Please see my note book http://mbed.org/users/kenjiArai/notebook/freertos-on-mbed-board-with-mbed-cloud-ide--never-/

This is too old.
Below is another FreeRTOS on mbed.
http://developer.mbed.org/users/rgrover1/code/FreeRTOS/
I don't know it works well or not.
I have not evaluated it.

syscalls.c

Committer:
kenjiArai
Date:
2011-01-01
Revision:
0:d4960fcea8ff

File content as of revision 0:d4960fcea8ff:

/* Don't need anything here. */

#include <stdlib.h>
#if 0
#include <sys/stat.h>
#else

#endif

//---------------------------------
// from types.h
typedef    char *    caddr_t;
//----------------------------------

int _read_r (struct _reent *r, int file, char * ptr, int len)
{
    ( void ) r;
    ( void ) file;
    ( void ) ptr;
    ( void ) len;
    return -1;
}

/***************************************************************************/

int _lseek_r (struct _reent *r, int file, int ptr, int dir)
{
    ( void ) r;
    ( void ) file;
    ( void ) ptr;
    ( void ) dir;
    
    return 0;
}

/***************************************************************************/

int _write_r (struct _reent *r, int file, char * ptr, int len)
{  
    ( void ) r;
    ( void ) file;
    ( void ) ptr;
    ( void ) len;
    
    return 0;
}

/***************************************************************************/

int _close_r (struct _reent *r, int file)
{
    ( void ) r;
    ( void ) file;

    return 0;
}

/***************************************************************************/

caddr_t _sbrk_r (struct _reent *r, int incr)
{
    ( void ) r;
    ( void ) incr;
    
    return 0;
}

/***************************************************************************/

int _fstat_r (struct _reent *r, int file, struct stat * st)
{
    ( void ) r;
    ( void ) file;
    ( void ) st;
    
    return 0;
}

/***************************************************************************/

int _isatty_r(struct _reent *r, int fd)
{
    ( void ) r;
    ( void ) fd;
    
    return 0;
}