Fixed cycle delay

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Shortest possible CPU code that creates N cycles of delay, depending on constraints.

Code

All code samples are written for CA65.

Assumptions:

  • No page wrap occurs during any branch instruction. If a page wrap occurs, it adds +1 cycle for each loop, completely thwarting the accurate delay.
  • No interrupt / NMI occurs during the delay code.

It is permissible for DMA to steal cycles during the loops. If you are expecting that to happen, you have to manually adjust the delay cycle count (and it is in fact possible to do so) in order to get the correct delay.

Explanations on the requirements

  • @rts12 means you know a memory address that contains byte $60 (RTS).

cycle instruction that fits your constraints (such as LDA $00), followed by RTS.

Instructions, addressing modes, byte counts, cycle counts and notes

Addressing mode Instruction type Bytes Cycle count Example instruction Notes
Implied Inter-register 1 2 TAX NOP has no side effects. Flag-manipulations like CLC, and SECCLV are used when their effects are desired.
Implied Stack push 1 3 PHA PHP is only paired with PLP.
Implied Stack pop 1 4 PLA
Implied Return 1 6 RTS Used indirectly when paired with JSR. Similarly for RTI.
Immediate 2 2 CMP #$C5 Includes instructions like LDA, LDX and LDY. Other ALU instructions are used in more complex situations.
Relative Branch 2 2—4 BCC *+2 Branch takes 3 cycles when taken, 2 otherwise. A page crossing adds +1 cycle when branch is taken, but because of difficulties setting that up, we don't use it.
Zeropage Read, write 2 3 LDA $A5
Zeropage RMW 2 5 INC @zptemp Writing to zeropage is only permitted when @zptemp is available. Technically we could save @zptemp into register and restore at end, but it is bytewise inferior to other techniques.
Zeropage indexed Read, write 2 4 LDA $EA,X Inferior to 2 × NOP, but useful for hiding additional code to be executed in a loop.
Zeropage indexed RMW 2 6 INC @zptemp,X Only doable when X is known to be 0, or when entire zeropage can be clobbered.
Indexed indirect Read, write 2 6 STA (@ptrtemp,X) Only doable when X is known to be 0.
Indexed indirect RMW 2 8 SLO (@ptrtemp,X) The most cost-effective instruction. Only doable when X is known to be 0, lest we write to a random address. All instructions in this category are unofficial.
Indirect indexed Read 2 5—6 LDA (@ptrtemp),Y Never used by this code.
Indirect indexed Write 2 6 STA (@ptrtemp),Y Only doable when Y is known to be 0.
Indirect indexed RMW 2 8 SLO (@ptrtemp),Y All instructions in this category are unofficial.
Absolute Jump 3 3 JMP *+3
Absolute Read, write 3 4 LDA $2808 Inferior to 2 × NOP, but can be used carefully to hide additional code to be executed in a loop.
Absolute RMW 3 6 INC $4018 Inferior to 3 × NOP.
Absolute indexed Read 3 4—5 LDA $0200,X Inferior to shorter alternatives.
Absolute indexed Write 3 5 STA $0200,X Inferior to shorter alternatives.
Absolute indexed RMW 3 7 INC $4018,X Only doable when writing into the given address is harmless considering the possible values of X.
Absolute indirect Jump 3 5 JMP (@ptrtemp) Inferior to shorter alternatives.



2 cycles

1 bytes
EA       NOP
No requirements
  • All instructions cost at least 2 cycles. There is no way to do 1 cycle of delay (though −1 cycles may sometimes appear in branch cost calculations).


3 cycles

2 bytes
C5 C5    CMP $C5
Clobbers Z&N, and C
24 24    BIT $24
Clobbers Z&N, and V
A5 A5    LDA $A5
Clobbers A, and Z&N
A6 A6    LDX $A6
Clobbers X, and Z&N
A4 A4    LDY $A4
Clobbers Y, and Z&N
3 bytes
4C xx xx JMP *+3
No requirements
  • Not relocatable means that the target address is hardcoded into the code. In ROM hacking, it sometimes makes sense to move code blobs around, and a hardcoded address makes it difficult to relocate the code. This restriction does not apply to branches, which use relative addressing. It is also assumed to not apply to JSR instructions, as chances are the JSR target is outside the code being relocated.


4 cycles

2 bytes
EA   ... NOP      × 2
No requirements
  • zp-indexed modes such as LDA $00,X also do 4 cycles, but having side effects, these two-byte instructions are inferior to a simple 2 × NOP.
  • There is also an unofficial opcode NOP $00,X (34 00), but there is no reason to use this instruction when the official equivalent has the same performance.


5 cycles

3 bytes
18       CLC
90 00    BCC *+2
Clobbers C
B8       CLV
50 00    BVC *+2
Clobbers V
EA       NOP
A5 A5    LDA $A5
Clobbers A, and Z&N
EA       NOP
A6 A6    LDX $A6
Clobbers X, and Z&N
EA       NOP
A4 A4    LDY $A4
Clobbers Y, and Z&N
4 bytes
EA       NOP
4C xx xx JMP *+3
No requirements
  • abs-indexed modes such as LDA $1234,X cause 4 or 5 cycles of delay, depending whether a page wrap occurred. Because you need extra setup code to make sure that a wrap does occur, you do not see this mode in these samples, outside situations where circumstances permit.


6 cycles

3 bytes
EA   ... NOP      × 3
No requirements
  • zp-indexed RMW instructions such as INC @zptemp,X do 6 cycles. Unless we know the value of X, it might write into any address between $00-$FF. This option is only useful if the entire range of $00-$FF is free for clobbering with random data, or if X has a known value.
  • ix instructions like LDA ($00,X) do 6 cycles, but the value of X decides where a pointer is read from, and said pointer can point anywhere. We only do that when the value of X is known.
  • iy instructions like LDA ($00),Y also do 5-6 cycles, but in addition to the note above, we cannot predict whether a wrap occurs or not. So we don't use this mode.
  • Absolute RMW instructions like INC $4018 do 6 cycles, but weighing 3 bytes with side-effects it would be inferior to 3 × NOP.


7 cycles

2 bytes
08       PHP
28       PLP
No requirements
  • PHP-PLP is very efficient for 7 cycles of delay, but it does modify stack contents. S register remains unchanged though.
  • PLA-PHA does not overwrite any bytes in stack. It just writes back the same byte. But it does clobber A and Z+N. It is not interrupt-unsafe either: If an interrupt happens, the stack byte does get temporarily clobbered, but the value is still in A when the interrupt exits, and gets written back in stack.
  • abs-indexed RMW instructions such as INC abs,X do 7 cycles. We only do this when either we know the value of X (for instance, INC $4018,X is safe when X is 0—7</code>, or when the entire 256-byte page can be safely overwritten with random data.


8 cycles

4 bytes
EA   ... NOP      × 4
No requirements
  • Unofficial ix and iy RMW instructions such as SLO ($00,X) or SLO ($00),Y would do 8 cycles for 2 bytes of code. We only do that if we know X or Y to be zero, and we have a known pointer to safely rewritable data.


9 cycles

3 bytes
EA       NOP
08       PHP
28       PLP
No requirements
  • Jumping into the middle of another instruction and thereby reusing code is a very efficient way of reducing code size. Note that all code samples using branches on this page require that no page wrap occurs.


10 cycles

4 bytes
08       PHP
C5 C5    CMP $C5
28       PLP
No requirements
  • The ROL-ROR sequence preserves the original value of the memory address. Carry is also preserved.


11 cycles

4 bytes
EA   ... NOP      × 2
08       PHP
28       PLP
No requirements


12 cycles

3 bytes
20 xx xx JSR @rts12
Requires @rts12
4 bytes
36 36    ROL $36,X
76 36    ROR $36,X
Clobbers Z&N
5 bytes
08       PHP
18       CLC
90 00    BCC *+2
28       PLP
No requirements
  • JSR-RTS causes 12 cycles of delay. But it does write a function return address in the stack, which may be unwanted in some applications. S is not modified.
  • Again, ROL-ROR does not have side effects (as long as an interrupt does not happen in the middle), except for Z+N.


13 cycles

5 bytes
EA   ... NOP      × 3
08       PHP
28       PLP
No requirements


14 cycles

4 bytes
08       PHP       \ × 2
28       PLP       /
No requirements


15 cycles

5 bytes
08       PHP
BA       TSX
28       PLP
9A       TXS
28       PLP
Clobbers X
C5 C5    CMP $C5
20 xx xx JSR @rts12
Clobbers Z&N, and C; and requires @rts12
24 24    BIT $24
20 xx xx JSR @rts12
Clobbers Z&N, and V; and requires @rts12
A5 A5    LDA $A5
20 xx xx JSR @rts12
Clobbers A, and Z&N; and requires @rts12
A4 A4    LDY $A4
20 xx xx JSR @rts12
Clobbers Y, and Z&N; and requires @rts12
6 bytes
08       PHP
28       PLP
EA   ... NOP      × 4
No requirements


16 cycles

5 bytes
EA       NOP
08       PHP       \ × 2
28       PLP       /
No requirements


17 cycles

6 bytes
08       PHP
48       PHA
A5 A5    LDA $A5
68       PLA
28       PLP
No requirements


18 cycles

6 bytes
EA   ... NOP      × 2
08       PHP       \ × 2
28       PLP       /
No requirements


19 cycles

5 bytes
08       PHP
28       PLP
20 xx xx JSR @rts12
Requires @rts12
6 bytes
08       PHP
36 36    ROL $36,X
76 36    ROR $36,X
28       PLP
No requirements


20 cycles

5 bytes
A9 2A    LDA #$2A ;hides 'ROL A'
38       SEC
10 FC    BPL *-2
Clobbers A, Z&N, and C
7 bytes
EA   ... NOP      × 3
08       PHP       \ × 2
28       PLP       /
No requirements


21 cycles

5 bytes
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
90 FD    BCC *-1
Clobbers A, Z&N, and C
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
6 bytes
08       PHP       \ × 3
28       PLP       /
No requirements


22 cycles

6 bytes
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
38       SEC
10 FC    BPL *-2
Clobbers A, Z&N, and C
A2 02    LDX #2
EA       NOP
CA       DEX
10 FC    BPL *-2
Clobbers X, and Z&N
A0 03    LDY #3
EA       NOP
88       DEY
D0 FC    BNE *-2
Clobbers Y, and Z&N
7 bytes
08       PHP
BA       TSX
08       PHP
28   ... PLP      × 2
9A       TXS
28       PLP
Clobbers X
08       PHP
C5 C5    CMP $C5
28       PLP
20 xx xx JSR @rts12
Requires @rts12
8 bytes
08       PHP       \ × 2
28       PLP       /
EA   ... NOP      × 4
No requirements


23 cycles

6 bytes
18   ... CLC      × 2
A9 2A    LDA #$2A ;hides 'ROL A'
90 FD    BCC *-1
Clobbers A, Z&N, and C
EA       NOP
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
EA       NOP
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
7 bytes
EA       NOP
08       PHP       \ × 3
28       PLP       /
No requirements


24 cycles

4 bytes
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
Clobbers A, Z&N, and C
6 bytes
20 xx xx JSR @rts12× 2
Requires @rts12
7 bytes
A6 A6    LDX $A6
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
A4 A4    LDY $A4
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
8 bytes
08       PHP
C5 C5    CMP $C5
28       PLP       \ × 2
08       PHP       /
28       PLP
No requirements


25 cycles

7 bytes
98       TYA
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
A8       TAY
Clobbers A, and Z&N
EA   ... NOP      × 2
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
EA   ... NOP      × 2
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
8 bytes
EA   ... NOP      × 2
08       PHP       \ × 3
28       PLP       /
No requirements


26 cycles

5 bytes
18       CLC
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
Clobbers A, Z&N, and C
A2 04    LDX #4
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
7 bytes
EA       NOP
20 xx xx JSR @rts12× 2
Requires @rts12
8 bytes
08       PHP
48       PHA
36 36    ROL $36,X
76 36    ROR $36,X
68       PLA
28       PLP
No requirements


27 cycles

6 bytes
A5 A5    LDA $A5
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
Clobbers A, Z&N, and C
7 bytes
48       PHA
A9 2A    LDA #$2A ;hides 'ROL A'
38       SEC
10 FC    BPL *-2
68       PLA
Clobbers Z&N, and C
08       PHP
A9 2A    LDA #$2A ;hides 'ROL A'
38       SEC
10 FC    BPL *-2
28       PLP
Clobbers A
24 2C    BIT <$2C ;hides 'BIT $FDA2'
A2 FD    LDX #253
E8       INX
D0 FA    BNE *-4
Clobbers X, Z&N, and V
24 2C    BIT <$2C ;hides 'BIT $FDA0'
A0 FD    LDY #253
C8       INY
D0 FA    BNE *-4
Clobbers Y, Z&N, and V
A4 AC    LDY <$AC ;hides 'LDY $82A2'
A2 82    LDX #130
CA       DEX
30 FA    BMI *-4
Clobbers X, Y, and Z&N
8 bytes
EA   ... NOP      × 3
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
EA   ... NOP      × 3
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
24 24    BIT $24
20 xx xx JSR @rts12× 2
Clobbers Z&N, and V; and requires @rts12
20 xx xx JSR @rts12
08       PHP
BA       TSX
28       PLP
9A       TXS
28       PLP
Clobbers X; and requires @rts12
9 bytes
EA   ... NOP      × 3
08       PHP       \ × 3
28       PLP       /
No requirements


28 cycles

6 bytes
38   ... SEC      × 2
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
Clobbers A, Z&N, and C
EA       NOP
A2 04    LDX #4
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
EA       NOP
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
7 bytes
48       PHA
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
90 FD    BCC *-1
68       PLA
Clobbers Z&N, and C
08       PHP
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
90 FD    BCC *-1
28       PLP
Clobbers A
08       PHP
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
08       PHP
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
8 bytes
08       PHP       \ × 4
28       PLP       /
No requirements


29 cycles

6 bytes
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
EA       NOP
90 FC    BCC *-2
Clobbers A, Z&N, and C
A2 04    LDX #4
EA       NOP
CA       DEX
D0 FC    BNE *-2
Clobbers X, and Z&N
A0 04    LDY #4
EA       NOP
88       DEY
D0 FC    BNE *-2
Clobbers Y, and Z&N
8 bytes
48       PHA
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
38       SEC
10 FC    BPL *-2
68       PLA
Clobbers Z&N, and C
08       PHP
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
38       SEC
10 FC    BPL *-2
28       PLP
Clobbers A
08       PHP
A2 02    LDX #2
EA       NOP
CA       DEX
10 FC    BPL *-2
28       PLP
Clobbers X
08       PHP
A0 03    LDY #3
EA       NOP
88       DEY
D0 FC    BNE *-2
28       PLP
Clobbers Y
9 bytes
08       PHP
28       PLP
08       PHP
C5 C5    CMP $C5
28       PLP
20 xx xx JSR @rts12
Requires @rts12
10 bytes
08       PHP
C5 C5    CMP $C5
28       PLP
08       PHP
36 36    ROL $36,X
76 36    ROR $36,X
28       PLP
No requirements


30 cycles

7 bytes
98       TYA
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
A8       TAY
Clobbers A, and Z&N
EA   ... NOP      × 2
A2 04    LDX #4
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
EA   ... NOP      × 2
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
8 bytes
48       PHA
18   ... CLC      × 2
A9 2A    LDA #$2A ;hides 'ROL A'
90 FD    BCC *-1
68       PLA
Clobbers Z&N, and C
08       PHP
18   ... CLC      × 2
A9 2A    LDA #$2A ;hides 'ROL A'
90 FD    BCC *-1
28       PLP
Clobbers A
EA       NOP
08       PHP
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
EA       NOP
08       PHP
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
9 bytes
08       PHP
48       PHA
18       CLC
A9 6A    LDA #$6A ;hides 'ROR A'
90 FD    BCC *-1
68       PLA
28       PLP
No requirements


31 cycles

5 bytes
18       CLC
A9 0A    LDA #$0A ;hides 'ASL A'
90 FD    BCC *-1
Clobbers A, Z&N, and C
A2 05    LDX #5
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
A0 06    LDY #6
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
6 bytes
48       PHA
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
68       PLA
Clobbers Z&N, and C
08       PHP
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
28       PLP
Clobbers A
8 bytes
08       PHP
28       PLP
20 xx xx JSR @rts12× 2
Requires @rts12
9 bytes
08       PHP
A6 A6    LDX $A6
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
08       PHP
A4 A4    LDY $A4
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
10 bytes
08       PHP
36 36    ROL $36,X \ × 2
76 36    ROR $36,X /
28       PLP
No requirements


32 cycles

6 bytes
A2 05    LDX #5 ;hides 'ORA zp'
CA       DEX ;first loop only
CA       DEX
D0 FB    BNE *-3
Clobbers A, X, and Z&N
A0 05    LDY #5 ;hides 'ORA zp'
88       DEY ;first loop only
88       DEY
D0 FB    BNE *-3
Clobbers A, Y, and Z&N
7 bytes
A9 2A    LDA #$2A ;hides 'ROL A'
EA   ... NOP      × 3
10 FA    BPL *-4
Clobbers A, Z&N, and C
8 bytes
EA       NOP
98       TYA
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
A8       TAY
Clobbers A, and Z&N
A6 A6    LDX $A6
A2 04    LDX #4
EA       NOP
CA       DEX
D0 FC    BNE *-2
Clobbers X, and Z&N
A4 A4    LDY $A4
A0 04    LDY #4
EA       NOP
88       DEY
D0 FC    BNE *-2
Clobbers Y, and Z&N
9 bytes
48       PHA
98       TYA
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
A8       TAY
68       PLA
Clobbers Z&N
08       PHP
98       TYA
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
A8       TAY
28       PLP
Clobbers A
EA   ... NOP      × 2
08       PHP
A2 04    LDX #4
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
EA   ... NOP      × 2
08       PHP
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
10 bytes
08       PHP
48       PHA
18   ... CLC      × 2
A9 6A    LDA #$6A ;hides 'ROR A'
90 FD    BCC *-1
68       PLA
28       PLP
No requirements


33 cycles

6 bytes
18   ... CLC      × 2
A9 0A    LDA #$0A ;hides 'ASL A'
90 FD    BCC *-1
Clobbers A, Z&N, and C
EA       NOP
A2 05    LDX #5
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
EA       NOP
A0 06    LDY #6
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
7 bytes
48       PHA
18       CLC
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
68       PLA
Clobbers Z&N, and C
08       PHP
18       CLC
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
28       PLP
Clobbers A
08       PHP
A2 04    LDX #4
CA       DEX
10 FD    BPL *-1
28       PLP
Clobbers X
08       PHP
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
9 bytes
EA       NOP
08       PHP
28       PLP
20 xx xx JSR @rts12× 2
Requires @rts12
10 bytes
08       PHP       \ × 2
28       PLP       /
08       PHP
36 36    ROL $36,X
76 36    ROR $36,X
28       PLP
No requirements


34 cycles

5 bytes
A9 0A    LDA #$0A ;hides 'ASL A'
18       CLC
10 FC    BPL *-2
Clobbers A, Z&N, and C
A0 88    LDY #136 ;hides 'DEY'
88       DEY
30 FC    BMI *-2
Clobbers Y, and Z&N
7 bytes
A6 A6    LDX $A6
A2 05    LDX #5
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
8 bytes
C5 C5    CMP $C5
48       PHA
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
68       PLA
Clobbers Z&N, and C
08       PHP
A5 A5    LDA $A5
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
28       PLP
Clobbers A
9 bytes
08       PHP
48       PHA
A9 2A    LDA #$2A ;hides 'ROL A'
38       SEC
10 FC    BPL *-2
68       PLA
28       PLP
No requirements


35 cycles

6 bytes
A9 2A    LDA #$2A ;hides 'ROL A'
08       PHP
28       PLP
10 FB    BPL *-3
Clobbers A, Z&N, and C
A2 F8    LDX #248 ;hides 'SED'
E8   ... INX      × 2
D0 FB    BNE *-3
Clobbers X, Z&N, and D
A0 88    LDY #136 ;hides 'DEY'
88   ... DEY      × 2
30 FB    BMI *-3
Clobbers Y, and Z&N
7 bytes
98       TYA
A0 06    LDY #6
88       DEY
D0 FD    BNE *-1
A8       TAY
Clobbers A, and Z&N
EA   ... NOP      × 2
A2 05    LDX #5
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
8 bytes
48       PHA
38   ... SEC      × 2
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
68       PLA
Clobbers Z&N, and C
08       PHP
38   ... SEC      × 2
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
28       PLP
Clobbers A
EA       NOP
08       PHP
A2 04    LDX #4
CA       DEX
10 FD    BPL *-1
28       PLP
Clobbers X
EA       NOP
08       PHP
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
9 bytes
08       PHP
48       PHA
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
90 FD    BCC *-1
68       PLA
28       PLP
No requirements


36 cycles

5 bytes
A9 E9    LDA #$E9 ;hides 'SBC #$2A'
2A       ROL A ;first loop only
B0 FC    BCS *-2
Clobbers A, Z&N, C, and V
A2 07    LDX #7
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
Clobbers Y, and Z&N
6 bytes
38       SEC
A9 0A    LDA #$0A ;hides 'ASL A'
38       SEC
10 FC    BPL *-2
Clobbers A, Z&N, and C
8 bytes
48       PHA
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
EA       NOP
90 FC    BCC *-2
68       PLA
Clobbers Z&N, and C
08       PHP
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
EA       NOP
90 FC    BCC *-2
28       PLP
Clobbers A
08       PHP
A2 04    LDX #4
EA       NOP
CA       DEX
D0 FC    BNE *-2
28       PLP
Clobbers X
08       PHP
A0 04    LDY #4
EA       NOP
88       DEY
D0 FC    BNE *-2
28       PLP
Clobbers Y
9 bytes
20 xx xx JSR @rts12× 3
Requires @rts12
10 bytes
08       PHP
48       PHA
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
38       SEC
10 FC    BPL *-2
68       PLA
28       PLP
No requirements


37 cycles

7 bytes
A5 A5    LDA $A5
A9 0A    LDA #$0A ;hides 'ASL A'
18       CLC
10 FC    BPL *-2
Clobbers A, Z&N, and C
A2 04    LDX #4
EA   ... NOP      × 2
CA       DEX
D0 FB    BNE *-3
Clobbers X, and Z&N
A0 04    LDY #4
EA   ... NOP      × 2
88       DEY
D0 FB    BNE *-3
Clobbers Y, and Z&N
8 bytes
EA       NOP
98       TYA
A0 06    LDY #6
88       DEY
D0 FD    BNE *-1
A8       TAY
Clobbers A, and Z&N
9 bytes
48       PHA
98       TYA
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
A8       TAY
68       PLA
Clobbers Z&N
08       PHP
98       TYA
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
A8       TAY
28       PLP
Clobbers A
EA   ... NOP      × 2
08       PHP
A2 04    LDX #4
CA       DEX
10 FD    BPL *-1
28       PLP
Clobbers X
EA   ... NOP      × 2
08       PHP
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
10 bytes
08       PHP
48       PHA
18   ... CLC      × 2
A9 2A    LDA #$2A ;hides 'ROL A'
90 FD    BCC *-1
68       PLA
28       PLP
No requirements


38 cycles

6 bytes
38       SEC
A9 69    LDA #$69 ;hides 'ADC #$EA'
EA       NOP ;first loop only
B0 FC    BCS *-2
Clobbers A, Z&N, C, and V
EA       NOP
A2 07    LDX #7
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
EA       NOP
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
Clobbers Y, and Z&N
7 bytes
48       PHA
18       CLC
A9 0A    LDA #$0A ;hides 'ASL A'
90 FD    BCC *-1
68       PLA
Clobbers Z&N, and C
08       PHP
18       CLC
A9 0A    LDA #$0A ;hides 'ASL A'
90 FD    BCC *-1
28       PLP
Clobbers A
08       PHP
A2 05    LDX #5
CA       DEX
10 FD    BPL *-1
28       PLP
Clobbers X
08       PHP
A0 06    LDY #6
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
8 bytes
08       PHP
48       PHA
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
68       PLA
28       PLP
No requirements


39 cycles

4 bytes
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
Clobbers A, Z&N, and C
7 bytes
A6 A6    LDX $A6
A2 07    LDX #7
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
A4 A4    LDY $A4
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
Clobbers Y, and Z&N
8 bytes
98       TYA
A0 88    LDY #136 ;hides 'DEY'
88   ... DEY      × 2
30 FB    BMI *-3
A8       TAY
Clobbers A, and Z&N
08       PHP
A2 05    LDX #5 ;hides 'ORA zp'
CA       DEX ;first loop only
CA       DEX
D0 FB    BNE *-3
28       PLP
Clobbers A, and X
08       PHP
A0 05    LDY #5 ;hides 'ORA zp'
88       DEY ;first loop only
88       DEY
D0 FB    BNE *-3
28       PLP
Clobbers A, and Y
9 bytes
48       PHA
A9 2A    LDA #$2A ;hides 'ROL A'
EA   ... NOP      × 3
10 FA    BPL *-4
68       PLA
Clobbers Z&N, and C
08       PHP
A9 2A    LDA #$2A ;hides 'ROL A'
EA   ... NOP      × 3
10 FA    BPL *-4
28       PLP
Clobbers A
10 bytes
EA       NOP
48       PHA
98       TYA
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
A8       TAY
68       PLA
Clobbers Z&N
08       PHP
A6 A6    LDX $A6
A2 04    LDX #4
EA       NOP
CA       DEX
D0 FC    BNE *-2
28       PLP
Clobbers X
08       PHP
A4 A4    LDY $A4
A0 04    LDY #4
EA       NOP
88       DEY
D0 FC    BNE *-2
28       PLP
Clobbers Y
11 bytes
08       PHP
48       PHA
98       TYA
A0 04    LDY #4
88       DEY
D0 FD    BNE *-1
A8       TAY
68       PLA
28       PLP
No requirements


40 cycles

6 bytes
A2 05    LDX #5 ;hides 'ORA zp'
EA       NOP
CA       DEX
D0 FB    BNE *-3
Clobbers A, X, and Z&N
A0 05    LDY #5 ;hides 'ORA zp'
EA       NOP
88       DEY
D0 FB    BNE *-3
Clobbers A, Y, and Z&N
7 bytes
98       TYA
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
A8       TAY
Clobbers A, and Z&N
EA   ... NOP      × 2
A2 07    LDX #7
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
EA   ... NOP      × 2
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
Clobbers Y, and Z&N
8 bytes
48       PHA
18   ... CLC      × 2
A9 0A    LDA #$0A ;hides 'ASL A'
90 FD    BCC *-1
68       PLA
Clobbers Z&N, and C
08       PHP
18   ... CLC      × 2
A9 0A    LDA #$0A ;hides 'ASL A'
90 FD    BCC *-1
28       PLP
Clobbers A
EA       NOP
08       PHP
A2 05    LDX #5
CA       DEX
10 FD    BPL *-1
28       PLP
Clobbers X
EA       NOP
08       PHP
A0 06    LDY #6
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
9 bytes
08       PHP
48       PHA
18       CLC
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
68       PLA
28       PLP
No requirements


41 cycles

5 bytes
38       SEC
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
Clobbers A, Z&N, and C
A2 08    LDX #8
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
A0 08    LDY #8
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
7 bytes
48       PHA
A9 0A    LDA #$0A ;hides 'ASL A'
18       CLC
10 FC    BPL *-2
68       PLA
Clobbers Z&N, and C
08       PHP
A9 0A    LDA #$0A ;hides 'ASL A'
18       CLC
10 FC    BPL *-2
28       PLP
Clobbers A
08       PHP
A0 88    LDY #136 ;hides 'DEY'
88       DEY
30 FC    BMI *-2
28       PLP
Clobbers Y
9 bytes
08       PHP
A6 A6    LDX $A6
A2 05    LDX #5
CA       DEX
10 FD    BPL *-1
28       PLP
Clobbers X
10 bytes
08       PHP
48       PHA
A5 A5    LDA $A5
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
68       PLA
28       PLP
No requirements


42 cycles

6 bytes
A5 A5    LDA $A5
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
Clobbers A, Z&N, and C
7 bytes
EA       NOP
A2 05    LDX #5 ;hides 'ORA zp'
EA       NOP
CA       DEX
D0 FB    BNE *-3
Clobbers A, X, and Z&N
EA       NOP
A0 05    LDY #5 ;hides 'ORA zp'
EA       NOP
88       DEY
D0 FB    BNE *-3
Clobbers A, Y, and Z&N
8 bytes
48       PHA
A9 2A    LDA #$2A ;hides 'ROL A'
08       PHP
28       PLP
10 FB    BPL *-3
68       PLA
Clobbers Z&N, and C
08       PHP
A9 2A    LDA #$2A ;hides 'ROL A'
08       PHP
28       PLP
10 FB    BPL *-3
28       PLP
Clobbers A
08       PHP
A2 F8    LDX #248 ;hides 'SED'
E8   ... INX      × 2
D0 FB    BNE *-3
28       PLP
Clobbers X
08       PHP
A0 88    LDY #136 ;hides 'DEY'
88   ... DEY      × 2
30 FB    BMI *-3
28       PLP
Clobbers Y
9 bytes
48       PHA
98       TYA
A0 06    LDY #6
88       DEY
D0 FD    BNE *-1
A8       TAY
68       PLA
Clobbers Z&N
10 bytes
08       PHP
48       PHA
38   ... SEC      × 2
A9 0A    LDA #$0A ;hides 'ASL A'
10 FD    BPL *-1
68       PLA
28       PLP
No requirements


43 cycles

6 bytes
38   ... SEC      × 2
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
Clobbers A, Z&N, and C
A2 05    LDX #5
EA       NOP
CA       DEX
10 FC    BPL *-2
Clobbers X, and Z&N
A0 06    LDY #6
EA       NOP
88       DEY
D0 FC    BNE *-2
Clobbers Y, and Z&N
7 bytes
48       PHA
A9 E9    LDA #$E9 ;hides 'SBC #$2A'
2A       ROL A ;first loop only
B0 FC    BCS *-2
68       PLA
Clobbers Z&N, C, and V
08       PHP
A9 E9    LDA #$E9 ;hides 'SBC #$2A'
2A       ROL A ;first loop only
B0 FC    BCS *-2
28       PLP
Clobbers A
08       PHP
A2 07    LDX #7
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
08       PHP
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
28       PLP
Clobbers Y
8 bytes
48       PHA
38       SEC
A9 0A    LDA #$0A ;hides 'ASL A'
38       SEC
10 FC    BPL *-2
68       PLA
Clobbers Z&N, and C
10 bytes
08       PHP
48       PHA
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
EA       NOP
90 FC    BCC *-2
68       PLA
28       PLP
No requirements


44 cycles

6 bytes
A9 0A    LDA #$0A ;hides 'ASL A'
EA   ... NOP      × 2
10 FB    BPL *-3
Clobbers A, Z&N, and C
A0 88    LDY #136 ;hides 'DEY'
EA       NOP
88       DEY
30 FB    BMI *-3
Clobbers Y, and Z&N
7 bytes
A6 A6    LDX $A6
A2 08    LDX #8
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
9 bytes
C5 C5    CMP $C5
48       PHA
A9 0A    LDA #$0A ;hides 'ASL A'
18       CLC
10 FC    BPL *-2
68       PLA
Clobbers Z&N, and C
08       PHP
A5 A5    LDA $A5
A9 0A    LDA #$0A ;hides 'ASL A'
18       CLC
10 FC    BPL *-2
28       PLP
Clobbers A
08       PHP
A2 04    LDX #4
EA   ... NOP      × 2
CA       DEX
D0 FB    BNE *-3
28       PLP
Clobbers X
08       PHP
A0 04    LDY #4
EA   ... NOP      × 2
88       DEY
D0 FB    BNE *-3
28       PLP
Clobbers Y
10 bytes
EA       NOP
48       PHA
98       TYA
A0 06    LDY #6
88       DEY
D0 FD    BNE *-1
A8       TAY
68       PLA
Clobbers Z&N
11 bytes
08       PHP
48       PHA
98       TYA
A0 05    LDY #5
88       DEY
D0 FD    BNE *-1
A8       TAY
68       PLA
28       PLP
No requirements


45 cycles

7 bytes
98       TYA
A0 08    LDY #8
88       DEY
D0 FD    BNE *-1
A8       TAY
Clobbers A, and Z&N
EA   ... NOP      × 2
A2 08    LDX #8
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
EA   ... NOP      × 2
A0 08    LDY #8
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
8 bytes
48       PHA
38       SEC
A9 69    LDA #$69 ;hides 'ADC #$EA'
EA       NOP ;first loop only
B0 FC    BCS *-2
68       PLA
Clobbers Z&N, C, and V
08       PHP
38       SEC
A9 69    LDA #$69 ;hides 'ADC #$EA'
EA       NOP ;first loop only
B0 FC    BCS *-2
28       PLP
Clobbers A
EA       NOP
08       PHP
A2 07    LDX #7
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
EA       NOP
08       PHP
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
28       PLP
Clobbers Y
9 bytes
08       PHP
48       PHA
18       CLC
A9 0A    LDA #$0A ;hides 'ASL A'
90 FD    BCC *-1
68       PLA
28       PLP
No requirements


46 cycles

5 bytes
A2 08    LDX #8
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
A0 09    LDY #9
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
6 bytes
48       PHA
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
68       PLA
Clobbers Z&N, and C
08       PHP
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
28       PLP
Clobbers A
9 bytes
08       PHP
A6 A6    LDX $A6
A2 07    LDX #7
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
08       PHP
A4 A4    LDY $A4
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
28       PLP
Clobbers Y
10 bytes
48       PHA
98       TYA
A0 88    LDY #136 ;hides 'DEY'
88   ... DEY      × 2
30 FB    BMI *-3
A8       TAY
68       PLA
Clobbers Z&N
11 bytes
08       PHP
48       PHA
A9 2A    LDA #$2A ;hides 'ROL A'
EA   ... NOP      × 3
10 FA    BPL *-4
68       PLA
28       PLP
No requirements


47 cycles

8 bytes
98       TYA
A0 06    LDY #6
EA       NOP
88       DEY
D0 FC    BNE *-2
A8       TAY
Clobbers A, and Z&N
EA   ... NOP      × 3
A2 08    LDX #8
CA       DEX
D0 FD    BNE *-1
Clobbers X, and Z&N
08       PHP
A2 05    LDX #5 ;hides 'ORA zp'
EA       NOP
CA       DEX
D0 FB    BNE *-3
28       PLP
Clobbers A, and X
EA   ... NOP      × 3
A0 08    LDY #8
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
08       PHP
A0 05    LDY #5 ;hides 'ORA zp'
EA       NOP
88       DEY
D0 FB    BNE *-3
28       PLP
Clobbers A, and Y
9 bytes
48       PHA
98       TYA
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
A8       TAY
68       PLA
Clobbers Z&N
08       PHP
98       TYA
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
A8       TAY
28       PLP
Clobbers A
EA   ... NOP      × 2
08       PHP
A2 07    LDX #7
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
EA   ... NOP      × 2
08       PHP
A0 06    LDY #6
88       DEY
10 FD    BPL *-1
28       PLP
Clobbers Y
10 bytes
08       PHP
48       PHA
18   ... CLC      × 2
A9 0A    LDA #$0A ;hides 'ASL A'
90 FD    BCC *-1
68       PLA
28       PLP
No requirements


48 cycles

6 bytes
EA       NOP
A2 08    LDX #8
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
EA       NOP
A0 09    LDY #9
88       DEY
D0 FD    BNE *-1
Clobbers Y, and Z&N
7 bytes
48       PHA
38       SEC
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
68       PLA
Clobbers Z&N, and C
08       PHP
38       SEC
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
28       PLP
Clobbers A
08       PHP
A2 08    LDX #8
CA       DEX
D0 FD    BNE *-1
28       PLP
Clobbers X
08       PHP
A0 08    LDY #8
88       DEY
D0 FD    BNE *-1
28       PLP
Clobbers Y
9 bytes
08       PHP
48       PHA
A9 0A    LDA #$0A ;hides 'ASL A'
18       CLC
10 FC    BPL *-2
68       PLA
28       PLP
No requirements


49 cycles

4 bytes
A0 88    LDY #136 ;hides 'DEY'
30 FD    BMI *-1
Clobbers Y, and Z&N
7 bytes
18       CLC
A9 2A    LDA #$2A ;hides 'ROL A'
08       PHP
28       PLP
90 FB    BCC *-3
Clobbers A, Z&N, and C
A6 A6    LDX $A6
A2 08    LDX #8
CA       DEX
10 FD    BPL *-1
Clobbers X, and Z&N
8 bytes
C5 C5    CMP $C5
48       PHA
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
68       PLA
Clobbers Z&N, and C
08       PHP
A5 A5    LDA $A5
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
28       PLP
Clobbers A
10 bytes
08       PHP
48       PHA
A9 2A    LDA #$2A ;hides 'ROL A'
08       PHP
28       PLP
10 FB    BPL *-3
68       PLA
28       PLP
No requirements


50 cycles

6 bytes
A9 E9    LDA #$E9 ;hides 'SBC #$2A'
2A       ROL A ;first loop only
EA       NOP
B0 FB    BCS *-3
Clobbers A, Z&N, C, and V
A2 07    LDX #7
EA       NOP
CA       DEX
D0 FC    BNE *-2
Clobbers X, and Z&N
A0 06    LDY #6
EA       NOP
88       DEY
10 FC    BPL *-2
Clobbers Y, and Z&N
7 bytes
98       TYA
A0 09    LDY #9
88       DEY
D0 FD    BNE *-1
A8       TAY
Clobbers A, and Z&N
8 bytes
48       PHA
38   ... SEC      × 2
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
68       PLA
Clobbers Z&N, and C
08       PHP
38   ... SEC      × 2
A9 4A    LDA #$4A ;hides 'LSR A'
D0 FD    BNE *-1
28       PLP
Clobbers A
08       PHP
A2 05    LDX #5
EA       NOP
CA       DEX
10 FC    BPL *-2
28       PLP
Clobbers X
08       PHP
A0 06    LDY #6
EA       NOP
88       DEY
D0 FC    BNE *-2
28       PLP
Clobbers Y
9 bytes
08       PHP
48       PHA
A9 E9    LDA #$E9 ;hides 'SBC #$2A'
2A       ROL A ;first loop only
B0 FC    BCS *-2
68       PLA
28       PLP
No requirements


Sanity checks

It is possible to verify on compile time that no page wrap occurs, by replacing all branches with these macros:

.macro branch_check opc, dest
    opc dest
    .assert >* = >(dest), warning, "branch_check: failed, crosses page"
.endmacro
.macro bccnw dest
        branch_check bcc, dest
.endmacro
.macro bcsnw dest
        branch_check bcs, dest
.endmacro
.macro beqnw dest
        branch_check beq, dest
.endmacro
.macro bnenw dest
        branch_check bne, dest
.endmacro
.macro bminw dest
        branch_check bmi, dest
.endmacro
.macro bplnw dest
        branch_check bpl, dest
.endmacro
.macro bvcnw dest
        branch_check bvc, dest
.endmacro
.macro bvsnw dest
        branch_check bvs, dest
.endmacro

See also

  • Cycle counting
  • Delay code for functions that produce runtime-determined amount of delay
  • Bisqwit’s “vending machine” for producing a ca65-compatible delay_n macro for arbitrary number of cycles, with more fine-grained configurable constraints: http://bisqwit.iki.fi/utils/nesdelay.php The samples on this page are excerpts from files generated by this online tool.