On Sun, 4 Jan 2009, Jon Elson wrote: > Date: Sun, 04 Jan 2009 11:57:53 -0600 > From: Jon Elson <el...@pico-systems.com> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> > Subject: Re: [Emc-users] OT: PDP11 > > Gene Heskett wrote: >> On Sunday 04 January 2009, Peter C. Wallace wrote: >> >> >>> On the other hand you can do a lot with a embedded 32 bit processor in a >>> FPGA (the ZPU for example uses about 20% of a 400K SP3, runs at ~ 100 MHz, >>> is BSD licensed and has a GCC toolchain) >>> >> >> Which again, sounds like a plus till you said 100mhz. That might do for >> servo >> driven machines but I'd guess it won't run steppers at usable speeds will it? >> >> > Well, if you are embedding in an FPGA, then it costs NOTHING to add in a > hardware step rate generator! > That's the whole BEAUTY of putting it all in an FPGA, if there's an > important function the CPU can't satisfy, add additional hardware to do it. > > But, EMC is very tied to doing everything in floating point, and the > FPGA CPU IP's generally don't have this. Most FPGAs that are not > designed from the ground up for DSP don't have the dedicated multiplier > logic to do well at this, either. If you want to do things with FPGAs, > it turns out that the smaller devices are QUITE reasonable in cost, but > the larger ones become very expensive. There are some really incredible > Xilinx chips out there in their Virtex series, but they cost $7800! Can > you imagine a single CHIP for that price? (Now, I'm not saying you need > one of these to put a CPU in, but you could easily be talking about a > $200+ chip for this. A $20 Arm9 starts looking a lot more affordable then.)
We've looked at the Virtex 5 series for PCIe FPGA cards but its still cheaper to use an external bridge... Actually a Spartan 3 400K part (~$14 for 144 pin) contains 16 18x18->36 hardware multipliers and you can easily fit multiple 32 bit CPUs inside with space left for (simple) peripherals. Spartan 3A FPGAs (also cheap) contain multiple fancier DSP blocks (DSP48) In all the current EMC configurations, the multipliers are unused, but we do use them in Our SoftDMC motion controller, and the next version of this firmware with a simple 32 bit processor uses the multipliers to support 1 clock multiply instructions (Our current 32 bit processor uses ~330 slices, (~10% of A 400k sp3) > > Jon > > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
