Hi,
> I am working on PCB tester with programming capabilities for PIC - of
> course in SDCC. I compile target.c, generated HEX is then processed into
> .H file and linked together with code of the main application. Target
> code is really simple, but it seems to me that overhead is quite big. I
> tried the simplest code with LED blinking and SW UART (see below).
>
> If I compile it, the main code itself has about 216bytes (taken from
> .LST). But when I link it, I get around 460 bytes. With
> "--use-crt=crt0.o" I get around 270 bytes, it is better.
>
> My questions are:
> - Why "vectors" page is 0x00-0x29 ? Where is said, how much memory I
> need for INT jumps ? I feel that 2 bytes are enough - just "goto
> __INT_HANDLER".
I do not know where this comes from, but it might be a joke: 0x2A equals
the famous 42 ... And no, 2 byte for the goto do not suffice: goto is
4 byte long. But 4 byte for the RESET vector should do fine iff you
do not use any interrupts. Do you really need the space for these < 20
instructions?!?
> - I understand that if I don't use any interrupt, I can reduce "vectors"
> page to 0x04, can't I ?
You probably can, no guarantees, though: I never did that myself.
> - When is it necessary to use "crt0i" instead of "crt0" ?
crt0i initializes your global and/or static variables. Whenever you have
int flag = 1; /* initialized global variable */
int flag2 = 0; /* initialized global variable */
int foo(void)
{
static int bar = 42; /* static variable */
int baz = 4; /* <-- not static, would not require crt0i.o */
}
you need crt0i.o. Beware: Even initializing to 0 requires
either crt0i.o (or crt0iz.o, which clears all uninitialized
memory) to guarantee correct initialization after reboot
(and even after initial boot iff your memory was not 0
before).
In short: if you rely on a paritcular memory cell having a
defined value after startup, you need crt0i.
> void swuart_del()
> {
> unsigned char icnt2;
> for( icnt2 = 0; icnt2 < 80; icnt2++) ;
> }
Consider using __asm __endasm; as the loop body,
otherwise the compiler optimize your precious delay
loop away.
Best regards,
Raphael
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