Problem combining Assembly and C

A

avinsinanan

New Member

• Mar 20, 2003

• #1

Hello I am using TURBO C to read an input valuie from the Parallel Port.

I am putting Assembly language in Turbo C. However the printf statement is not printing the value in the regsiter. WHy?

Here is the code -

# include <stdio.h>
#define PORT_ADDRESS 0x379

void main()
{
for(int i=0;;i++)
{
asm {
MOV DX , 0379H
IN AX,DX
}
printf(DX);
}
}


Why isn't it working?

Thanks

 

kinjalgp

Active Member

• Mar 20, 2003

• #2

I think the last printf should be:
printf(AX);
Since IN instruction puts the value of port in accumulator.

You can also use InportB and OutportB functions defined in conio.h file.

 

P

Pilot

New Member

• Mar 22, 2003

• #3

Would it not be better to call printf() from within the asm block....

ie.

# include <stdio.h>
#define PORT_ADDRESS 0x379

void main()
{
for(int i=0;;i++)
{
asm {
MOV DX , 0379H
IN AX,DX
call printf();
}
}
}

I await instant correction from anyone - too many years since I did C - too much COBOL recently.

 

kinjalgp

Active Member

• Mar 22, 2003

• #4

There is no keyword called "call" in 'C'. And also you have not passed any parameter to printf() function. So it won't print anything.

 

P

Pilot

New Member

• Mar 22, 2003

• #5

Kinjalgp

I got it wrong.

I should not have included the brackets or semi-colon as that denotes a c function and I forgot to push AX.

Using the 8086 inline assembler the instruction call printf
is valid.

See the following example....

https://msdn.microsoft.com/library/...re_calling_c_functions_in_inline_assembly.asp

Like I said.. too many years away from C/assembler.