Initial commit - USE AT YOUR OWN RISK!
Built and tested for STM32F103CB (blue pill board), but should work on just about any platform.
Just include the following line:
#include <LibC.h>
in your main .ino file.
If you wish to use a static heap allocation for dynamic memory, then include the following too:
#define LIBC_HEAP_SIZE 10000 // 10,000 byte heap
#include <LibC_heap.h>
If you wish to remove float support from the printf library (~1k) then include the following lines in your main .ino file:
#define LIBC_PRINTF_NOFLOAT
#include <LibC_printf.h>
Since main() cannot exit in Arduino, replace all the following libc symbols with dummies:
- atexit
- __cxa_atexit
- exit
Saves a bit of code and RAM space in many situations.
NOTE: It is technically possible to declare a class destructor in a static class. If you explicitly call exit() then this destructor would normally be called before stopping the CPU. This will not happen anymore with this library - the CPU will stop immediately. (This is the same functionality as the AVR Arduino cores, so should not be an issue.)
Replace all the malloc/free family of functions with my own implementation.
Implementation priorities:
- Compact memory use
- Reduce fragmentation
- Small code
- Efficient code
So it is slow, and should not be used if you rely on rapid and frequent dynamic memory allocations.
New symbol:
void * crealloc(void *)
This reallocates the same size data (freeing the old, if moved). It is guaranteed not to fail, so it will always return an address, and that new addresss must always be used to access the data. This is used to 'bubble down' allocations, so that allocated data moves down whereever possible, and free space moves up/aggregates. Call this frequently on persistent allocations, where practical, and it will reduce memory fragmentation.
eg:
ptr = crealloc(ptr);
Will update ptr to the lowest available position in the heap, preserving data and size.
Replaced symbols:
- realloc
- malloc
- free
- calloc
- malloc_usable_size
- reallocarray (NOTE: equivallent to realloc - does NOT check size overflow!!)
The following symbols are not implemented and are replaced with functions which produce an instant memory fault:
- posix_memalign
- aligned_alloc
- valloc
- memalign
- pvalloc
Replace all printf/sprintf functions with my own implementation. Primary target is minimum flash usage with a full C feature set.
Usage:
Two APIs:
New function pprinf which takes any Print class as a first parameter.
pprintf(Serial, "Use Serial explicitly as a print device...\n");
Normal printf with a function to set which Print class will receive the output.
printf_setprint(&Serial); printf("Use Serial by setting it as the system print device...\n");
Replaced symbols:
- printf
- puts
- sprintf
- snprintf
- vprintf
- vsprintf
- vsnprintf
New symbols:
void printf_setprint(Print * p);
Designate an initialised Print class (eg Serial, GFX, Wire, etc) as the target for printf and vprintf calls.
int pprintf(Print& p, const char *format, ...);
As for fprintf, but the first argument is an initialised Print class.
Implementation is fairly complete, and if used exclusively is substantially cheaper in flash and stack than the Print class functions, while still providing substantial formatting capabilities.
Primary restrictions:
- only supports 32bit types (64bit ints, and doubles are cast down to 32/float)
- floats are calculated in place back to decimal representation - precision suffers after 8 significant digits
- 'a' format is functional, but formatting is not complete - not compiled by default
- m$ width and precision formats are not handled and treated as unset
- width is limited to 255 and precision 254
- 'g' my interpretation of precision differs from libc - mine as correct as I interpret the spec