected as completed.

This may of course manifest in other ways, but the shell example is the most direct way to reproduce.

Regression

• This is a regression.

Steps to reproduce

1. Build the shell sample for a MAX32655 feather board: west build -p -b max32655fthr//m4 samples/subsys/shell/shell_module and flash to a board
2. Connect to the console with your serial tool of choice.
3. Interact with the shell, even hitting enter at an empty prompt can trigger the bug.
4. Wait for an enter press to be received, but no new shell prompt is printed on the console

Relevant log output

Impact

Functional Limitation – Some features not working as expected, but system usable.

Environment

No response

Additional Context

No response