Re: [Sdcc-user] interrupt routines

[Olgierd E. <ol...@te...>]

Ok, then the problem was not to link with the crtX0.o file, I didn't
know about what the crt0 files were for, it's not in the manual. 

Thanks a lot

Olgierd

On Thu, 2006-04-27 at 02:11 +0300, Vangelis Rokas wrote:
> ----- Original Message ----- 
> From: "Olgierd Eysymontt" <ol...@te...>
> To: <sdc...@li...>
> Subject: Re: [Sdcc-user] interrupt routines
> 
> 
> >I don't fully understand how the indirect addressing is managed by SDCC,
> 
> The example you mention has nothing to do with indirect addressing! PIC16
> port uses FSR0 for indirect addressing while reserves FSR1 for stack pointer
> and FSR2 for frame pointer.
> 
> > I've made a small program that does nothing but calling a subroutine
> > that does nothing, but shows how the FSRx registers are uses, the code
> > is :
> >
> > <-- init stuff -->
> > void main() {
> > setup_ini();
> > while(1){
> > delay100ktcy(100);
> > }
> >
> > }
> >
> > void setup_ini(){
> > }
> >
> > The ASM generated by SDCC is :
> >
> > <--imported registers -->
> >
> > ;--------------------------------------------------------
> > ; public variables in this module
> > ;--------------------------------------------------------
> > global _addr
> > global _stack
> > global _stack_end
> > global _setup_ini
> > global _main
> > ;--------------------------------------------------------
> > ; Equates to used internal registers
> > ;--------------------------------------------------------
> > FSR1L equ 0xfe1
> > FSR2L equ 0xfd9
> > POSTDEC1 equ 0xfe5
> > PREINC1 equ 0xfe4
> >
> > udata_test_1_leds_0 udata
> > _addr res 1
> >
> >
> > ustat_test_1_leds_00 udata 0X0200
> > _stack res 99
> > _stack_end res 1
> >
> > ;--------------------------------------------------------
> > ; interrupt vector
> > ;--------------------------------------------------------
> >
> > ;--------------------------------------------------------
> > ; global & static initialisations
> > ;--------------------------------------------------------
> > ; I code from now on!
> > ; ; Starting pCode block
> > S_test_1_leds__main code
> > _main:
> > ; .line 36; test_1_leds.c setup_ini();
> > CALL _setup_ini
> > _00106_DS_:
> > ; .line 41; test_1_leds.c delay100ktcy(100);
> > MOVLW 0x64
> > CALL _delay100ktcy
> > GOTO _00106_DS_
> > RETURN
> >
> > ; ; Starting pCode block
> > S_test_1_leds__setup_ini code
> > _setup_ini:
> > ; .line 46; test_1_leds.c void setup_ini(){
> > MOVFF FSR2L, POSTDEC1
> > MOVFF FSR1L, FSR2L
> > ; .line 52; test_1_leds.c }
> > MOVFF PREINC1, FSR2L
> > RETURN
> >
> >
> >
> > ; Statistics:
> > ; code size:    30 (0x001e) bytes ( 0.02%)
> > ;              15 (0x000f) words
> > ; udata size:   101 (0x0065) bytes ( 2.74%)
> > ; access size:     0 (0x0000) bytes
> >
> >
> > end
> >
> 
> > My question is where are initialized the FSR2L (frame pointer) and other
> > FSRxx registers ?? because after a reset their content are unknown.
> 
> FSR1 and FSR2 are initialized in device/lib/pic16/startup/crt0*.o files.
> These hook the RESET vector so the gain control when the uC powers up,
> resets, etc...
> crt0.c simply initializes stack and frame pointer
> crt0i.c initializes stack/frame pointers and sets up variables with 
> initializers
> crt0iz.c is same as crt0i.c first it sets all RAM memory to zeroes (0)
> 
> 
> > I have another question, sorry for my ignorance, I've never programmed
> > ASM before, so what is the frame pointer used to ?
> 
> When passing variables to a function, these are stored temporarly on stack.
> Stack pointer after entering such a function might be further changed to 
> account
> for registers that are used locally in the function. So, there should be a 
> pointer to
> point at function arguments regardless the state of the stack pointer. See 
> hot more
> complex functions work and you'll understand the purpose of frame pointer.
> 
> Normally, in an empty function ( setup_ini() ) no FSR2 initialization code 
> should be
> emitted at all. Is setup_ini() really empty?
> 
> regards,
> Vangelis
> 
> 
> 
> 
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