Hi
I have the following code segment whose purpose is to toggle an LED every time
the
watchdog timer interrupt occurs:
interrupt(WDT_VECTOR) WatchdogHandler(void)
{
static char st = 0;
IFG1 &= ~WDTIFG;
if (st)
{
LED1_ON();
}
else
{
LED1_OFF();
}
st = !st;
IE1 = (IE1 | WDTIE);
}
The problem I am seeing is that the static 'st' variable is not being inverted
correctly.
The assembler code produced with -01 is:
71:watchdog.c **** st = !st;
140 .stabn 68,0,71,.LM11-WatchdogHandler
141 .LM11:
142 0028 5C42 0000 mov.b &st.0, r12
143 002c 4C93 tst.b r12
144 002e 0234 jge .Leaq33
145 0030 7CE3 inv.b r12
146 0032 5C53 inc.b r12
147 .Leaq33:
148 0034 7C53 add.b #llo(-1), r12
149 0036 4C11 rra.b r12
150 0038 4C43 clr.b r12
151 003a 4C10 rrc.b r12
152 003c C24C 0000 mov.b r12, &st.0
If I watch the memory location where 'st' is stored (it is 0x200 on my app, I
checked by
disassembling the output ELF file) I can see that it gets inverted correctly
from 0x00 to
0x80 the first time around the loop but then is always left at 0x80 and never
inverted
again to 0x00. If I write the above explicitly ie.
if (st)
st = 0;
else
st = 1 (or 0x80, whatever as long as it isn't 0x00)
my handler behaves as expected ie. the LED is toggled.
If I build the same code with -O0 (optimisations off) I get this:
149 .stabn 68,0,71,.LM11-WatchdogHandler
150 .LM11:
151 0036 C143 0200 mov.b #llo(0), 2(r1)
152 003a C293 0000 tst.b &st.0
153 003e 0220 jne .L5
154 0040 D143 0200 mov.b #llo(1), 2(r1)
155 .L5:
156 0044 D241 0200 mov.b 2(r1), &st.0
which is a lot more compact and works correctly !
I am using a MSP430F149 and a fairly (a week or two old) build of the
MSP430GCC.
Any comments ? What command line options do people typically use with
msp430-gcc
ie. in terms of optimisations, etc. I guess for now I will use -O0
Regards.
Colin
---------------------------------------------------------------------------------
Colin Domoney
Digital Hardware Design Engineer
NCipher, Jupiter House, Station Road, Cambridge, CB1 2JD
e-mail: [email protected]
Telephone: +44-1223-723630
