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List:       freebsd-hackers
Subject:    Re: ISA limmitation of 16MB for DMA [wschlanger@usa.net: ]
From:       Mike Smith <mike () smith ! net ! au>
Date:       1999-01-31 14:52:25
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FreeBSD uses the time-honoured technique of "bounce buffering" - it
maintains a pool of buffers in ISA-addressable space, and allocates them
as required to back pending ISA busmaster transactions.

This is handled transparently by the bus-space DMA code, which adds 
several levels of indirection to the issue.  You may find the older 
kernels (2.2.x) technique which involved explicit cooperation by the 
driver easier to understand.

> ----- Forwarded message from Willow Schlanger <wschlanger@usa.net> -----
> 
> Thanks. Would you happen to know where I can learn how FreeBSD gets
> around the ISA limmitation of 16MB for DMA? Is there a source file I can
> see that demonstrates this?
> 
> Thanks in advance,
> Willow Schlanger
> 
> Wolfram Schneider wrote:
> > 
> > On 1999-01-24 03:49:02 -0800, Willow Schlanger wrote:
> > > Q: Hi. I'm a programmer and I'm interested in the kernel source code for
> > > FreeBSD. I can't seem to find it anywhere - I've tried different FTPs
> > > FreeBSD.org mentions, but I can never figure them out. I use DOS and
> > > Windows 95/98 -- do I need some special program to get the assembly
> > > language and C/++ sources?
> > 
> > [cc: freebsd-questions]
> > 
> > The FreeBSD kernel sources code is available at
> > 
> > ftp://ftp.freebsd.org/pub/FreeBSD/FreeBSD-current/src/sys
> > 
> > or
> > http://www.freebsd.org/cgi/cvsweb.cgi/src/sys
> > 
> > >
> > > Can you help me?
> > >
> > > Thanks in advance,
> > > Willow Schlanger
> > 
> > --
> > Wolfram Schneider <wosch@freebsd.org> http://freebsd.org/~w/
> 
> ----- End forwarded message -----
> 
> -- 
> Wolfram Schneider <wosch@freebsd.org> http://freebsd.org/~w/
> 
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-- 
\\  Sometimes you're ahead,       \\  Mike Smith
\\  sometimes you're behind.      \\  mike@smith.net.au
\\  The race is long, and in the  \\  msmith@freebsd.org
\\  end it's only with yourself.  \\  msmith@cdrom.com



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