When used with full 32-bit addresses (that is, non-zero data in the highest 8 bits), the bset and bclr instructions will frequently either corrupt data at the specified address or generate a runtime exception.
Attached is sample code that demonstrates this behavior as well as a runtime log. Note that, at the end of execution, the value of the byte at $FF2000 is $79. If the simulator were operating correctly, the expected value would be $0C.
I suspect that the simulator is not correctly dropping the high byte of the address, and that this issue also affect the bchg instruction. However, I have not personally tested anything other than bset and bclr.
(Apologies for the large copy/paste. The forum's attachment system will not allow me to upload .X68 or .txt files.)
Sample code:
Code:
ORG $1000
TestVar equ $FFFF2000
START:
lea TestVar, a0
move.b #0, (a0)
bclr #0, (a0)
bset #2, (a0)
bset #3, (a0)
SIMHALT
END START
*~Font name~Courier New~
*~Font size~10~
*~Tab type~1~
*~Tab size~4~
Runtime log:
Code:
EASy68K execution log file: 8/5/2015 3:51:14 PM
00FF2000: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF ----------------
D0=00000000 D4=00000000 A0=00000000 A4=00000000 T_S__INT___XNZVC
D1=00000000 D5=00000000 A1=00000000 A5=00000000 SR=0010000000000000
D2=00000000 D6=00000000 A2=00000000 A6=00000000 US=00FF0000
D3=00000000 D7=00000000 A3=00000000 A7=01000000 SS=01000000
PC=00001000 Code=41F9 FFFF2000 Line= 6 lea TestVar, a0
00FF2000: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF ----------------
D0=00000000 D4=00000000 A0=FFFF2000 A4=00000000 T_S__INT___XNZVC
D1=00000000 D5=00000000 A1=00000000 A5=00000000 SR=0010000000000000
D2=00000000 D6=00000000 A2=00000000 A6=00000000 US=00FF0000
D3=00000000 D7=00000000 A3=00000000 A7=01000000 SS=01000000
PC=00001006 Code=10BC 0000 Line= 7 move.b #0, (a0)
00FF2000: 00 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF ----------------
D0=00000000 D4=00000000 A0=FFFF2000 A4=00000000 T_S__INT___XNZVC
D1=00000000 D5=00000000 A1=00000000 A5=00000000 SR=0010000000000100
D2=00000000 D6=00000000 A2=00000000 A6=00000000 US=00FF0000
D3=00000000 D7=00000000 A3=00000000 A7=01000000 SS=01000000
PC=0000100A Code=0890 0000 Line= 9 bclr #0, (a0)
00FF2000: 70 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF p---------------
D0=00000000 D4=00000000 A0=FFFF2000 A4=00000000 T_S__INT___XNZVC
D1=00000000 D5=00000000 A1=00000000 A5=00000000 SR=0010000000000100
D2=00000000 D6=00000000 A2=00000000 A6=00000000 US=00FF0000
D3=00000000 D7=00000000 A3=00000000 A7=01000000 SS=01000000
PC=0000100E Code=08D0 0002 Line= 11 bset #2, (a0)
00FF2000: 75 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF u---------------
D0=00000000 D4=00000000 A0=FFFF2000 A4=00000000 T_S__INT___XNZVC
D1=00000000 D5=00000000 A1=00000000 A5=00000000 SR=0010000000000100
D2=00000000 D6=00000000 A2=00000000 A6=00000000 US=00FF0000
D3=00000000 D7=00000000 A3=00000000 A7=01000000 SS=01000000
PC=00001012 Code=08D0 0003 Line= 12 bset #3, (a0)
00FF2000: 79 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF y---------------
D0=00000000 D4=00000000 A0=FFFF2000 A4=00000000 T_S__INT___XNZVC
D1=00000000 D5=00000000 A1=00000000 A5=00000000 SR=0010000000000100
D2=00000000 D6=00000000 A2=00000000 A6=00000000 US=00FF0000
D3=00000000 D7=00000000 A3=00000000 A7=01000000 SS=01000000
PC=00001016 Code=FFFF FFFF Line= 14 SIMHALT
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