Delay (delay)

Busy-wait delay functions based on the clock source (clocksource), providing nanosecond, microsecond, and millisecond precision delays, suitable for short and precise wait scenarios.

How It Works

The delay functions obtain the current time via ktime_get(), compute the target timeout, then busy-wait poll until the timeout:

void udelay(uint32_t us)
{
    ktime_t timeout = ktime_add_us(ktime_get(), us);
    while(ktime_before(ktime_get(), timeout));
}

All three delay functions share the same implementation, differing only in time unit:

• ndelay() uses ktime_add_ns() to add nanoseconds
• udelay() uses ktime_add_us() to add microseconds
• mdelay() uses ktime_add_ms() to add milliseconds

API

Function	Description
ndelay(ns)	Nanosecond busy-wait delay
udelay(us)	Microsecond busy-wait delay
mdelay(ms)	Millisecond busy-wait delay

Usage Examples

#include <kernel/time/delay.h>

/* Wait 10 microseconds after hardware reset */
udelay(10);

/* I2C timing delay */
ndelay(500);

/* Short wait of 5 milliseconds */
mdelay(5);

Notes

• Delays are busy-waits; the CPU is not released during the wait, making them unsuitable for long waits
• Delay precision depends on the clock source device resolution; nanosecond-level timestamps are obtained via ktime_get()
• For long waits, use the timer system (timer) or thread sleep (xos_thread_msleep)
• Safe to use in interrupt context since no scheduling is involved