MC68000 Instruction Execution Times
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MC68000 Instruction Execution Times
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These are the times for instructons, most of it is self
explanitory.
On the ST at 8 Mhz you need to round all times to multiples of
four. i.e 10 becomes 12. Please note that execution instruction
times are generally irrelevant when you have a instruction cache,
ie a greater than 68000 processor and i doubt that these numbers
will hold true for anything except a 68000 even if you turn the
cache off. Also note that it isn't usally worth spending ages trying
to optimize your code by using faster instructions. If you're code
is to slow, then you wil probably need to use a different method to
acheive your aims.
MOVE Instructions:
d(an
.b.w/.l dn an (an) (an)+ -(an) d(an) ,dn) abs.s abs.l
dn 4/4 4/4 8/12 8/12 8/14 12/16 14/18 12/16 16/20
an 4/4 4/4 8/12 8/12 8/14 12/16 14/18 12/16 16/20
(an) 8/12 8/12 12/20 12/20 12/20 16/24 18/26 16/24 20/28
(an)+ 8/12 8/12 12/20 12/20 12/20 16/24 18/26 16/24 20/28
-(an) 10/14 10/14 14/22 14/22 14/22 18/26 20/28 18/26 22/30
d(an) 12/16 12/16 16/24 16/24 16/24 20/28 22/30 20/28 24/32
d(an,dn) 14/18 14/18 18/26 18/26 18/26 22/30 24/32 22/30 26/34
abs.s 12/16 12/16 16/24 16/24 16/24 20/28 22/30 20/28 24/32
abs.l 16/20 16/20 20/28 20/28 20/28 24/32 26/34 24/32 28/36
d(pc) 12/16 12/16 16/24 16/24 16/24 20/28 22/30 20/28 24/32
d(pc,dn) 14/18 14/18 18/26 18/26 18/26 22/30 24/32 22/30 26/34
Immediate 8/12 8/12 12/20 12/20 12/20 16/24 18/26 16/24 20/28
----------------------------------------------------------------------
Time to calculate effective addresses.
d(an d(pc
(an) (an)+ -(an) d(an) ,dn) abs.s abs.l d(pc) ,dn) Imm
.b.w/.l 4/8 4/8 6/10 8/12 10/14 8/12 12/16 8/12 10/14 4/8
The time taken to calculate the effective address must be added to
instructions that affect a memory address.
----------------------------------------------------------------------
Standard Instructions:
.b.w/.l ea,an ea,dn dn,mem
add 8/6(8) 4/6(8) 8/12 (8) time if effective address
and - 4/6(8) 8/12 is direct
cmp 6/6 4/6 -
divs - 158max - Add effective address times
divu - 140max - from above for memory
eor - 4/8 8/12 addresses.
muls - 70max -
mulu - 70max -
or - 4/6(8) 8/12
sub 8/6(8) 4/6(8) 8/12
Immediate Instructions
.b.w/.l #,dn #,an #,mem
addi 8/16 - 12/20
addq 4/8 8/8 8/12 Moveq.l only
andi 8/16 - 12/20 nbcd+tas.b only
cmpi 8/14 8/14 8/12
eori 8/16 - 12/20 scc false/true
moveq 4 - -
ori 8/16 - 12/20 add effective address
subi 8/16 - 12/20 times from above
subq 4/8 8/8 8/12 for mem addresses
clr 4/6 4/6 8/12 single operand
nbcd 6 6 8 instructions
neg 4/6 4/6 8/12
negx 4/6 4/6 8/12
not 4/6 4/6 8/12
scc 4/6 4/6 8/8
tas 4 4 10
tst 4/4 4/4 4/4
Shift/rotate instructions.
.b.w/.l dn an mem
asr,asl 6/8 6/8 8 memory is byte only
lsr,lsl 6/8 6/8 8 register add 2x
ror,rol 6/8 6/8 8 shift count
roxr,roxl 6/8 6/8 8
d(an d(pc
(an) (an)+ -(an) d(an) ,dn) abs.s abs.l d(pc) ,dn)
jmp 8 - - 10 14 10 12 10 14
jsr 16 - - 18 22 18 20 18 22
lea 4 - - 8 12 8 12 8 12
pea 12 - - 16 20 16 20 16 20
movem t=4
m>r 12 12 - 16 18 16 20 16 18
movem t=5
r>m 8 - 8 12 14 12 16 - -
movem add t x number of registers for .w
movem add 2t x number of registers for .l
Bit Instructions
.b/.l register .l memory .b
only only
bchg 8/12 8/12
bclr 10/14 8/12
bset 8/12 8/12
btst 6/10 4/8
Exceptions Periods
Address Error 50
Bus Error 50
Interrupt 44
Illegal Instr. 34
Privilege Viol. 34
Trace 34
Other Instructions
add effective address times from above for memory addresses
.b.w/.l dn,dn m,m
addx 4/8 18/30
cmpm - 12/20
subx 4/8 18/30
abcd 6 18 .b only
sbcd 6 18 .b only
Bcc .b/.w 10/10 8/12
bra .b/.w 10/10 -
bsr .b/.w 18/18 -
DBcc t/f 10 12/14
chk - 40 max 8
trap - 34 -
trapv - 34 4
reg<>mem
movep .w/.l 16/24
Reg Mem Reg
andi to ccr 20 - move from usp 4
andi to sr 20 - nop 4
eori to ccr 20 - ori to ccr 20
eori to sr 20 - ori to sr 20
exg 6 - reset 132
ext 4 - rte 20
link 18 - rtr 20
move to ccr 12 12 rts 16
move to sr 12 12 stop 4
move from sr 6 8 swap 4
move to usp 4 - unlk 12
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