Date: Wed, 01 Dec 1999 21:26:43 -0800 From: Mike Smith <msmith@freebsd.org> To: Zhihui Zhang <zzhang@cs.binghamton.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: memory-to-memory copy Message-ID: <199912020526.VAA00818@mass.cdrom.com> In-Reply-To: Your message of "Wed, 01 Dec 1999 16:25:22 EST." <Pine.GSO.3.96.991201161752.5996A-100000@sol.cs.binghamton.edu>
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> > I used to know that memory to memory copy is done by the DMA controller in > the I/O bridge (Actually, this knowledge confues me because DMA controller > normally does not store the data that pass through it. Now the source and > destination are both memory, how can it achieve this at the same time with > one memory bus?). Almost nobody does memory-to-memory copy with DMA controllers. You certainly don't do it on the PC. > I was also told that the function bcopy() is used to > setup DMA. No, bcopy is used to move data from one place to another using the CPU. > Now I look at the bcopy() function in i386/support.s, I only > see instructions like "rep movsb". So how is the memory-to-memory copy > done in FreeBSD? With bcopy(). -- \\ Give a man a fish, and you feed him for a day. \\ Mike Smith \\ Tell him he should learn how to fish himself, \\ msmith@freebsd.org \\ and he'll hate you for a lifetime. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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