Timer Function Library (timer.c)
[Drivers (for AVR peripherals)]

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Detailed Description

 #include "timer.h" 

Overview

This library provides functions for use with the timers internal to the AVR processors. Functions include initialization, set prescaler, calibrated pause function (in milliseconds), attaching and detaching of user functions to interrupts, overflow counters, PWM. Arbitrary frequency generation has been moved to the Pulse Library.

About Timers

The Atmel AVR-series processors each contain at least one hardware timer/counter. Many of the processors contain 2 or 3 timers. Generally speaking, a timer is a hardware counter inside the processor which counts at a rate related to the main CPU clock frequency. Because the counter value increasing (counting up) at a precise rate, we can use it as a timer to create or measure precise delays, schedule events, or generate signals of a certain frequency or pulse-width.

As an example, the ATmega163 processor has 3 timer/counters. Timer0, Timer1, and Timer2 are 8, 16, and 8 bits wide respectively. This means that they overflow, or roll over back to zero, at a count value of 256 for 8bits or 65536 for 16bits. A prescaler is avaiable for each timer, and the prescaler allows you to pre-divide the main CPU clock rate down to a slower speed before feeding it to the counting input of a timer. For example, if the CPU clock frequency is 3.69MHz, and Timer0's prescaler is set to divide-by-8, then Timer0 will "tic" at 3690000/8 = 461250Hz. Because Timer0 is an 8bit timer, it will count to 256 in just 256/461250Hz = 0.555ms. In fact, when it hits 255, it will overflow and start again at zero. In this case, Timer0 will overflow 461250/256 = 1801.76 times per second.

Timer0 can be used a number of ways simultaneously. First, the value of the timer can be read by accessing the CPU register TCNT0. We could, for example, figure out how long it takes to execute a C command by recording the value of TCNT0 before and after execution, then subtract (after-before) = time elapsed. Or we can enable the overflow interrupt which goes off every time T0 overflows and count out longer delays (multiple overflows), or execute a special periodic function at every overflow.

The other timers (Timer1 and Timer2) offer all the abilities of Timer0 and many more features. Both T1 and T2 can operate as general-purpose timers, but T1 has special hardware allowing it to generate PWM signals, while T2 is specially designed to help count out real time (like hours, minutes, seconds). See the Timer/Counter section of the processor datasheet for more info.

Modules
	Timer PWM Commands
Defines
#define	PWM10   WGM10
#define	PWM11   WGM11
#define	TIMER_CLK_STOP   0x00
	Timer Stopped.
#define	TIMER_CLK_DIV1   0x01
	Timer clocked at F_CPU.
#define	TIMER_CLK_DIV8   0x02
	Timer clocked at F_CPU/8.
#define	TIMER_CLK_DIV64   0x03
	Timer clocked at F_CPU/64.
#define	TIMER_CLK_DIV256   0x04
	Timer clocked at F_CPU/256.
#define	TIMER_CLK_DIV1024   0x05
	Timer clocked at F_CPU/1024.
#define	TIMER_CLK_T_FALL   0x06
	Timer clocked at T falling edge.
#define	TIMER_CLK_T_RISE   0x07
	Timer clocked at T rising edge.
#define	TIMER_PRESCALE_MASK   0x07
	Timer Prescaler Bit-Mask.
#define	TIMERRTC_CLK_STOP   0x00
	RTC Timer Stopped.
#define	TIMERRTC_CLK_DIV1   0x01
	RTC Timer clocked at F_CPU.
#define	TIMERRTC_CLK_DIV8   0x02
	RTC Timer clocked at F_CPU/8.
#define	TIMERRTC_CLK_DIV32   0x03
	RTC Timer clocked at F_CPU/32.
#define	TIMERRTC_CLK_DIV64   0x04
	RTC Timer clocked at F_CPU/64.
#define	TIMERRTC_CLK_DIV128   0x05
	RTC Timer clocked at F_CPU/128.
#define	TIMERRTC_CLK_DIV256   0x06
	RTC Timer clocked at F_CPU/256.
#define	TIMERRTC_CLK_DIV1024   0x07
	RTC Timer clocked at F_CPU/1024.
#define	TIMERRTC_PRESCALE_MASK   0x07
	RTC Timer Prescaler Bit-Mask.
#define	TIMER0PRESCALE   TIMER_CLK_DIV8
	timer 0 prescaler default
#define	TIMER1PRESCALE   TIMER_CLK_DIV64
	timer 1 prescaler default
#define	TIMER2PRESCALE   TIMERRTC_CLK_DIV64
	timer 2 prescaler default
#define	TIMER0OVERFLOW_INT   0
#define	TIMER1OVERFLOW_INT   1
#define	TIMER1OUTCOMPAREA_INT   2
#define	TIMER1OUTCOMPAREB_INT   3
#define	TIMER1INPUTCAPTURE_INT   4
#define	TIMER2OVERFLOW_INT   5
#define	TIMER2OUTCOMPARE_INT   6
#define	TIMER_NUM_INTERRUPTS   7
#define	TIMER_INTERRUPT_HANDLER   SIGNAL
#define	delay   delay_us
#define	delay_ms   timerPause
Functions
void	delay_us (unsigned short time_us)
void	timerInit (void)
	initializes timing system (all timers)
void	timer0Init (void)
	initialize timer0
void	timer1Init (void)
	initialize timer1
void	timer0SetPrescaler (u08 prescale)
	set timer0 prescaler
u16	timer0GetPrescaler (void)
	get timer0 prescaler
void	timer1SetPrescaler (u08 prescale)
	set timer1 prescaler
u16	timer1GetPrescaler (void)
	get timer0 prescaler
void	timerAttach (u08 interruptNum, void(*userFunc)(void))
	Attach a user function to a timer interrupt.
void	timerDetach (u08 interruptNum)
	Detach a user function from a timer interrupt.
void	timerPause (unsigned short pause_ms)
void	timer0ClearOverflowCount (void)
	Clear timer0's overflow counter.
long	timer0GetOverflowCount (void)
	read timer0's overflow counter

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Function Documentation

void timerPause (  unsigned short  pause_ms  )

A timer-based delay/pause function Parameters: pause_ms  Number of integer milliseconds to wait. Definition at line 204 of file timer.c.

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