Date: Sun, 13 Jul 1997 06:54:16 -0400 (EDT) From: Peter Dufault <dufault@hda.com> To: ccsanady@friley01.res.iastate.edu (Chris Csanady) Cc: hackers@FreeBSD.ORG Subject: Re: DMA directly to user space? Message-ID: <199707131054.GAA10485@hda.hda.com> In-Reply-To: <199707130702.CAA12323@friley01.res.iastate.edu> from Chris Csanady at "Jul 13, 97 02:02:25 am"
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> The thing is, I am looking for a way to do this without copying any data. > Is this possible? Are there any existing devices that do such things? > DMAing to userspace seems ideal, but I'm not sure how you could ensure > that the memory is aligned and contiguous. Or how to deal with the > user/kernel space boundry crossing. All raw I/O works that way. Handle misaligned memory by faulting, punting the issue back to the application. Basically write a strategy function and hook it in as a raw device and you'll have read and write directly to the user space. Non-contiguous memory must be handled either by the device hardware via some flavor of scatter-gather hardware (hopefully you'll find the device in question already does that) or by allocating contiguous memory. -- Peter Dufault (dufault@hda.com) Realtime development, Machine control, HD Associates, Inc. Safety critical systems, Agency approval
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