Date: Tue, 14 Oct 2008 20:39:39 +0100 From: Pegasus Mc Cleaft <ken@mthelicon.com> To: freebsd-hackers@freebsd.org Subject: Re: [Doubt] Can a PCI device communicate with another PCI or other device? Message-ID: <200810142039.39287.ken@mthelicon.com> In-Reply-To: <e6a0706a0810141132n1a1d1a9cn4a50ffc727640e13@mail.gmail.com> References: <e6a0706a0810141132n1a1d1a9cn4a50ffc727640e13@mail.gmail.com>
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On Tuesday 14 October 2008 19:32:47 Srinivas wrote: > Hello, > > I have a small doubt. > > Suppose I have a PCI card with a general purpose CPU on it. Could it be > able to communicate with another PCI device or ISA device(lets say IDE ha= rd > disk)? Hi Srinivas,=20 Others may have a different opinion on this, and I am curious to see there= =20 input to this question as well. I tried doing something like this years ago= =20 with the Blackfin processor, but I found it to be not a good idea. While I= =20 could DMA transfer memory from the DSP into the physical memory of another= =20 device (In my case, the HD controller) I couldn't take control of IRQ=B4s. = Other=20 potential problems arose that turned me off to the whole idea (Data=20 concurrency between the DSP->HD and the host->HD). Even if you got past the= se=20 problems you would still face having to deal with any number of filing syst= ems=20 formats.=20 I found it much easier to make a device driver and service/daemon on the h= ost=20 machine that proxi-requested things for the DSP board and burped it into ra= m=20 that the DSP could then grab and process (or dump to disk from, in the othe= r=20 direction). While the speed may not be brilliant, it made things a lot easi= er=20 for me to manage on a software level.=20 In later revisions, I re-spun the PCB so it had an IDE controller local to= =20 the DSP and stuck an PLX-Tech PCI to PCI bridge between the host and the DS= P=20 so I could manage 2 small memory windows between the two (One for API=20 commands, and the other data) with a single IRQ back to the host. This allo= wed=20 me to have a high-speed IDE port local to the DSP where it was needed, and = a=20 slower link back to the host CPU for pulling video files, etc.=20 Hope this helps, Peg
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