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Hi everybody,
I encounter a situation I can't explain for now with ROL.B and the Carry
flag in the 68030 state register.
My example program :
Clear d7
Set d0 to 9
rol.b d0 2 times with values $10 and $40 and check the C flag of the
state register after each rol.
rol.b d0 by $10 (if carry bit is set, add 1 to d7)
rol.b d0 by $40 (if carry bit is set, add 2 to d7)
Then I display the value of d7 on screen (0, 1, 2 or 3) depending of the
state of the Carry bit.
When I run the program, I can read on screen "3"; which means that the
carry bit was "1" for the 2 rol instructions.
When I trace the program under hatari debugger (which is supposed to be
non intrusive for the CPU), I can see that the second rol set the carry
bit to 0.
The result of D7 is 1 instead of 3.
When I run my "current project ;)", I have the feeling that sometimes
the carry bit is 0 and sometimes 1 but I can't find a general rule for this.
Any idea ?
Regards
Laurent
The example program :
clr.l d7
moveq #9,d0
moveq #$10,d1
moveq #$40,d2
rol.b d1,d0
bcc.s .test2
addq.w #1,d7
..test2: rol.b d2,d0
bcc.s .display_result
addq.w #2,d7
..display_result:
add.w #$32,d7
; Display the value of D7
move.w d7,-(sp) ; Offset 2
move.w #2,-(sp) ; Offset 0
trap #1 ; GEMDOS
addq.l #4,sp ; Correct stack
toto: bra.s toto
When I run it under hatari, I can read "3"
When I trace it (in another run), I can see :
Before the first rol.b by #$10
CPU=$2e1dc, VBL=1082, FrameCycles=198808, HBL=194, LineCycles=152, DSP=$51
$0002e1dc : e338 rol.b d1,d0
> r
D0 00000009 D1 00000010 D2 00000040 D3 00000000
D4 00000000 D5 00000000 D6 00000000 D7 00000000
A0 00000000 A1 00000000 A2 00000000 A3 00000000
A4 0002E290 A5 0002E27E A6 00DE0AC6 A7 00DE0AF8
USP 00DE0AF8 ISP 00008870 SFC 00000000 DFC 00000000
CACR 00003111 VBR 00000000 CAAR 00000000 MSP 00000000
T=00 S=0 M=0 X=0 N=0 Z=0 V=0 C=0 IMASK=3 STP=0
0: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
2: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
4: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
6: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
FPSR: 00000000 FPCR: 00000000 FPIAR: 00000000 N=0 Z=0 I=0 NAN=0
Prefetch 0002e1e0 5247e538 (1) 6402 (1) 5247 (1) e538 (1)
0002E1DC e338 ROL.B D1,D0
Next PC: 0002e1de
> c 1
Returning to emulation for 1 CPU instructions...
Just after the first rol.b , carry = 1
CPU=$2e1de, VBL=1082, FrameCycles=198808, HBL=194, LineCycles=152, DSP=$51
$0002e1de : 6402 bcc.s $2e1e2
> r
D0 00000009 D1 00000010 D2 00000040 D3 00000000
D4 00000000 D5 00000000 D6 00000000 D7 00000000
A0 00000000 A1 00000000 A2 00000000 A3 00000000
A4 0002E290 A5 0002E27E A6 00DE0AC6 A7 00DE0AF8
USP 00DE0AF8 ISP 00008870 SFC 00000000 DFC 00000000
CACR 00003111 VBR 00000000 CAAR 00000000 MSP 00000000
T=00 S=0 M=0 X=0 N=0 Z=0 V=0 C=1 IMASK=3 STP=0
0: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
2: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
4: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
6: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
FPSR: 00000000 FPCR: 00000000 FPIAR: 00000000 N=0 Z=0 I=0 NAN=0
Prefetch 0002e1e0 5247e538 (2) 5247 (1) e538 (1) 5247 (1)
0002E1DE 6402 BCC.B #$02 == $00000000 (F)
Next PC: 0002e1e0
> c 1
Returning to emulation for 1 CPU instructions...
CPU=$2e1e0, VBL=1082, FrameCycles=198816, HBL=194, LineCycles=160, DSP=$51
$0002e1e0 : 5247 addq.w #1,d7
> r
D0 00000009 D1 00000010 D2 00000040 D3 00000000
D4 00000000 D5 00000000 D6 00000000 D7 00000000
A0 00000000 A1 00000000 A2 00000000 A3 00000000
A4 0002E290 A5 0002E27E A6 00DE0AC6 A7 00DE0AF8
USP 00DE0AF8 ISP 00008870 SFC 00000000 DFC 00000000
CACR 00003111 VBR 00000000 CAAR 00000000 MSP 00000000
T=00 S=0 M=0 X=0 N=0 Z=0 V=0 C=1 IMASK=3 STP=0
0: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
2: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
4: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
6: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
FPSR: 00000000 FPCR: 00000000 FPIAR: 00000000 N=0 Z=0 I=0 NAN=0
Prefetch 0002e1e4 64025447 (1) e538 (1) 6402 (1) 5447 (1)
0002E1E0 5247 ADDQ.W #$01,D7
Next PC: 0002e1e2
> c 1
Returning to emulation for 1 CPU instructions...
Just before the second rol.b by #$40
CPU=$2e1e2, VBL=1082, FrameCycles=198816, HBL=194, LineCycles=160, DSP=$51
$0002e1e2 : e538 rol.b d2,d0
> r
D0 00000009 D1 00000010 D2 00000040 D3 00000000
D4 00000000 D5 00000000 D6 00000000 D7 00000001
A0 00000000 A1 00000000 A2 00000000 A3 00000000
A4 0002E290 A5 0002E27E A6 00DE0AC6 A7 00DE0AF8
USP 00DE0AF8 ISP 00008870 SFC 00000000 DFC 00000000
CACR 00003111 VBR 00000000 CAAR 00000000 MSP 00000000
T=00 S=0 M=0 X=0 N=0 Z=0 V=0 C=0 IMASK=3 STP=0
0: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
2: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
4: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
6: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
FPSR: 00000000 FPCR: 00000000 FPIAR: 00000000 N=0 Z=0 I=0 NAN=0
Prefetch 0002e1e4 64025447 (2) 6402 (1) 5447 (1) 6402 (1)
0002E1E2 e538 ROL.B D2,D0
Next PC: 0002e1e4
> c 1
Returning to emulation for 1 CPU instructions...
Just after the second rol, Carry bit is still 0
CPU=$2e1e4, VBL=1082, FrameCycles=198816, HBL=194, LineCycles=160, DSP=$51
$0002e1e4 : 6402 bcc.s $2e1e8
> r
D0 00000009 D1 00000010 D2 00000040 D3 00000000
D4 00000000 D5 00000000 D6 00000000 D7 00000001
A0 00000000 A1 00000000 A2 00000000 A3 00000000
A4 0002E290 A5 0002E27E A6 00DE0AC6 A7 00DE0AF8
USP 00DE0AF8 ISP 00008870 SFC 00000000 DFC 00000000
CACR 00003111 VBR 00000000 CAAR 00000000 MSP 00000000
T=00 S=0 M=0 X=0 N=0 Z=0 V=0 C=0 IMASK=3 STP=0
0: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
2: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
4: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
6: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
FPSR: 00000000 FPCR: 00000000 FPIAR: 00000000 N=0 Z=0 I=0 NAN=0
Prefetch 0002e1e4 64025447 (2) 5447 (1) 6402 (1) 5447 (1)
0002E1E4 6402 BCC.B #$02 == $00000000 (T)
Next PC: 0002e1e6
> c 1
Returning to emulation for 1 CPU instructions...
D7 = 1 instead of the awaited 3
CPU=$2e1e8, VBL=1082, FrameCycles=198832, HBL=194, LineCycles=176, DSP=$51
$0002e1e8 : de7c 0032 add.w #$32,d7
> r
D0 00000009 D1 00000010 D2 00000040 D3 00000000
D4 00000000 D5 00000000 D6 00000000 D7 00000001
A0 00000000 A1 00000000 A2 00000000 A3 00000000
A4 0002E290 A5 0002E27E A6 00DE0AC6 A7 00DE0AF8
USP 00DE0AF8 ISP 00008870 SFC 00000000 DFC 00000000
CACR 00003111 VBR 00000000 CAAR 00000000 MSP 00000000
T=00 S=0 M=0 X=0 N=0 Z=0 V=0 C=0 IMASK=3 STP=0
0: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
2: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
4: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
6: 7FFF-FFFFFFFF-FFFFFFFF +nan 7FFF-FFFFFFFF-FFFFFFFF +nan
FPSR: 00000000 FPCR: 00000000 FPIAR: 00000000 N=0 Z=0 I=0 NAN=0
Prefetch 0002e1ec 3f073f3c (1) 0032 (1) 3f07 (1) 3f3c (1)
0002E1E8 de7c 0032 ADD.W #$0032,D7
Next PC: 0002e1ec