1.\" $NetBSD: delay.9,v 1.8 2021/05/31 12:24:15 simonb Exp $ 2.\" 3.\" Copyright (c) 2002 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Gregory McGarry. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd July 20, 2011 31.Dt DELAY 9 32.Os 33.Sh NAME 34.Nm delay , 35.Nm DELAY 36.Nd microsecond delay 37.Sh SYNOPSIS 38.In sys/param.h 39.Ft void 40.Fn delay "unsigned int us" 41.Ft void 42.Fn DELAY "unsigned int us" 43.Sh DESCRIPTION 44Wait approximately 45.Fa us 46microseconds. 47.Pp 48The delay is implemented as a machine loop, preventing events other than 49interrupt handlers for unmasked interrupts to run. 50.Fn DELAY 51is reentrant (doesn't modify any global kernel or machine state) and is 52safe to use in interrupt or process context. 53.Pp 54For long delays, condition variables 55should be considered, however they can only be used from process context 56and their resolution is limited by the system clock frequency. 57.Sh SEE ALSO 58.Xr condvar 9 , 59.Xr hz 9 , 60.Xr kpause 9 61