The fastest way I know is direct port manipulation like:
void setup() {
DDRB |= _BV(PB0);//PB0 as output
}
void loop() {
if (PINB & _BV(PB3)) {// true if PB3 is HIGH
PORTB |= _BV(PB0); // set output HIGH
delay(500);
PORTB &= ~_BV(PB0); // set output LOW
delay(500);
}
}The modern attinies (MegatinyCore) have DigitalwriteFast and PinmodeFast, that compile to a single instruction, but I never heard of the old Attinies having something similar.
[EDIT]
I did a little test to see how the port manipulation compiles.
I compiled this: ( note: I did not care delay() is not working without setup and loop)
int main(void) {
DDRB |= _BV(PB0);//PB0 as output
while (1) {
if (PINB & _BV(PB3)) {// true if PB3 is HIGH
PORTB |= _BV(PB0); // set output HIGH
delay(500);
PORTB &= ~_BV(PB0); // set output LOW
delay(500);
}
}
}And the port manipulation lines also seem to compile to a single instruction
See lines 30: 36: and 4a: in the compile listing is below:
Disassembly of section .text:
00000000 <__vectors>:
__vectors():
0: 0e c0 rjmp .+28 ; 0x1e <__ctors_end>
2: 15 c0 rjmp .+42 ; 0x2e <__bad_interrupt>
4: 14 c0 rjmp .+40 ; 0x2e <__bad_interrupt>
6: 13 c0 rjmp .+38 ; 0x2e <__bad_interrupt>
8: 12 c0 rjmp .+36 ; 0x2e <__bad_interrupt>
a: 11 c0 rjmp .+34 ; 0x2e <__bad_interrupt>
c: 10 c0 rjmp .+32 ; 0x2e <__bad_interrupt>
e: 0f c0 rjmp .+30 ; 0x2e <__bad_interrupt>
10: 0e c0 rjmp .+28 ; 0x2e <__bad_interrupt>
12: 0d c0 rjmp .+26 ; 0x2e <__bad_interrupt>
14: 0c c0 rjmp .+24 ; 0x2e <__bad_interrupt>
16: 0b c0 rjmp .+22 ; 0x2e <__bad_interrupt>
18: 0a c0 rjmp .+20 ; 0x2e <__bad_interrupt>
1a: 09 c0 rjmp .+18 ; 0x2e <__bad_interrupt>
1c: 08 c0 rjmp .+16 ; 0x2e <__bad_interrupt>
0000001e <__ctors_end>:
__trampolines_start():
1e: 11 24 eor r1, r1
20: 1f be out 0x3f, r1 ; 63
22: cf e5 ldi r28, 0x5F ; 95
24: d1 e0 ldi r29, 0x01 ; 1
26: de bf out 0x3e, r29 ; 62
28: cd bf out 0x3d, r28 ; 61
2a: 02 d0 rcall .+4 ; 0x30 <main>
2c: 19 c0 rjmp .+50 ; 0x60 <_exit>
0000002e <__bad_interrupt>:
__vector_1():
2e: e8 cf rjmp .-48 ; 0x0 <__vectors>
00000030 <main>:
main():
E:\Arduino\arduino-1.8.13 - attinycore\portable\sketchbook\portmanipulationtest/portmanipulationtest.ino:2
int main(void) {
DDRB |= _BV(PB0);//PB0 as output
30: b8 9a sbi 0x17, 0 ; 23
E:\Arduino\arduino-1.8.13 - attinycore\portable\sketchbook\portmanipulationtest/portmanipulationtest.ino:4
while (1) {
if (PINB & _BV(PB3)) {// true if PB3 is HIGH
32: b3 9b sbis 0x16, 3 ; 22
34: fe cf rjmp .-4 ; 0x32 <main+0x2>
E:\Arduino\arduino-1.8.13 - attinycore\portable\sketchbook\portmanipulationtest/portmanipulationtest.ino:5
PORTB |= _BV(PB0); // set output HIGH
36: c0 9a sbi 0x18, 0 ; 24
_delay_ms():
e:\arduino\arduino-1.8.13 - attinycore\hardware\tools\avr\avr\include\util/delay.h:187
#else
//round up by default
__ticks_dc = (uint32_t)(ceil(fabs(__tmp)));
#endif
__builtin_avr_delay_cycles(__ticks_dc);
38: 2f ef ldi r18, 0xFF ; 255
3a: 84 e3 ldi r24, 0x34 ; 52
3c: 9c e0 ldi r25, 0x0C ; 12
3e: 21 50 subi r18, 0x01 ; 1
40: 80 40 sbci r24, 0x00 ; 0
42: 90 40 sbci r25, 0x00 ; 0
44: e1 f7 brne .-8 ; 0x3e <__SP_H__>
46: 00 c0 rjmp .+0 ; 0x48 <__SREG__+0x9>
48: 00 00 nop
main():
E:\Arduino\arduino-1.8.13 - attinycore\portable\sketchbook\portmanipulationtest/portmanipulationtest.ino:7
delay(500);
PORTB &= ~_BV(PB0); // set output LOW
4a: c0 98 cbi 0x18, 0 ; 24
_delay_ms():
e:\arduino\arduino-1.8.13 - attinycore\hardware\tools\avr\avr\include\util/delay.h:187
4c: 2f ef ldi r18, 0xFF ; 255
4e: 84 e3 ldi r24, 0x34 ; 52
50: 9c e0 ldi r25, 0x0C ; 12
52: 21 50 subi r18, 0x01 ; 1
54: 80 40 sbci r24, 0x00 ; 0
56: 90 40 sbci r25, 0x00 ; 0
58: e1 f7 brne .-8 ; 0x52 <__SREG__+0x13>
5a: 00 c0 rjmp .+0 ; 0x5c <__SREG__+0x1d>
5c: 00 00 nop
5e: e9 cf rjmp .-46 ; 0x32 <main+0x2>
00000060 <_exit>:
exit():
/home/jenkins-mingw32/workspace/avr-gcc-staging/label/Ubuntu14.04x64-mingw32/gcc-build/avr/avr25/libgcc/../../../../gcc/libgcc/config/avr/lib1funcs.S:2278
60: f8 94 cli
00000062 <__stop_program>:
__stop_program():
/home/jenkins-mingw32/workspace/avr-gcc-staging/label/Ubuntu14.04x64-mingw32/gcc-build/avr/avr25/libgcc/../../../../gcc/libgcc/config/avr/lib1funcs.S:2280
62: ff cf rjmp .-2 ; 0x62 <__stop_program>