1.2.2.5 Example Stimuli Session

This program sets up PORTA as output and PORTB as input, and then loops, reading whatever is present on PINB, increments it by one, and outputs it at PORTA.

reset:
	rjmp start
start:
	ldi  r16, 0xff
	out  DDRA, r16   // PORTA => output
	clr  r0
	out  DDRB, r0    // input <= PORTB
loop:
	in   r0, PINB    // Requires stimuli for any action
	inc  r0
	out  PORTA, r0
	rjmp loop

Without stimuli, this program will read 0 from PINB, and output 1 to PORTA, forever.

Now apply the following stimuli file:

// Example stimuli file, feeds any output on PINA back to PINB.
#10
$repeat 10
	PINB = *PINA
	#10
	$break
$endrep

PINB will now be driven by the output from PORTA every 10^th cycle, and the effect will be directly visible in the I/O view. Thanks to the $break directive inside the loop, the program will stop every 10 cycles without any breakpoint in the program.

The following example is made for ATmega328P but should work with most ATtiny or ATmega devices. This program starts TIMER0 and then enters a loop, constantly adding 1 to the value in PIND and assigning the result to PORTD.

#include <avr/io.h>

int main(void)
{
	DDRD = 0xFF;
	TCCR0B = (1<<CS00);
    while(1)
    {
        PORTD = PIND + 1;
    }
}

When applying the following stimuli, it will create a log file that starts logging the value of PORTD and PIND. After 20 cycles, it changes to logging PIND and TCNT0, and after another 20 cycles, it continues to only log PIND for 60 cycles.

$log PORTD
$log PIND
$startlog mega328p_log_output.stim
#20
$unlog PORTD
$log TCNT0
#20
$unlog TCNT0
#60
$stoplog
$break

This will produce a file called mega328p_log_output.stim with the following content:

#6
PORTD = 0x01
#1
PIND = 0x01
#4
PORTD = 0x02
#1
PIND = 0x02
#4
PORTD = 0x03
#1
PIND = 0x03
#3
TCNT0 = 0x10
TCNT0 = 0x11
#1
TCNT0 = 0x12
#1
PIND = 0x04
TCNT0 = 0x13
#1
TCNT0 = 0x14
#1
TCNT0 = 0x15
#1
TCNT0 = 0x16
#1
TCNT0 = 0x17
#1
PIND = 0x05
TCNT0 = 0x18
#1
...

The following example is made for ATmega328P but should work with most ATtiny or ATmega devices. This program starts TIMER0 in fast PWM mode. The output of the PWM signal on PD6 is controlled by PB0. 1 on PB0 enables PWM output, 0 on PB0 disables it.

#include <avr/io.h>

int main(void)
{
	DDRB = 0x00;
	DDRD = 0xFF;
	PORTD = 0x00;
	OCR0A = 0x20;
	TCCR0A = (1<<COM0A0 | 1<<WGM01 | 1<<WGM00);
	TCCR0B |= (1<<CS00);
    while(1)
    {
		if(PINB & 0x01)
			TCCR0B |= (1<<WGM02);
		else
			TCCR0B &= ~(1<<WGM02);
    }
}

When applying the following stimuli, it will create a log file that starts logging the value of PINB and PIND. After 20 cycles, it also starts to log TCNT0. Five cycles later, it applies a 1 to PB0 to start the PWM output, and another five cycles later, it turns off logging of TCNT0. For the next 200 cycles, the PWM output on PD6 will be logged before it is turned off by setting PB0 to 0. Then it continues for another 200 cycles before it breaks.

$log PINB
$log PIND
$startlog mega328p_log_output.stim
#20
// Log TIMER0 counter
$log TCNT0
#5
// Set pin PB0 to '1', Start PWM output
PINB |= 0x01
#5
// Stop logging TIMER0 counter
$unlog TCNT0
#200
// Set pin PB0 to '0', Stop PWM output
PINB &= 0xFE
#200
$stoplog
$break

This will produce a file called mega328p_log_output.stim with the following content:

#20
TCNT0 = 0x09
TCNT0 = 0x0a
#1
TCNT0 = 0x0b
#1
TCNT0 = 0x0c
#1
TCNT0 = 0x0d
#1
TCNT0 = 0x0e
#1
TCNT0 = 0x0f
#1
PINB = 0x01
TCNT0 = 0x10
#1
TCNT0 = 0x11
#1
TCNT0 = 0x12
#1
TCNT0 = 0x13
#15
PIND = 0x40
#33
PIND = 0x00
#33
PIND = 0x40
#33
PIND = 0x00
#33
PIND = 0x40
#33
PIND = 0x00
#22
PINB = 0x00
#11
PIND = 0x40
#1
PIND = 0x00