On Tuesday 09 December 2008 14:39, Bob Paddock wrote:
I had hoped that using OS_main would get rid of the call to main,
wastes stack space, and all of the dead _exit code, which is not allowed
under some design guidelines (as well as taking space), that will
never be executed, but it doesn't.
Is there an attribute that would?
I am aware of two solutions.
First, and most rigorous, is writing your own startup code and link with option
-nostartfiles. Please note this requires that you generate a vector table
yourself,
and has other drawbacks. (for example no .data section possible)
Second, and this trick works in some situations:
http://www.mail-archive.com/avr-gcc-list@nongnu.org/msg02390.html
For me the latter was not reliable enough, so i use the first option most of the
time. If you exactly know which interrupts to expect, you may even utilize
part of
the vector table for code.
But the most beautiful would be to have a compiler option like -embedded
or so, which gets rid of all junk.
I would be more that happy to hear how others solved this.
Below three examples (gcc 4.3.2 with patches):
1) Standard compile
2) Overwriting __methodes (Bjoern's trick)
3) with -nostartfiles + custom startup code
Note that, since the data section was empty in this example the
whole data copy loop is wasted space two.
Btw, if you compile with -Wno-main then you can use:
void main(void) __attribute__ (( OS_main ))
which reduces code somewhat more
1) Standard compile ===
__vectors:
0: 12 c0 rjmp.+36; 0x26 __ctors_end
2: 2c c0 rjmp.+88; 0x5c __bad_interrupt
4: 2b c0 rjmp.+86; 0x5c __bad_interrupt
6: 2a c0 rjmp.+84; 0x5c __bad_interrupt
8: 29 c0 rjmp.+82; 0x5c __bad_interrupt
a: 28 c0 rjmp.+80; 0x5c __bad_interrupt
c: 27 c0 rjmp.+78; 0x5c __bad_interrupt
e: 26 c0 rjmp.+76; 0x5c __bad_interrupt
10: 25 c0 rjmp.+74; 0x5c __bad_interrupt
12: 24 c0 rjmp.+72; 0x5c __bad_interrupt
14: 23 c0 rjmp.+70; 0x5c __bad_interrupt
16: 22 c0 rjmp.+68; 0x5c __bad_interrupt
18: 21 c0 rjmp.+66; 0x5c __bad_interrupt
1a: 20 c0 rjmp.+64; 0x5c __bad_interrupt
1c: df c0 rjmp.+446 ; 0x1dc __vector_14
1e: 1e c0 rjmp.+60; 0x5c __bad_interrupt
20: 1d c0 rjmp.+58; 0x5c __bad_interrupt
22: 1c c0 rjmp.+56; 0x5c __bad_interrupt
24: 1b c0 rjmp.+54; 0x5c __bad_interrupt
0026 __ctors_end:
26: 11 24 eor r1, r1
28: 1f be out 0x3f, r1; 63
2a: cf e6 ldi r28, 0x6F ; 111
2c: d0 e0 ldi r29, 0x00 ; 0
2e: de bf out 0x3e, r29 ; 62
30: cd bf out 0x3d, r28 ; 61
0032 __do_copy_data:
32: 10 e0 ldi r17, 0x00 ; 0
34: a0 e6 ldi r26, 0x60 ; 96
36: b0 e0 ldi r27, 0x00 ; 0
38: e8 e3 ldi r30, 0x38 ; 56
3a: f2 e0 ldi r31, 0x02 ; 2
3c: 02 c0 rjmp.+4 ; 0x42 .do_copy_data_start
003e .do_copy_data_loop:
3e: 05 90 lpm r0, Z+
40: 0d 92 st X+, r0
0042 .do_copy_data_start:
42: a0 36 cpi r26, 0x60 ; 96
44: b1 07 cpc r27, r17
46: d9 f7 brne.-10; 0x3e __SP_H__
0048 __do_clear_bss:
48: 10 e0 ldi r17, 0x00 ; 0
4a: a0 e6 ldi r26, 0x60 ; 96
4c: b0 e0 ldi r27, 0x00 ; 0
4e: 01 c0 rjmp.+2 ; 0x52 .do_clear_bss_start
0050 .do_clear_bss_loop:
50: 1d 92 st X+, r1
0052 .do_clear_bss_start:
52: a3 37 cpi r26, 0x73 ; 115
54: b1 07 cpc r27, r17
56: e1 f7 brne.-8 ; 0x50 .do_clear_bss_loop
58: 5c d0 rcall .+184 ; 0x112 main
5a: ec c0 rjmp.+472 ; 0x234 _exit
0112 main:
112: 0a d0 rcall .+20; 0x128 portInit
0234 _exit:
234: f8 94 cli
0236 __stop_program:
236: ff cf rjmp.-2 ; 0x236 __stop_program
2) Overwriting __methodes (Bjoern's trick)
__vectors:
0: 12 c0 rjmp.+36; 0x26 __ctors_end
2: 26 c0 rjmp.+76; 0x50 __bad_interrupt
4: 25
