Date: Tue, 16 Jul 2002 12:22:58 +0200 From: "Jose M. Alcaide" <jose@we.lc.ehu.es> To: Orion Hodson <orion@FreeBSD.ORG> Cc: multimedia@FreeBSD.ORG Subject: Re: interrupts from pcm(4) while no sound is being played Message-ID: <20020716102258.GC259@v-ger.we.lc.ehu.es> In-Reply-To: <200207151652.g6FGqbb18219@puma.icir.org> References: <20020714224531.GA784@v-ger.we.lc.ehu.es> <200207151652.g6FGqbb18219@puma.icir.org>
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On Mon, Jul 15, 2002 at 09:52:37AM -0700, Orion Hodson wrote: > | Is that the expected pcm(4) behaviour? > > Yes. > > Your application is holding the device open after writing data. By writing > data it starts the dma engine on the card, and as a result interrupts start > being generated by the audio device. With each interrupt, an attempt to pull > data from the s/w buffers is made. Your sound plays out, but then the > application does nothing anything to stop the dma engine (ie close the device > or use trigger ioctl) and so interrupts keep getting generated, the device > underflows, silence is written out. OK, thanks for your clear explanation. > There are quite a few applications where this behaviour is useful, ie games > that want to write sounds periodically and not continuously. And in general > it helps avoid weirdness when audio apps are struggling to get cpu cycles on > heavily loaded systems. My only concern is the possible impact of a high interrupt rate (~705 per second after playing a 44KHz, 16 bit sound) on the system performance. For example, that adds a CPU load of ~1.5% in my laptop (Celeron 433) while esd is holding the audio device open (I configured esd for using -and never freeing- /dev/dsp0.1). Cheers, JMA -- ****** Jose M. Alcaide // jose@we.lc.ehu.es // jmas@FreeBSD.org ****** ** "Beware of Programmers who carry screwdrivers" -- Leonard Brandwein ** To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message
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