microlog

Ultra-lightweight C logging for embedded systems

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microlog is a tiny, portable C logging library for STM32, ESP32, and any other embedded target. Drop in two files, set a macro, and get level-filtered, colour-coded logs over UART, RTT, or your own output channel.

Features

• Six levels: TRACE · DEBUG · INFO · WARN · ERROR · FATAL
• Zero-cost filtering: unneeded levels are compiled away to nothing
• Runtime level control via microlog_set_level()
• Optional ANSI colours make terminal logs readable at a glance
• Optional timestamp (any free-running tick, e.g. uwTick or esp_timer_get_time)
• File + line tracking
• Custom output — swap in your own UART/SWO/RTT function
• No malloc, no static buffers, no external dependencies
• C99 — works with GCC, ARMCC, IAR, Clang

Quick start

#define MICROLOG_IMPL
#define MICROLOG_COLOR 1
#define MICROLOG_LEVEL MICROLOG_DEBUG
#include "microlog.h"

int main(void) {
    log_info("System booted");
    log_warn("Voltage dropped to %d mV", 3100);
    log_error("I2C timeout on bus %d", 2);
    return 0;
}

Build & run on desktop:

gcc -I. -DMICROLOG_COLOR=1 -DMICROLOG_LEVEL=0 examples/pc_example.c -o pc_example
./pc_example

Integration

Platform	How-to
STM32 + HAL	Provide MICROLOG_OUTPUT_FN → wrap HAL_UART_Transmit. See examples/stm32_example.c
ESP32 + ESP-IDF	Provide MICROLOG_OUTPUT_FN → call esp_rom_printf. See examples/esp32_example.c
Desktop / testing	Use the built-in puts(); nothing to wire. See examples/pc_example.c

API

/* Level constants */
MICROLOG_TRACE  0
MICROLOG_DEBUG  1
MICROLOG_INFO   2
MICROLOG_WARN   3
MICROLOG_ERROR  4
MICROLOG_FATAL  5

/* Macros (compile-time filtered by MICROLOG_LEVEL) */
log_trace(...)
log_debug(...)
log_info(...)
log_warn(...)
log_error(...)
log_fatal(...)

/* Runtime control */
void microlog_set_level(int level);
int  microlog_get_level(void);

Config macros

Define these before including the header to tailor the library:

Macro	Default	Effect
MICROLOG_LEVEL	MICROLOG_INFO	Minimum level compiled in
MICROLOG_COLOR	0	Enable ANSI colour output
MICROLOG_TICK_FN	unset	uint32_t fn(void) returning a millisecond tick
MICROLOG_OUTPUT_FN	puts	User's output function void fn(const char *s)
MICROLOG_DISABLE	0	Set to 1 to remove all log code entirely

Project structure

microlog/
├── microlog.h             API + implementation (define MICROLOG_IMPL once)
├── README.md
├── LICENSE                MIT
└── examples/
    ├── pc_example.c        desktop demo
    ├── stm32_example.c     STM32 + HAL_UART
    └── esp32_example.c     ESP-IDF

License

MIT