Date: Sun, 11 Oct 1998 00:45:34 -0400 From: Christopher Masto <chris@netmonger.net> To: hackers@FreeBSD.ORG Subject: Re: Contiguous memory allocation Message-ID: <19981011004534.A1416@netmonger.net> In-Reply-To: <199810100955.RAA15119@spinner.netplex.com.au>; from Peter Wemm on Sat, Oct 10, 1998 at 05:55:35PM %2B0800 References: <361F1F49.6E4F@cs.strath.ac.uk> <199810100955.RAA15119@spinner.netplex.com.au>
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On Sat, Oct 10, 1998 at 05:55:35PM +0800, Peter Wemm wrote:
> Have a look at some code that uses contigmalloc(). It's not particularly
> intuitive, but it does work. Some things that use it are busdma_machdep.c
> and isa.c (the isa dma code).
>
> You can request things like:
>
> Give me 16K of physically contiguous data that is aligned on a 16 byte
> boundary, and is entirely within the same 64K window.
>
> Of course, there are no guarantees that you will be able to get a large
> chunk that is physically contiguous, but you can only try. The VM system
> will try quite hard to make the space for your request, even if it has to
I use said function in a driver (LKM) I wrote for a satellite data
receiver, and it is fairly certain to lock the machine up tight if I
don't start it rather soon after boot time. IANAKH. YMMV.
#define BUFFER_SIZE 32768
/* Allocate memory for a buffer */
dma_buflen = BUFFER_SIZE;
dma_buf = (char *)contigmalloc(dma_buflen, M_DEVBUF, M_NOWAIT,
0ul, 0xfffffful, 1ul, 0x10000ul);
if (!dma_buf) {
uprintf("satlink: Failed to allocate a DMA buffer\n");
return ENOMEM;
}
--
Christopher Masto Director of Operations S NetMonger Communications
chris@netmonger.net info@netmonger.net SSS http://www.netmonger.net
\_/
Microsoft's biggest and most dangerous contribution to the software
industry may be the degree to which it has lowered user expectations.
- ESTHER SCHINDLER, OS/2 Magazine
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