Am Samstag 12 März 2011, 14:04:24 schrieben Sie: > On Mar 12, 2011, at 5:28 AM, Rolf Eike Beer wrote: > > David Hagood wrote: > >> On Fri, 2011-03-11 at 13:45 -0800, Greg KH wrote: > >>> What was the response? > >> > >> Mostly "This always comes up when people do FPGAs and they always do it > >> wrong." > >> And when I asked "OK, so what is right?" <crickets_chirp.wav> > >> > >> There's nothing like "here's how an FPGA might trigger a hot plug > >> event." or "here's how your driver can trigger a hot plug event" or > >> anything like that. > > > > First you need the device configurable do have it configured ;) That can > > either be that it already loads a design on bootup (e.g. from SPI) or you > > use a non-FPGA bridge chip (e.g. one of those crappy PLX9656 things). > > For the in- FPGA thing you need something that comes up fast enough for > > the initial scan time limit (IIRC ~50ms or something like that). > > We don't have such a bridge. We have one FPGA (virtex5 or spartan6) and > this is a pretty strong design requirement. > > > For Xilinx FPGAs they e.g. support "compressed bitstreams" so they can > > configure all identical blocks in parallel. If you leave the initial > > design mostly empty you can shrink the size of the bitstream and with it > > the configuration time to be small enough. For newer Xilinx chips (IIRC > > Spartan 6) there is even a solution directly from Xilinx doing exactly > > this. > > If I unserstand correctly, this would still imply a PROM next to the FPGA, > something I want to avoid. I would like to send the bitstream to the FPGA > directly from a filesystem file to SPI from a driver or userspace. Yes. But how do you plan to get that bitstream into the FPGA? If the device is not reachable by PCI you need to plug in an external cable or something. > > Coming up with a physically connected but PCI-wise dead board doesn't > > seem like a good idea to me as this basically gives you no benefit but > > makes accessing the device harder. > > Unless there is something else I don't see, I still think this is the way > to go for us. YMMV. I don't like it. Eike
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