Date: Sat, 23 May 1998 17:22:15 +0930 From: Greg Lehey <grog@lemis.com> To: FreeBSD Questions <questions@FreeBSD.ORG> Subject: Re: Questions about Bus Mastering Message-ID: <19980523172215.K317@freebie.lemis.com> In-Reply-To: <19980522154209.A1824@ucb.crimea.ua>; from Ruslan Ermilov on Fri, May 22, 1998 at 03:42:09PM %2B0300 References: <19980522154209.A1824@ucb.crimea.ua>
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On Fri, 22 May 1998 at 15:42:09 +0300, Ruslan Ermilov wrote: > Hi! > > Bus mastering... > > What I know about it? This is the PCI technology similar to DMA channels > on the ISA bus. It allows adapters to control the bus. Thus, they can > deliver their data directly to RAM, minimizing the workload on the CPU. > Am I right? Partially. There are two kinds of DMA, master and slave. In slave DMA, the DMA controller handles the transfer, whereas in master mode the controller board controls the transfer. In both cases, the CPU is only involved for setup. Master mode requires more intelligence on the controller board, of course. It's not specific to PCI. > Questions: > > 1. What existing hardware supports bus mastering: SCSI host > adapters, Adaptec 2900 series, etc. > IDE controllers, Most modern mother boards have bus master DMA IDE ports. The latest is "Ultra DMA", which boasts speeds of up to 33 MB/s. > Network adapters? Sorry, I can't name any. > 2. Does FreeBSD support bus mastering and for which hardware? Yes. It's my understanding that most modern bus master boards will only work in this mode. I don't know of any in which FreeBSD doesn't support it, though in particular with IDE it needs to be turned on (look at the comments in the LINT configuration file). Greg -- See complete headers for address and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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