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Assembly

Started by Tiger99 Mar 10, 2003 at 8:58 PM 4 replies 250+ views

Original Post

Mar 10, 2003 at 8:58 PM

Hello I am not familiar with assembly language. Can someone please explain what the following inline assembly is doing VOID rtx_dbug_out_char( CHAR c ) { asm( "sub.l #60, %a7" ); asm( "movem.l %d0-%d7/%a0-%a6, (%a7)" ); asm( "move.l 8(%a6), %d1" ); asm( "move.l #0x13, %d0" ); asm( "trap #15" ); asm( "movem.l (%a7), %d0-%d7/%a0-%a6" ); asm( "add.l #60, %a7" ); } I am trying to build a simple real time OS. I need to allocate memory for all the OS processes. Should I do the allocation in C or assembly? Some sample code will be helpful Thanks in advance

Nypyren

1,001

Nypyren

Mar 10, 2003 at 10:48 PM

OMFG! I don''t know that form of assembly syntax... and I know AT&T and Intel syntax...

Tiger99

Author

Tiger99

Mar 10, 2003 at 11:35 PM

Come on, someone here must know assembly language for ColdFire board

Any help will be very appreciated

ThoughtCriminal

Mar 11, 2003 at 3:11 AM

quote:
Original post by Tiger99
Hello
I am not familiar with assembly language. Can someone please explain what the following inline assembly is doing

VOID rtx_dbug_out_char( CHAR c )
{

asm( "sub.l #60, %a7" );
^^^making space on the stack
asm( "movem.l %d0-%d7/%a0-%a6, (%a7)" );
^^^move multiple regs on the stack(store all regs on stack)
asm( "move.l 8(%a6), %d1" );
^^^move dword value at A6+8 to data reg D1
asm( "move.l #0x13, %d0" );
^^^move immediate hex val 13h to data reg D0
asm( "trap #15" );
^^^trap is like an x86 int
asm( "movem.l (%a7), %d0-%d7/%a0-%a6" );
^^^move multiple from stack to regs(restore regs)
asm( "add.l #60, %a7" );
^^^fix stack(balance stack)
}

I am trying to build a simple real time OS. I need to allocate memory for all the OS processes. Should I do the allocation in C or assembly? Some sample code will be helpful

Thanks in advance

It looks like 68k code. Look for some docs for trap #15 function 13h to tell what it does. Guessing buy the function name, I'd say it will out put the character at address reg A6+8 to the terminal.

[edited by - ThoughtCriminal on March 11, 2003 4:13:37 AM]

tok_junior

Mar 11, 2003 at 3:23 AM

It''s most certainly motorola code, i''m not so sure it''s for the 68k line though...
What is your target architecture?

--
MFC is sorta like the swedish police... It''''s full of crap, and nothing can communicate with anything else.

Sneftel

296

Sneftel

Mar 11, 2003 at 3:40 AM

it certainly looks 68k from here; what it is doing is saving all variables onto the stack, then setting registers D0 and D1 (D0 it initializes to the constant 0x13; D1 most likely refers to a local variable). Then it calls trap 15 (kind of like an int call under x86 assembly. When the trap returns, it restores all variables from the stack.

This is the sort of code one would use to access OS functions.

Edit: Okay, ThoughtCriminal's waaaay ahead of me here. Listen to him.

But... but that's what HITLER would say!!

[edited by - sneftel on March 11, 2003 4:41:56 AM]

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