Minimal printf() implementation for embedded projects.

I was recently working on an embedded project with a STM32 MCU. The chip had 32kB of flash memory - that's heaps for a microcontroller! How surprised I was when the linker suddelnly failed saying that the program is too big and won't fit! How come?!

It's just some USB, I2C, GPIO, a few timers ... and snprintf() It turned out the memory hog was indeed the glibc's snprintf() - it took nearly 24kB out of my 32kB and left very little for my program.

Now what? I looked around the internet for some stripped down printf() implementations but none I really liked. Then I decided to develop my own minimal snprintf().

Here are some numbers (.bin file size of my STM32 project):

no snprintf():      10768 bytes
mini snprintf():    11420 bytes     (+  652 bytes)
glibc snprintf():   34860 bytes     (+24092 bytes!!)

Why snprintf() and not printf()? Simply because there are so many different ways to print from an embedded system that I can't really make an universal-enough printf().

The way I chose makes printing really easy - use mini_snprintf() to print into a "char buffer[]" and then output that buffer to your chip's USART, USB or network or whatever other channel you fancy.

As a by-product there's also a mini_vsnprintf() function available.

I didn't implement each and every formatting sequence the glibc does. For now only these are supported:

%%       - print '%'
%c       - character
%s       - string
%d, %u   - decimal integer
%x, %X   - hex integer

The integer formatting also supports 0-padding up to 9 characters wide. (no space-padding or left-aligned padding yet).

The implementation should be compatible with any GCC-based compiler. Tested with native x86-64 gcc, arm-none-eabi-gcc and avr-gcc.

It's completely standalone without any external dependencies.

1. Include "mini-printf.h" into your source files.
2. Add mini-printf.o to your objects list.
3. Use snprintf() as usual in your project.
4. Compile, Flash, Test

Written by: Michal Ludvig [email protected]

Project homepage: http://logix.cz/michal/devel/mini-printf

Source download: https://github.com/mludvig/mini-printf

Donations: http://logix.cz/michal/devel/donations

Copyright (c) 2013,2014 Michal Ludvig [email protected] All rights reserved.

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