Assembler in Cosmic C compiler

[bleumers_j]

Posted on November 06, 2003 at 09:17

Assembler in Cosmic C compiler

[bleumers_j]

Posted on June 18, 2003 at 08:29

Hello everyone,

I want to write a small part of the code of my program in assembler, the rest is written in C. Doing this is no problem in Cosmic, but...

The assembler part writes data into a variable that is used in the C code.

How can i manage that C an assembler use the same memory place for this variable?

Thanks...

[parveen]

Posted on June 18, 2003 at 10:45

You can do this by two methods:

1)Use absolute addressing for declaring variables

volatile unsigned char i @0x80;

Above instruction will declare i at memory lacation 0x80 and in your assembly you can use this address

2) use _asm function

_asm(''SRA A\n LD $80,a\n'',j);

This instruction will load variable j in A and shift it right, next it will load the result in A at 0x80

Hope this helps

Regards,

PraveenG

[ This message was edited by: praveenG on 18-06-2003 15:15 ]

[sjo]

Posted on June 18, 2003 at 12:04

The correct way would be:

unsigned char data; // c variable

void somefunc(void)

{

#asm

ld a, #10

ld _data, a

#endasm

}

If the variables are declared in another file then use the XREF keyword,eg.

#pragma asm

xref _data

#pragma endasm

Regards

Spen

[bleumers_j]

Posted on June 18, 2003 at 12:04

Hi,

I've tried this :

int waarde;

void main(){

#asm

LD A, #100

LD _waarde,A

#endasm

schrijfPWM(3,waarde);

}

but it didn't work, anyone an idea what i did wrong??? When i write ex. '' waarde = 255;'' it works fine, so ''schrijfPWM()'' works well.

thanks.

[ This message was edited by: joble on 18-06-2003 15:51 ]

[bleumers_j]

Posted on June 18, 2003 at 12:41

Hi again,

Finally it works!

The variable should be a char (like in the example sjo gave) instead of an int. I do not understand why, but it seems to be that way...

Thanks both for your help!

[sjo]

Posted on June 18, 2003 at 13:39

If you need to use an int, then remenber you have to work on both chars, eg.

int data;

void somefunc(void)

{

#asm

ld a, #10

ld _data, a ; msb of int

clr _data+1 ; lsb of int

#endasm

}

Regards

Spen

[stephen239955_stm1]

Posted on November 06, 2003 at 07:57

Quote:

How about declaring the variable ''data'' in somefunc() as a local variable?

I tried. But it didn't work and showed _data undefined.

I can't find the helpful information in documentation.

Thanks a million!

slin

[sjo]

Posted on November 06, 2003 at 09:17

This is not possible on local variables because of the way the compiler treats locals, eg.

Depending on memory model, options etc a variable declared locally such as:

unsigned char var

is actually internal as _main$L-1. (using memory stack)

Have a look inside the listing file to see what I mean.

Regards

sjo