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/*
atmega88_timer16.c
Copyright 2008, 2009 Michel Pollet <buserror@gmail.com>
This file is part of simavr.
simavr is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
simavr is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with simavr. If not, see <http://www.gnu.org/licenses/>.
*/
#include <avr/io.h>
#include <stdio.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
/*
* This demonstrates how to use the avr_mcu_section.h file.
* The macro adds a section to the ELF file with useful
* information for the simulator.
*/
#include "avr_mcu_section.h"
AVR_MCU(F_CPU, "atmega88");
/*
* This small section tells simavr to generate a VCD trace dump with changes to these
* registers.
* Opening it with gtkwave will show you the data being read & written to these
* It also demonstrate how you can use unused pins to generate your own traces, with
* your own events to be displayed.
*
* Here the port B first 2 bits are used to display when a tick occurs, and when a
* TCNT reset occurs.
*/
const struct avr_mmcu_vcd_trace_t _mytrace[] _MMCU_ = {
{ AVR_MCU_VCD_SYMBOL("TCNT1L"), .what = (void*)&TCNT1L, },
{ AVR_MCU_VCD_SYMBOL("TCNT1H"), .what = (void*)&TCNT1H, },
};
AVR_MCU_VCD_PORT_PIN('B', 3, "OC2A");
AVR_MCU_VCD_PORT_PIN('B', 1, "reset_timer");
AVR_MCU_VCD_PORT_PIN('B', 0, "tick");
volatile uint16_t tcnt;
ISR(TIMER2_COMPA_vect) // handler for Output Compare 2 overflow interrupt
{
// this really doesn't no anything but proves a way to wake the main()
// from sleep at regular intervals
PORTB ^= 1;
}
int main()
{
//
// start the 16 bits timer, with default "normal" waveform
// and no interupt enabled. This just increments TCNT1
// at a regular rate
//
// timer prescaler to 64
TCCR1B |= (0<<CS12 | 1<<CS11 | 1<<CS10);
DDRB = 0x0B;
//
// now enable a tick counter
// using an asynchronous mode
//
ASSR |= (1 << AS2); // use "external" 32.7k crystal source
// use CLK/8 prescale value, clear timer/counter on compareA match
// toggle OC2A pin too
TCCR2A = (1 << WGM21) | (1 << COM2A0);
TCCR2B = (2 << CS20); // prescaler
OCR2A = 63; // 64 hz
TIMSK2 |= (1 << OCIE2A);
sei();
int count = 0;
while (count++ < 100) {
// we read TCNT1, which should contain some sort of incrementing value
tcnt = TCNT1; // read it
if (tcnt > 10000) {
TCNT1 = 500; // reset it arbitrarily
PORTB ^= 2; // mark it in the waveform file
}
sleep_cpu(); // this will sleep until a new timer2 tick interrupt occurs
}
// sleeping with interrupt off is interpreted by simavr as "exit please"
cli();
sleep_cpu();
}
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