wait_api functions

Functions
void	wait_us (int us)
	Generic wait functions. More...
void	wait_ns (unsigned int ns)
	Waits a number of nanoseconds. More...

Detailed Description

Function Documentation

wait_us()

void wait_us

(

int

us

)

Generic wait functions.

These provide simple NOP type wait capabilities.

Example:

#include "mbed.h"
 
// Blinking rate in milliseconds
#define BLINKING_RATE_MS   500
DigitalOut  led(LED2);
InterruptIn button(SW2);
 
void blink_led() {
    led = 1;
    wait_us(BLINKING_RATE_MS * 1000);
    led = 0;
}
 
int main() {
    button.fall(&blink_led);
    while(1) {
        // Do nothing
    }
}

Waits a number of microseconds.

Parameters

us	the whole number of microseconds to wait

Note

This function always spins to get the exact number of microseconds. This will affect power and multithread performance. Therefore, spinning for millisecond wait is not recommended, and ThisThread::sleep_for should be used instead.

You may call this function from ISR context, but large delays may impact system stability - interrupt handlers should take less than 50us.

wait_ns()

void wait_ns

(

unsigned int

ns

)

Waits a number of nanoseconds.

This function spins the CPU to produce a small delay. It should normally only be used for delays of 10us (10000ns) or less. As it is calculated based on the expected execution time of a software loop, it may well run slower than requested based on activity from other threads and interrupts. If greater precision is required, this can be called from inside a critical section.

Parameters

ns	the number of nanoseconds to wait

Note

wait_us() will likely give more precise time than wait_ns for large-enough delays, as it is based on a timer, but its set-up time may be excessive for the smallest microsecond counts, at which point wait_ns() is better.

Any delay larger than a millisecond (1000000ns) is liable to cause overflow in the internal loop calculation. You shouldn't normally be using this for such large delays anyway in real code, but be aware if calibrating. Make repeated calls for longer test runs.

You may call this function from ISR context.