Use Cases

1. Application Logging Over UART

This use case illustrates printf-based application logging over UART. It requires:

  • UART interface configured for TX (baud rate, pins, instance).

  • Basic STDIO initialized with the selected UART interface.

  • A UART terminal or viewer connected to the target port.

@startuml title **Basic STDIO stdout redirection over UART** participant "User Application" as UA participant "libc" as libc participant "'Basic STDIO' utility" as UT_BS participant "'Basic STDIO' interface" as I_BS participant "HAL" as HAL group #LightYellow "Initialization" UA --> HAL : HAL_UART_Init(&USART1, HAL_UART1); UA --> UT_BS : BASIC_STDIO_Init(&USART1); UT_BS --> I_BS: interface_io_Init(&USART1); end group #LightBlue "Process: infinite loop" UA --> libc : printf("This is a log message"); alt GCC (_write) libc --> UT_BS : _write(stdout, "This is a log message") else IAR (__write) libc --> UT_BS : __write(stdout, "This is a log message") else Others: armclang, older runtimes (fputc) libc --> UT_BS : fputc(c) note right of libc called once per character end note end UT_BS --> I_BS : interface_io_Send(puartObj,\n"This is a log message", 22); I_BS --> HAL : HAL_UART_Transmit(puartObj,\n"This is a log message", 22); end @enduml

This is useful for early board bring-up and lightweight runtime logging in the main loop.

2. Conditional Prints

This use case illustrates build-time conditional prints that keep or remove messages without modifying the application code. It requires:

  • A wrapper macro PRINTF(...) defined as below.

  • Build flag USE_TRACE=1 to enable, or USE_TRACE=0 to disable (calls are removed at preprocessing time and arguments are not evaluated).

  • Output interface configured and Basic STDIO initialized when enabled.

Example: 

/* Conditional print macro.
 * Enable with USE_TRACE=1.
 * When disabled (USE_TRACE undefined or 0), no code is generated.
 */
#if defined(USE_TRACE) && (USE_TRACE != 0)
#define PRINTF(...) printf(__VA_ARGS__)
#else
#define PRINTF(...)
#endif

This use case helps remove all runtime prints in production builds, skip argument evaluation (for better performance), reduce the flash footprint, and keep the original source readable without modifications.