Logger System Usage Guide

This document explains how to use the modular logging system (logger.h / logger.c) designed for STM32 MCU projects with UART and SD card output.

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Features

• UART output with blocking, interrupt (IT), or DMA modes
• Optional SD card logging (FatFS required)
• Ring buffer for non-blocking UART output
• Runtime log level filtering (ERROR, WARN, INFO, DEBUG)
• Logging disable and flush support
• Easy to override hooks for custom output targets

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Files

• logger.h – Public interface and configuration
• logger.c – Implementation with ring buffer, UART/SD output, and FatFS integration

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Configuration

Set these macros before including logger.h or define them in a logger_config.h (optional).

#define LOG_USE_UART 1       // Enable UART output (default 1)
#define LOG_USE_SD   1       // Enable SD card logging (default 0)
#define LOG_USE_IT   1       // Use UART interrupt (default 1)
#define LOG_USE_DMA  0       // Use UART DMA instead of IT (default 0)
#define LOG_BUFFER_SIZE 256  // printf-style buffer size
#define LOG_RING_BUFFER_SIZE 1024  // UART TX buffer size

Only one of LOG_USE_DMA or LOG_USE_IT should be enabled.

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Initialization and Usage

Initialization:

#include "logger.h"
 
Log_Init();                // Initialize ring buffer and SD card file
Log_SetLevel(LOG_LEVEL_DEBUG);  // Set desired verbosity level

Logging:

Log(LOG_LEVEL_INFO, "Startup complete\n");
Log(LOG_LEVEL_DEBUG, "Sensor: %f\n", temperature);

Disabling/Flushing:

Log_Disable();             // Disable logging (run-time)
Log_Flush();               // Sync SD card log file

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UART Integration

You must define a UART handle externally:

extern UART_HandleTypeDef huart1;

And call the UART complete callback:

void HAL_UART_TxCpltCallback(UART_HandleTypeDef *huart) {
    // Call into logger
    Logger_HAL_UART_TxCpltCallback(huart); // or place `ring_buffer_send_next()` inline
}

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SD Card Integration

Requires:

• FatFS (ff.h) and disk I/O working
• Mount must be done before Log_Init()
• Writes to log.txt in append mode

Auto flushes on Log_Flush() using f_sync():

f_open(&log_file, "log.txt", FA_OPEN_ALWAYS | FA_WRITE);
f_lseek(&log_file, f_size(&log_file));
f_write(&log_file, msg, strlen(msg), &bw);
f_sync(&log_file);

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Custom Output Hooks

You can override either of these functions to customize output:

__attribute__((weak)) void Log_Write_UART(const char* msg);
__attribute__((weak)) void Log_Write_SD(const char* msg);

For example, redirect output to USB or a BLE service.

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Example Session

Log_Init();
Log_SetLevel(LOG_LEVEL_INFO);
 
Log(LOG_LEVEL_INFO, "System booting\n");
Log(LOG_LEVEL_DEBUG, "Debug info will not show at this level\n");
 
Log_SetLevel(LOG_LEVEL_DEBUG);
Log(LOG_LEVEL_DEBUG, "Now debug logs will show\n");
 
Log_Disable();
Log(LOG_LEVEL_ERROR, "This will not be printed\n");
 
Log_Flush(); // Save data to SD

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Tips

• You can queue logs during runtime with LOG_USE_IT or LOG_USE_DMA
• For CLI coexistence, use a shared ring buffer or alternate UARTs
• For safety, call Log_Flush() before shutting down or resetting the MCU

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