> If you give me more information about what you are seeing (perhaps send me
> the code and how you are invoking the toolchain) I'll see what I can figure
> out.
Sure. I got sucked into a conversation on comparative microcontroller
architectures, and have been providing sample code produced by various PIC
compilers, avr-gcc, and I wanted to add msp430 to the conversation. I happen
to have a simple program that works pretty well as an example, except I don't
understand the code produced when I add optimization.
I'm using "msp430-gcc -mcpu=430 -Os -c flames.c" (various substitutes for -Os;
all but -O0 seem to have the same weird code.) I've attached the full program,
but the part in question is:
led_all_on();
for (pwm_delay = 128; pwm_delay !=0; pwm_delay--) {
/*
* We have a random number in each PWM between 1 and 128
* and we're going to have 128 cycles of delay. So each
* decremented output can only cross zero once, at which
* time we toggle the output state.
*/
if (--pwm1 == 0) {
led1_off;
}
if (--pwm2 == 0) {
led2_off;
}
if (--pwm3 == 0) {
led3_off;
}
Which produces:
38: b0 12 00 00 call #0x0000 ;; call to all_led_on()
3c: 45 4b mov.b r11, r5
3e: 75 50 80 ff add.b #-128, r5 ;; WTF? 1
42: 46 8b sub.b r11, r6 ;; ...
44: 47 8b sub.b r11, r7 ;; ...
46: 48 8b sub.b r11, r8 ;; ...
48: 49 8b sub.b r11, r9 ;; ...
4a: 7b 53 add.b #-1, r11 ;r3 As==11 ;; makes sense if
pwm1 is in r11.
4c: 02 20 jnz $+6
4e: b0 12 00 00 call #0x0000 ;; call to led1_off
52: 4f 46 mov.b r6, r15
54: 4f 5b add.b r11, r15 ;; WTF? 2? It thinks r11 has
-1? How? Why?
56: 02 20 jnz $+6
58: b0 12 00 00 call #0x0000 ;; call to led2_off
5c: 4f 47 mov.b r7, r15
5e: 4f 5b add.b r11, r15
60: 02 20 jnz $+6
62: b0 12 00 00 call #0x0000 ;; call to led3_off
The unoptimized code looks fine, if … unoptimized (size/speed wise, anyway):
5a: b0 12 00 00 call #0x0000 ;; call to all_led_on()
5e: f4 40 80 ff mov.b #-128, -4(r4)
62: fc ff
64: 25 3c jmp $+76
66: f4 53 f6 ff add.b #-1, -10(r4) ;; add to stack variable
6a: c4 93 f6 ff tst.b -10(r4) ;0xfff6(r4) ;; check for zero
(unneeded.)
6e: 02 20 jnz $+6
70: b0 12 00 00 call #0x0000
74: f4 53 f7 ff add.b #-1, -9(r4)
78: c4 93 f7 ff tst.b -9(r4)
7c: 02 20 jnz $+6
7e: b0 12 00 00 call #0x0000
82: f4 53 f8 ff add.b #-1, -8(r4)
86: c4 93 f8 ff tst.b -8(r4)
8a: 02 20 jnz $+6
8c: b0 12 00 00 call #0x0000
I'd expect to see something like:
call all_led_on
mov.b 128, r5 ;; loop counter
add.b #-1, r6 ;; pwm1 in register
jnz $+6
call led1_off
add.b #-1, r7 ;; pwm2 in register
jnz $+6
call led2_off
;; etc
------------------------------------------------------------------------------
Own the Future-Intel® Level Up Game Demo Contest 2013
Rise to greatness in Intel's independent game demo contest.
Compete for recognition, cash, and the chance to get your game
on Steam. $5K grand prize plus 10 genre and skill prizes.
Submit your demo by 6/6/13. http://p.sf.net/sfu/intel_levelupd2d
_______________________________________________
Mspgcc-users mailing list
Mspgcc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/mspgcc-users
