Okay, here's my first question. It's a pretty tough one, but here goes:
I downloaded this linking code for 2-player matches in the game. Originally, these 2 routines set/cleared the zero flags to indicated failed/good links. But I had to change it set/clear the carry flags instead, in order to send zeros too. Here's the problem: The prog works fine if a link is present, but the linksend code will always returns a success value after it tries to send; even if there's no link present! I can't seem to find out what's going wrong. The linkget routine works as planned...
Code:
;;################################################
;; #
;; linkget #
;; #
;; Receive 1 byte through link port. #
;; (includes timeout) #
;; #
;; IN: -nothing- #
;; OUT: Carry Set. Link failed #
;; NoCarry Link successful #
;; C=byte received #
;; #
;;------------------------------------------------
;; linksend #
;; #
;; Send byte in A register through link port #
;; (Use ALPHA to cancel transmission #
;; #
;; IN: A = byte to send #
;; OUT: NoCarry Byte sent! #
;; Carry Set Transfer canceled #
;; #
;;------------------------------------------------
linkget:;RECIEVES A BYTE
push hl;save hl
ld hl,16383;timeout value you may change this if you want (you could also
;use the d register here for a smaller timeout)
ld e,1;e is for the or'ing below
ld c,0; byte that will be received
ld b,8; 8 bits = 1 byte counter
ld a,$C0;both wires active
out (0),a;send to port
checkresponse:
call checktimeoutget ;check timeout
in a,(0);read from port
and 3 ;mask off the rest of a reg
cp 3 ;if its 3 then both wires are still active
;(meaning no response from other calc yet)
jr z,checkresponse;if not 3 then other calc says 'ready'
othercalcready:
cp 2 ;if the send routine on other calc says bit 1 of a (a=2 now)
;is sent then it is a zero that will be sent
;(white is active, red is not, so go turn red wire on)
jr z,getlinkzero;if so go get the zero
ld a,c
or e ;this makes the bit of the current bit ((8-bitcounter)+1)
;and turns on that bit and
ld c,a;stores it back to a
ld a,$D4;turn on white wire
out (0),a;send to linkport
jr sendgotbit
getlinkzero:
ld a,$E8;red wire on (red = 0, white = 1)
out (0),a;send to port
sendgotbit:
call checktimeoutget
in a,(0);check to see if both wires not active
;(sending calc said i got your response that you got that bit)
and 3
jr z,sendgotbit
ld a,$C0;both wires on
out (0),a
rl e;next bit to do
djnz checkresponse
ld a,c;byte recived.
or a ;do the comparision
pop hl;get saved hl
scf ;; Indicate successful transfer
ccf ;;
ret ;return back with recieved byte
checktimeoutget:
dec hl;hl-1 ->hl
ld a,l;if hl=0
or h ;
ret nz;return if hl!=0 (it starts at 16383)
pop hl;get saved hl
pop de;trash last stack address so youll
;return to the lable that called linkget
;; xor a;say no byte reciecved
scf ;; Indicate link error
ret ;return back (timeout occured)
;------------------------------------------------------------------------------------
linksend:;SENDS A BYTE
ld b,8;bit counter
ld c,a;byte to send
ld a,$C0;both wires active
out (0),a;send to port
checkreceivecalc:
call checksendcanceled
in a,(0);read from port
and 3 ;mask off all but the first two (bit 0,and 1) of a
cp 3 ;if 3 then other calc has both wires active
;(other calc is ready)
jr nz,checkreceivecalc;other calc is ready if both wires active
;reloop untill other calc is ready or you press exit
othercalcready2:
ld a,c;byte to send into a
and 1;only the first bit of it counts (its checked like this):
;a reg = % 0 0 0 0 0 0 0 0
;bit number 7 6 5 4 3 2 1 0
;and'ing by 1 gets rid of all but --------^----- that bit there
jr z,linksendone;if so send bit == 1
linksendzero:
ld a,$E8;red wire on
out (0),A;send to port
jr checkifbitgot
linksendone:
ld a,$D4;white wire on (on and active are same thing)
out (0),A;send it to linkport
checkifbitgot:
call checksendcanceled
in a,(0);read from port
and 3; if its anything other than 3 that means
;other calc (recieveing end) got the bit
jr nz,checkifbitgot;reloop until bit got
ld a,$C0 ;both wires active
out (0),A;send to port
srl c ;next bit of c to be checked (shifts it all one to right)
djnz checkreceivecalc
;; xor a;a=0 byte=sent
scf ;; Indicate successful transfer
ccf ;;
ret ;go back to where linksend was called
checksendcanceled:
; ld a,%00111111;checks keyport if exit is pressed
; out (1),a
; in a,(1)
; bit 6,a
push hl
call GET_KEY
pop hl
cp G_ALPHA
ret nz
pop de;trash checksendcanceled call
pop de;trash linksend call
scf ;; Indicate link error
ret ;; Return with the bad news. A = G_ALPHA
This code is basically the centerpeice of the game, so it's vital I find the bug before I can move on... 
Last edited by Guest on 12 Feb 2004 11:51:45 pm; edited 1 time in total |
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