AVR clock implementation

Files
file	clock.c
	This file contains AVR-specific code to implement the Contiki core clock functions.

Functions
void	clock_init (void)
	Start the clock by enabling the timer comparison interrupts. More...
clock_time_t	clock_time (void)
	Return the tick counter. More...
unsigned long	clock_seconds (void)
	Return seconds, default is time since startup. More...
void	clock_set_seconds (unsigned long sec)
	Set seconds, e.g. More...
void	clock_wait (clock_time_t t)
	Wait for a given number of ticks. More...
void	clock_delay_usec (uint16_t dt)
	Delay a given number of microseconds. More...
void	clock_delay_msec (uint16_t howlong)
	Delay up to 65535 milliseconds. More...
void	clock_adjust_ticks (clock_time_t howmany)
	Adjust the system current clock time. More...
void	AVR_OUTPUT_COMPARE_INT (void)
	ISR for the TIMER0 or TIMER2 interrupt as defined in clock-avr.h for the particular MCU.

Variables
static volatile clock_time_t	count
	These routines define the AVR-specific calls declared in /core/sys/clock.h CLOCK_SECOND is the number of ticks per second. More...

Detailed Description

Function Documentation

void clock_adjust_ticks

(

clock_time_t

howmany

)

Adjust the system current clock time.

Parameters

howmany

How many ticks to add

Typically used to add ticks after an MCU sleep clock_seconds will increment if necessary to reflect the tick addition. Leap ticks or seconds can (rarely) be introduced if the ISR is not blocked.

Definition at line 289 of file clock.c.

void clock_delay_msec

(

uint16_t

howlong

)

Delay up to 65535 milliseconds.

Parameters

howlong

How many milliseconds to delay.

Neither interrupts nor the watchdog timer is disabled over the delay. Platforms are not required to implement this call.

Note

This will break for CPUs clocked above 260 MHz.

Definition at line 260 of file clock.c.

void clock_delay_usec

(

uint16_t

dt

)

Delay a given number of microseconds.

Parameters

dt	How many microseconds to delay.

Note

Interrupts could increase the delay by a variable amount.

Definition at line 196 of file clock.c.

void clock_init

(

void

)

Start the clock by enabling the timer comparison interrupts.

Initialize the clock library.

Definition at line 116 of file clock.c.

unsigned long clock_seconds

(

void

)

Return seconds, default is time since startup.

Get the current value of the platform seconds.

The comparison avoids the need to disable clock interrupts for an atomic read of the four-byte variable.

Definition at line 144 of file clock.c.

void clock_set_seconds

(

unsigned long

sec

)

Set seconds, e.g.

Set the value of the platform seconds.

to a standard epoch for an absolute date/time.

Definition at line 157 of file clock.c.

clock_time_t clock_time

(

void

)

Return the tick counter.

Get the current clock time.

When 16 bit it typically wraps every 10 minutes. The comparison avoids the need to disable clock interrupts for an atomic read of the multi-byte variable.

Definition at line 129 of file clock.c.

References count.

void clock_wait

(

clock_time_t

t

)

Wait for a given number of ticks.

Parameters

t	How many ticks.

Definition at line 166 of file clock.c.

References clock_time().

Variable Documentation

volatile clock_time_t count

static

These routines define the AVR-specific calls declared in /core/sys/clock.h CLOCK_SECOND is the number of ticks per second.

It is defined through CONF_CLOCK_SECOND in the contiki-conf.h for each platform. The usual AVR defaults are 128 or 125 ticks per second, counting a prescaled CPU clock using the 8 bit timer0.

clock_time_t is usually declared by the platform as an unsigned 16 bit data type, thus intervals up to 512 or 524 seconds can be measured with ~8 millisecond precision. For longer intervals the 32 bit clock_seconds() is available.

Since a carry to a higer byte can occur during an interrupt, declaring them non-static for direct examination can cause occasional time reversals!

clock-avr.h contains the specific setup code for each mcu.

Definition at line 80 of file clock.c.

Referenced by aes_load_keys(), clock_adjust_ticks(), clock_init(), clock_isr(), clock_time(), lcd_symbol_clr_group(), and lcd_symbol_set_group().