| [hatari-devel] EXA demo Entracte : Improvement in search |
[ Thread Index |
Date Index
| More lists.tuxfamily.org/hatari-devel Archives
]
Hi,
I've managed to see EXA Entracte demo under current hatari (that's a
nice demo).
In general, it returns immediatly to the desktop.
I write this mail to keep a trace of my recent search with this demo and
share it with you.
I explain how to see it and I give you the info where it goes wrong (I
don't understand it completly but maybe it'll ring a bell for you).
So, I've done the following to see it :
> b pc=text
> c
Run "entracte.prg"
You put a breakpoint at the beginning of the demo, then disasm the first
instructions.
>d
$0004e7a8 : 4879 0020 0000 pea $200000
$0004e7ae : 4e41 trap #1
$0004e7b0 : 41fa 021a lea $4e9cc(pc),a0
$0004e7b4 : 4dfa 0014 lea $4e7ca(pc),a6
$0004e7b8 : 4bfa 01d6 lea $4e990(pc),a5
$0004e7bc : 21ce 030c move.l a6,$030c.w
$0004e7c0 : 21cd 0310 move.l a5,$0310.w
$0004e7c4 : 4e96 jsr (a6)
$0004e7c6 : 4e95 jsr (a5)
$0004e7c8 : 4ed0 jmp (a0) ;
<------ Breakpoint here
Then, you put a breakpoint at the jump instruction
> b pc=$4e7c8
> c
When you reach the breakpoint, you execute it, then, disasm the code again.
> c 1
> d
$0004e9e8 : 4ff9 0008 ce48 lea $8ce48,sp
$0004e9ee : 203c 0040 0000 move.l #$400000,d0
$0004e9f4 : 0480 0008 d24a subi.l #$8d24a,d0
$0004e9fa : 0480 0000 3000 subi.l #$3000,d0
$0004ea00 : 6b00 0130 bmi $4eb32
$0004ea04 : 4879 0058 ffff pea $58ffff
$0004ea0a : 4e4e trap #$e
$0004ea0c : 33c0 0008 ce48 move.w d0,$8ce48
>
$0004ea12 : 6100 018c bsr $4eba0
$0004ea16 : 4e7a 0002 movec cacr,d0
$0004ea1a : 23c0 0004 fdca move.l d0,$4fdca
$0004ea20 : 203c 0000 3111 move.l #$3111,d0
$0004ea26 : 4e7b 0002 movec d0,cacr
$0004ea2a : 6100 0128 bsr $4eb54
<----- call subroutine to compute D0
$0004ea2e : b07c 4100 cmp.w #$4100,d0
$0004ea32 : 6f00 00e8 ble $4eb1c
<----- quit the demo
$0004ea36 : b07c 4200 cmp.w #$4200,d0
$0004ea3a : 6e00 00e0 bgt $4eb1c
<----- quit the demo
The problem is in the 5 last lines : the code test for a min and max
value for register DO.
if D0 is not between $4100 and $4200, the code goes to $4eb1c and this
quit the demo immediatly.
So, I've added a breakpoint at the beginning of the first test and I
change the value of D0 to $4150.
b pc=$4ea2e
r d0=$4150
c
And the demo runs well to the end.
; ------ Now, let's see what happens here ;)
The problem is in the 5 last instructions test:
- it computes a value into D0 (bsr $4eb54)
- then, it tests if this value is between $4100 and $4200
- if not, it quits the demo immediatly
The subroutine codeis given just below.
From what I understand, they wait 1 VBL, then use d0 as a counter
during 1 VBL, then test the value of D0.
Does this code (the bsr subroutine part) tells something to you ?
; These lines seems to wait a VBL
$0004eb72 : 4278 0468 clr.w $0468.w
$0004eb76 : 4a78 0468 tst.w $0468.w
$0004eb7a : 67fa beq.s $4eb76
; The next ones seem to wait another VBL and increase D0 during this time.
; Here is the code of the compute D0 subroutine
$0004eb54 : 2f38 fa06 move.l $fffffa06.w,-(sp)
$0004eb58 : 41f8 fa07 lea $fffffa07.w,a0
$0004eb5c : 7000 moveq #0,d0
$0004eb5e : 0188 0000 movep.w d0,0(a0)
$0004eb62 : 41f8 0080 lea $0080.w,a0
$0004eb66 : f010 DC.W $f010
$0004eb68 : 4200 clr.b d0
$0004eb6a : 0210 007f andi.b #$7f,(a0)
>
$0004eb6e : f010 4000 pmove (a0),tc
$0004eb72 : 4278 0468 clr.w $0468.w
$0004eb76 : 4a78 0468 tst.w $0468.w
$0004eb7a : 67fa beq.s $4eb76
$0004eb7c : 4278 0468 clr.w $0468.w
$0004eb80 : 7000 moveq #0,d0
$0004eb82 : 4a78 0468 tst.w $0468.w
$0004eb86 : 6600 0006 bne $4eb8e
>
$0004eb8a : 5240 addq.w #1,d0
$0004eb8c : 60f4 bra.s $4eb82
$0004eb8e : 41f8 0080 lea $0080.w,a0
$0004eb92 : 0010 0080 ori.b #$80,(a0)
$0004eb96 : f010 4000 pmove (a0),tc
$0004eb9a : 21df fa06 move.l (sp)+,$fffffa06.w
$0004eb9e : 4e75 rts
Regards
Laurent