68k instructions timings
TODO: CSS template for cputiming is ugly and broken.
Mirroring information from http://oldwww.nvg.ntnu.no/amiga/MC680x0_Sections/mc68000timing.HTML
The number of bus read and write cycles is shown in parenthesis as (r/w).
In the following tables the headings have the following meanings:
- An : Address register operand
- Dn : Data register operand
- ea : Operand specified by an effective address
- M : Memory effective address operand
To get the execution time, multiply the cycles count by 83.33ns (1/12MHz).
A VBlank interrupt lasts exactly 40 lines * 384 pixels * 2 = 30720 cycles (2.56ms).
Effective address operand calculation
This table lists the number of clock periods required to compute an instruction's effective address. It includes fetching of any extension words, the address computation, and fetching of the memory operand.
Note: there are no write cycles involved in processing the effective address.
| Syntax | Adressing mode | B,W | L |
| Dn | Data register direct | 0(0/0) | 0(0/0) |
| An | Address register direct | 0(0/0) | 0(0/0) |
| (An) | Address register indirect | 4(1/0) | 8(2/0) |
| (An)+ | Address register indirect, post inc. | 4(1/0) | 8(2/0) |
| -(An) | Address register indirect, pre dec. | 6(1/0) | 10(2/0) |
| d(An) | Address register indirect, displacement | 8(2/0) | 12(3/0) |
| d(An,ix) | Address register indirect, index | 10(2/0) | 14(3/0) |
| xxx.w | Absolute short | 8(2/0) | 12(3/0) |
| xxx.l | Absolute long | 12(3/0) | 16(4/0) |
| d(PC) | PC with displacement | 8(2/0) | 12(3/0) |
| d(PC,ix) | PC with index | 10(2/0) | 14(3/0) |
| #xxx | Immediate | 4(1/0) | 8(2/0) |
The size of the index register (ix) does not affect execution time
Move instructions
These following two tables indicate the number of clock periods for the move instruction. This data includes instruction fetch, operand reads, and operand writes.
Byte and word
| Dn | An | (An) | (An)+ | -(An) | d(An) | d(An,ix) | xxx.W | xxx.L | |
|---|---|---|---|---|---|---|---|---|---|
| Dn | 4(1/0) | 4(1/0) | 8(1/1) | 8(1/1) | 8(1/1) | 12(2/1) | 14(2/1) | 12(2/1) | 16(3/1) |
| An | 4(1/0) | 4(1/0) | 8(1/1) | 8(1/1) | 8(1/1) | 12(2/1) | 14(2/1) | 12(2/1) | 16(3/1) |
| (An) | 8(2/0) | 8(2/0) | 12(2/1) | 12(2/1) | 12(2/1) | 16(3/1) | 18(3/1) | 16(3/1) | 20(4/1) |
| (An)+ | 8(2/0) | 8(2/0) | 12(2/1) | 12(2/1) | 12(2/1) | 16(3/1) | 18(3/1) | 16(3/1) | 20(4/1) |
| -(An) | 10(2/0) | 10(2/0) | 14(2/1) | 14(2/1) | 14(2/1) | 18(3/1) | 20(4/1) | 18(3/1) | 22(4/1) |
| d(An) | 12(3/0) | 12(3/0) | 16(3/1) | 16(3/1) | 16(3/1) | 20(4/1) | 22(4/1) | 20(4/1) | 24(5/1) |
| d(An,ix) | 14(3/0) | 14(3/0) | 18(3/1) | 18(3/1) | 18(3/1) | 22(4/1) | 24(4/1) | 22(4/1) | 26(5/1) |
| xxx.W | 12(3/0) | 12(3/0) | 16(3/1) | 16(3/1) | 16(3/1) | 20(4/1) | 22(4/1) | 20(4/1) | 24(5/1) |
| xxx.L | 16(4/0) | 16(4/0) | 20(4/1) | 20(4/1) | 20(4/1) | 24(5/1) | 26(5/1) | 24(5/1) | 28(6/1) |
| d(PC) | 12(3/0) | 12(3/0) | 16(3/1) | 16(3/1) | 16(3/1) | 20(4/1) | 22(4/1) | 20(4/1) | 24(5/1) |
| d(PC,ix) | 14(3/0) | 14(3/0) | 18(3/1) | 18(3/1) | 18(3/1) | 22(4/1) | 24(4/1) | 22(4/1) | 26(5/1) |
| #xxx | 8(2/0) | 8(2/0) | 12(2/1) | 12(2/1) | 12(2/1) | 16(3/1) | 18(3/1) | 16(3/1) | 20(4/1) |
The size of the index register (ix) does not affect execution time.
Long
| Dn | An | (An) | (An)+ | -(An) | d(An) | d(An,ix) | xxx.W | xxx.L | |
|---|---|---|---|---|---|---|---|---|---|
| Dn | 4(1/0) | 4(1/0) | 12(1/2) | 12(1/2) | 12(1/2) | 16(2/2) | 18(2/2) | 16(2/2) | 20(3/2) |
| An | 4(1/0) | 4(1/0) | 12(1/2) | 12(1/2) | 12(1/2) | 16(2/2) | 18(2/2) | 16(2/2) | 20(3/2) |
| (An) | 12(3/0) | 12(3/0) | 20(3/2) | 20(3/2) | 20(3/2) | 24(4/2) | 26(4/2) | 24(4/2) | 28(5/2) |
| (An)+ | 12(3/0) | 12(3/0) | 20(3/2) | 20(3/2) | 20(3/2) | 24(4/2) | 26(4/2) | 24(4/2) | 28(5/2) |
| -(An) | 14(3/0) | 14(3/0) | 22(3/2) | 22(3/2) | 22(3/2) | 26(4/2) | 28(4/2) | 26(4/2) | 30(5/2) |
| d(An) | 16(4/0) | 16(4/0) | 24(4/2) | 24(4/2) | 24(4/2) | 28(5/2) | 30(5/2) | 28(5/2) | 32(6/2) |
| d(An,ix) | 18(4/0) | 18(4/0) | 26(4/2) | 26(4/2) | 26(4/2) | 30(5/2) | 32(5/2) | 30(5/2) | 34(6/2) |
| xxx.W | 16(4/0) | 16(4/0) | 24(4/2) | 24(4/2) | 24(4/2) | 28(5/2) | 30(5/2) | 28(5/2) | 32(6/2) |
| xxx.L | 20(5/0) | 20(5/0) | 28(5/2) | 28(5/2) | 28(5/2) | 32(6/2) | 34(6/2) | 32(6/2) | 36(7/2) |
| d(PC) | 16(4/0) | 16(4/0) | 24(4/2) | 24(4/2) | 24(4/2) | 28(5/2) | 30(5/2) | 28(5/2) | 32(5/2) |
| d(PC,ix) | 18(4/0) | 18(4/0) | 26(4/2) | 26(4/2) | 26(4/2) | 30(5/2) | 32(5/2) | 30(5/2) | 34(6/2) |
| #xxx | 12(3/0) | 12(3/0) | 20(3/2) | 20(3/2) | 20(3/2) | 24(4/2) | 26(4/2) | 24(4/2) | 28(5/2) |
The size of the index register (ix) does not affect execution time.
Standard instructions
The number of clock periods shown in this table indicates the time required
to perform the operations, store the results and read the next instruction.
The number of clock periods and the number of read and write cycles must be
added respectively to those of the effective address calculation where
indicated.
instruction Size op<ea>,An ^ op<ea>,Dn op Dn,<M>
ADD byte,word 8(1/0) + 4(1/0) + 8(1/1) +
long 6(1/0) +** 6(1/0) +** 12(1/2) +
AND byte,word - 4(1/0) + 8(1/1) +
long - 6(1/0) +** 12(1/2) +
CMP byte,word 6(1/0) + 4(1/0) + -
long 6(1/0) + 6(1/0) + -
DIVS - - 158(1/0) +* -
DIVU - - 140(1/0) +* -
EOR byte,word - 4(1/0) *** 8(1/1) +
long - 8(1/0) *** 12(1/2) +
MULS - - 70(1/0) +* -
MULU - - 70(1/0) +* -
OR byte,word - 4(1/0) +** 8(1/1) +
long - 6(1/0) +** 12(1/2) +
SUB byte,word 8(1/0) + 4(1/0) + 8(1/1) +
long 6(1/0) +** 6(1/0) +** 12(1/2) +
notes: + Add effective address calculation time
^ Word or long only
* Indicates maximum value
** The base time of six clock periods is increased to eight
if the effective address mode is register direct or
immediate (effective address time should also be added)
*** Only available effective address mode is data register direct
DIVS,DIVU - The divide algorithm used by the MC68000 provides less
than 10% difference between the best and the worst case
timings.
MULS,MULU - The multiply algorithm requires 38+2n clocks where
n is defined as:
MULU: n = the number of ones in the <ea>
MULS: n = concatanate the <ea> with a zero as the LSB;
n is the resultant number of 10 or 01 patterns
in the 17-bit source; i.e., worst case happens
when the source is $5555
Immediate instructions
The number of clock periods periods shown in this table includes the time to
fetch immediate operands, perform the operations, store the results and read
the next operation. The number of clock periods and the number of read and
write cycles must be added respectively to those of the effective address
calculation where indicated.
instruction size op #,Dn op #,An op #,M
ADDI byte,word 8(2/0) - 12(2/1) +
long 16(3/0) - 20(3/2) +
ADDQ byte,word 4(1/0) 8(1/0) * 8(1/1) +
long 8(1/0) 8(1/0) 12(1/2) +
ANDI byte,word 8(2/0) - 12(2/1) +
long 16(3/0) - 20(3/1) +
CMPI byte,word 8(2/0) - 8(2/0) +
long 14(3/0) - 12(3/0) +
EORI byte,word 8(2/0) - 12(2/1) +
long 16(3/0) - 20(3/2) +
MOVEQ long 4(1/0) - -
ORI byte,word 8(2/0) - 12(2/1) +
long 16(3/0) - 20(3/2) +
SUBI byte,word 8(2/0) - 12(2/1) +
long 16(3/0) - 20(3/2) +
SUBQ byte,word 4(1/0) 8(1/0) * 8(1/1) +
long 8(1/0) 8(1/0) 12(1/2) +
+ Add effective address calculation time
* word only
Single operand instructions
This table indicates the number of clock periods for the single operand
instructions. The number of clock periods and the number of read and write cycles
must be added respectively to those of the effective address calculation
where indicated.
instruction size register memory
CLR byte,word 4(1/0) 8(1/1) +
long 6(1/0) 12(1/2) +
NBCD byte 6(1/0) 8(1/1) +
NEG byte,word 4(1/0) 8(1/1) +
long 6(1/0) 12(1/2) +
NEGX byte,word 4(1/0) 8(1/1) +
long 6(1/0) 12(1/2) +
NOT byte,word 4(1/0) 8(1/1) +
long 6(1/0) 12(1/2) +
Scc byte,false 4(1/0) 8(1/1) +
byte,true 6(1/0) 8(1/1) +
TAS # byte 4(1/0) 10(1/1) +
TST byte,word 4(1/0) 4(1/0) +
long 4(1/0) 4(1/0) +
+ add effective address calculation time
# This instruction should never be used on the Amiga as its invisiable
read/write cycle can disrupt system DMA.
Shift and rotate instructions
This table indicates the number of clock periods for the shift and rotate
instructions. The number of clock periods and the number of read and write
cycles must be added respectively to those of the effective address
calculation where indicated.
instruction size register memory
ASR,ASL byte,word 6+2n(1/0) 8(1/1) +
long 8+2n(1/0) -
LSR,LSL byte,word 6+2n(1/0) 8(1/1) +
long 8+2n(1/0) -
ROR,ROL byte,word 6+2n(1/0) 8(1/1) +
long 8+2n(1/0) -
ROXR,ROXL byte,word 6+2n(1/0) 8(1/1) +
long 8+2n(1/0) -
+ add effective address calculation time
n is the shift or rotate count
Bit manipulation instructions
This table indicates the number of clock periods required for the bit
manipulation instructions. The number of clock periods and the number of read and
write cycles must be added respectively to those of the effective address
calculation where indicated. Dynamic: register, static: immediate.
instruction size dynamic static
register memory register memory
BCHG byte - 8(1/1) + - 12(2/1) +
long 8(1/0) * - 12(2/0) * -
BCLR byte - 8(1/1) + - 12(2/1) +
long 10(1/0) * - 14(2/0) * -
BSET byte - 8(1/1) + - 12(2/1) +
long 8(1/0) * - 12(2/0) * -
BTST byte - 4(1/0) + - 8(2/0) +
long 6(1/0) - 10(2/0) -
+ add effective address calculation time
* indicates maximum value
Conditional instructions
| Syntax | Displacement | Branch taken | Not taken |
| Bcc | byte | 10(2/0) | 8(1/0) |
| word | 10(2/0) | 12(1/0) | |
| BRA | byte | 10(2/0) | |
| word | 10(2/0) | ||
| BSR | byte | 18(2/2) | |
| word | 18(2/2) | ||
| DBcc | cc true | 12(2/0) | |
| cc false | 10(2/0) | 14(3/0) |
JMP, JSR, LEA, PEA and MOVEM instructions
This Table indicates the number of clock periods required for the jump,
jump-to-subroutine, load effective address, push effective address and
move multiple registers instructions.
instr size (An) (An)+ -(An) d(An)
JMP - 8(2/0) - - 10(2/0)
JSR - 16(2/2) - - 18(2/2)
LEA - 4(1/0) - - 8(2/0)
PEA - 12(1/2) - - 16(2/2)
MOVEM word 12+4n 12+4n - 16+4n
M->R (3+n/0) (3+n/0) - (4+n/0)
long 12+8n 12+8n - 16+8n
(3+2n/0) (3+2n/0) - (4+2n/0)
MOVEM word 8+4n - 8+4n 12+4n
R->M (2/n) - (2/n) (3/n)
long 8+8n - 8+8n 12+8n
(2/2n) - (2/2n) (3/2n)
instr size d(An,ix)+ xxx.W xxx.L d(PC) d(PC,ix)*
JMP - 14(3/0) 10(2/0) 12(3/0) 10(2/0) 14(3/0)
JSR - 22(2/2) 18(2/2) 20(3/2) 18(2/2) 22(2/2)
LEA - 12(2/0) 8(2/0) 12(3/0) 8(2/0) 12(2/0)
PEA - 20(2/2) 16(2/2) 20(3/2) 16(2/2) 20(2/2)
MOVEM word 18+4n 16+4n 20+4n 16+4n 18+4n
M->R (4+n/0) (4+n/0) (5+n/0) (4+n/0) (4+n/0)
long 18+8n 16+8n 20+8n 16+8n 18+8n
(4+2n/0) (4+2n/0) (5+2n/0) (4+2n/0) (4+2n/0)
MOVEM word 14+4n 12+4n 16+4n - -
R->M (3/n) (3/n) (4/n) - -
long 14+8n 12+8n 16+8n - -
(3/2n) (3/2n) (4/2n) - -
n is the number of registers to move
* is the size of the index register (ix) does not affect the instruction's
execution time
Multi-precision instructions
This table indicates the number of clock periods for the multi-precision
instructions. The number of clock periods includes the time to fetch both
operands, perform the operations, store the results and read the next
instructions.
instruction size op Dn,Dn op M,M
ADDX byte,word 4(1/0) 18(3/1)
long 8(1/0) 30(5/2)
CMPM byte,word - 12(3/0)
long - 20(5/0)
SUBX byte,word 4(1/0) 18(3/1)
long 8(1/0) 30(5/2)
ABCD byte 6(1/0) 18(3/1)
SBCD byte 6(1/0) 18(3/1)
Miscellaneous instructions
This table indicates the number of clock periods for the following
miscellaneous instructions. The number of clock periods and plus the number
of read and write cycles must be added to those of the effective address
calculation where indicated.
instruction size register memory
ANDI to CCR byte 20(3/0) -
ANDI to SR word 20(3/0) -
CHK - 10(1/0) + -
EORI to CCR byte 20(3/0) -
EORI to SR word 20(3/0) -
ORI to CCR byte 20(3/0) -
ORI to SR word 20(3/0) -
MOVE from SR - 6(1/0) 8(1/1)+
MOVE to CCR - 12(1/0) 12(1/0)+
MOVE to SR - 12(1/0) 12(1/0)+
EXG - 6(1/0) -
EXT word 4(1/0) -
long 4(1/0) -
LINK - 16(2/2) -
MOVE from USP - 4(1/0) -
MOVE to USP - 4(1/0) -
NOP - 4(1/0) -
RESET - 132(1/0) -
RTE - 20(5/0) -
RTR - 20(5/0) -
RTS - 16(4/0) -
STOP - 4(0/0) -
SWAP - 4(1/0) -
TRAPV (No Trap) - 4(1/0) -
UNLK - 12(3/0) -
+ add effective address calculation time
Move Peripheral instructions
instruction size register->memory memory->register
MOVEP word 16(2/2) 16(4/0)
long 24(2/4) 24(6/0)
Exception processing
This table indicates the number of clock periods for exception processing.
The number of clock periods includes the time for all stacking, the vector
fetch and the fetch of the first two instruction words of the handler routine.
exception periods
address error 50(4/7)
bus error 50(4/7)
CHK instruction (trap taken) 44(5/3)+
Divide by Zero 42(5/3)
illegal instruction 34(4/3)
interrupt 44(5/3)*
privilege violation 34(4/3)
_____
RESET ** 40(6/0)
trace 34(4/3)
TRAP instruction 38(4/3)
TRAPV instruction (trap taken) 34(4/3)
+ add effective address calculation time
* the interrupt acknowledge cycle is assumed to take four
clock periods
_____ ____
** indicates the time from when RESET and HALT are first
sampled as negated to when instruction execution starts