A89: Help with Link Routine

To: assembly-89@lists.ticalc.org
Subject: A89: Help with Link Routine
From: BLoWh0Le@aol.com
Date: Fri, 25 Dec 1998 00:32:03 EST
Delivered-To: assembly-89-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-89@lists.ticalc.org


I've cut a snippet of code from Tetris 89, which I'm guessing is the backbone
of the link routine.  I, however, don't fully understand it and would
appreciate some clarification.  Below is the code and what I think I know
about it.

SendByte:
 movem.l d0-d1/a0-a1,-(a7)		;saves the registers in stack
 move.b  d0,linkbuf				;moves value of d0 to linkbuf? or address?
 move.w  #1,-(a7)				;moves the value 1 into stack
 pea	 linkbuf(PC)				;help?  something about program counter
 jsr tios::transmit				;rom call to send data (what exactly are the 
								;parameters and what registers are destroyed?
								;i'm guessing that d0-d1/a0-a1 are affected)
 addq	 #6,a7					;moves the stack pointer back
 movem.l (a7)+,d0-d1/a0-a1		;restores register values.
 rts

ReceiveByte:
 movem.l d1/a0-a1,-(a7)			;saves register values
 clr.b	 linkbuf					;clears linkbuf
 move.w  #1,-(a7)				;moves the value 1 into stack
 pea	 linkbuf(PC)				;help again
 jsr tios::receive					;rom call (again, what parameters etc.)
 addq	 #6,a7					;moves stack pointer back
 clr.l	 d0						;clears d0
 move.b  linkbuf(PC),d0			;help here
 movem.l (a7)+,d1/a0-a1			;restores registers
 rts

somebody please help.  as you can see, i don't know very much on account of my
being an idiot.  i desperately await your wisdom.

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