3.17.2 Stdclib functions (puts, printf, strcat etc.)

3.17.2.1 <stdio.h>

3.17.2.1.1 getchar(), putchar()

As usual on embedded systems you have to provide your own getchar() and putchar() routines. SDCC does not know whether the system connects to a serial line with or without handshake, LCD, keyboard or other device. And whether a lf to crlf conversion within putchar() is intended. You'll find examples for serial routines f.e. in sdcc/device/lib. For the mcs51 this minimalistic polling putchar() routine might be a start:

void putchar (char c) {  
    while (!TI)    /* assumes UART is initialized */ 
        ; 
    TI = 0; 
    SBUF = c; 
}

3.17.2.1.2 printf()

The default printf() implementation in printf_large.c does not support float (except on ds390). To enable this recompile it with the option -DUSE_FLOATS=1 on the command line. Use --model-large for the mcs51 port, since this uses a lot of memory.

If you're short on code memory you might want to use printf_small() instead of printf(). For the mcs51 there additionally are assembly versions printf_tiny() (subset of printf using less than 270 bytes) and printf_fast() and printf_fast_f() (floating-point aware version of printf_fast) which should fit the requirements of many embedded systems (printf_fast() can be customized by unsetting #defines to not support long variables and field widths). Be sure to use only one of these printf options within a project.

Feature matrix of different printf options on mcs51.

mcs51	printf	printf USE_FLOATS=1	printf_small	printf_fast	printf_fast_f	printf_tiny
filename	printf_large.c	printf_large.c	printfl.c	printf_fast.c	printf_fast_f.c	printf_tiny.c
''Hello World'' size small / large	1.7k / 2.4k	4.3k / 5.6k	1.2k / 1.8k	1.3k / 1.3k	1.9k / 1.9k	0.44k / 0.44k
code size small / large	1.4k / 2.0k	2.8k / 3.7k	0.45k / 0.47k (+ _ltoa)	1.2k / 1.2k	1.6k / 1.6k	0.26k / 0.26k
formats	cdiopsux	cdfiopsux	cdosx	cdsux	cdfsux	cdsux
long (32 bit) support	x	x	x	x	x	-
byte arguments on stack	b	b	-	-	-	-
float format	-	%f	-	-	%f3.9	-
float formats %e %g	-	-	-	-	-	-
field width	x	x	-	x	x	-
string speed3.10, small / large	1.52 / 2.59 ms	1.53 / 2.62 ms	0.92 / 0.93 ms	0.45 / 0.45 ms	0.46 / 0.46 ms	0.45 / 0.45 ms
int speed3.11, small / large	3.01 / 3.61 ms	3.01 / 3.61 ms	3.51 / 18.13 ms	0.22 / 0.22 ms	0.23 / 0.23 ms	0.25 / 0.25 ms3.12
long speed3.13, small / large	5.37 / 6.31 ms	5.37 / 6.31 ms	8.71 / 40.65 ms	0.40 / 0.40 ms	0.40 / 0.40 ms	-
float speed3.14, small / large	-	7.49 / 22.47 ms	-	-	1.04 / 1.04 ms	-

3.17.2.2 <malloc.h>

As of SDCC 2.6.2 you no longer need to call an initialization routine before using dynamic memory allocation and a default heap space of 1024 bytes is provided for malloc to allocate memory from. If you need a different heap size you need to recompile _heap.c with the required size defined in HEAP_SIZE. It is recommended to make a copy of this file into your project directory and compile it there with:

sdcc -c _heap.c -D HEAD_SIZE=2048

And then link it with:

sdcc main.rel _heap.rel