crt1 for BrailleBuzz (STM32F103) January 29, 2015

crt1

This is the low level operating system type stuff. Well, we don’t have one, but we’d still like things like printf and malloc to work or at least not crash. Remember after you call printf, somewhere down the pike some ascii (or unicode) has to go somewhere. In our case we’re going to output it to one of the UARTs. This is very convenient when debugging! This code took a long time to sort out and is incomplete. I got some of the stubs from the manufacturer. Recall that in a unix OS we would be opening files (in dev), reading from and writing to them but here we don’t have an OS or a file-system so we make some assumptions, lots of assumptions.

crt1.h

#ifndef __CRT1_H__
#define __CRT1_H__

void _init_crt1();

#endif /* __CRT1_H__ */

crt1.c

#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <sys/stat.h>
#include "stm32f10x_usart.h"

#include "irq.h"

extern int8_t _sheap;
extern int8_t _eheap;
static const int8_t* eheap_p = &_eheap;
static const int8_t* sheap_p = &_sheap;
static intptr_t heap_ptr;

size_t heap_peak = 0x0;

long _write_r(struct _reent *_r, int fd, const void *buf, int cnt)
{
    int n;
    const char *ptr = buf;
    for (n = 0; n < cnt; n++) {

        while ((USART2->SR & USART_FLAG_TC) == 0x0000);
        USART2->DR = (*ptr++ & 0x01FF);

    }
    return cnt;
}

long _read_r(struct _reent *_r, int fd, char *ptr, int len )
{
        while ((USART2->SR & USART_FLAG_RXNE) == 0x0000);
        *ptr = (char) (USART2->DR & 0x01FF);
  return 1;
}

off_t _lseek_r( struct _reent *_r, int fd, off_t pos, int whence )
{
   return 0;
}

int _isatty( struct _reent *_r, int fd)
{
  return 1;
}

int _fstat_r ( struct _reent *_r, int fd, struct stat *pstat)
{
   pstat->st_mode = S_IFCHR;
   return 0;
}

long _close_r(struct _reent *_r, int fd)
{
  _r->_errno = EBADF;
  return -1;
}

/*
int _open_r (struct _reent *_r, const char *file, int flags, int mode)
{ 
  _r->_errno = ENODEV;
  return -1;
}
*/


void *_sbrk_r(struct _reent *r, intptr_t incr)
{
  void* retval = 0;
  intptr_t newbrk = (intptr_t)((size_t)heap_ptr + (size_t)incr);

  if(newbrk >=  (intptr_t)eheap_p)
    {
      r->_errno = ENOMEM;
      retval = (void *)-1;
    }
  else 
    {
      const size_t new_size = ((size_t)newbrk) - ((size_t)sheap_p);
      heap_peak = (heap_peak < new_size) ? new_size : heap_peak;
      retval = (void*)heap_ptr;
      heap_ptr = newbrk;

    }

  return  retval;
}

void _init_crt1() 
{
  /* set the heap with 0xff */
  {
    const size_t heapsize = ((size_t)(eheap_p)) - ((size_t)sheap_p);
    memset(&_sheap, 0xff, heapsize);
    heap_ptr = (const intptr_t)sheap_p;
  }
}

void _exit(int i) {
    while(1);

}