Date: Wed, 08 Jul 2009 12:30:46 +0200 From: Sebastian Huber <sebastian.huber@embedded-brains.de> To: =?ISO-8859-2?Q?Piotr_Zi=EAcik?= <kosmo@semihalf.com> Cc: Rafal Jaworowski <raj@semihalf.com>, freebsd-arm@freebsd.org, freebsd-usb@freebsd.org, thompsa@freebsd.org Subject: Re: CPU Cache and busdma usage in USB Message-ID: <4A547556.4050801@embedded-brains.de> In-Reply-To: <200907081216.40100.kosmo@semihalf.com> References: <200906231035.43096.kosmo@semihalf.com> <37C51279-42D8-49DE-8249-0DA386EBB062@semihalf.com> <200907081103.45388.hselasky@c2i.net> <200907081216.40100.kosmo@semihalf.com>
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Hi! The general approach for systems with no hardware cache coherence protocol should be: Memory to device DMA transfer of a buffer: 1. write all modified cache lines of the buffer back to memory (cache flush for buffer) 2. start DMA transfer Device to memory DMA transfer of a buffer: 1. invalidate the cache of the buffer, here you have to make sure that this buffer does not share a cache line with other buffers (!) 2. start DMA transfer 3. all accesses to the buffer via the cache must wait until the DMA has finished CU -- Sebastian Huber, Embedded Brains GmbH Address : Obere Lagerstr. 30, D-82178 Puchheim, Germany Phone : +49 89 18 90 80 79-6 Fax : +49 89 18 90 80 79-9 E-Mail : sebastian.huber@embedded-brains.de PGP : Public key available on request Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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