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From: Dave on 17 Apr 2008 12:43 Does anybody out there have a good methodology for determining your optimal FPGA pinouts, for making PCB layouts nice, pretty, and clean? The brute force method is fairly maddening. I'd be curious to hear if anybody has any 'tricks of the trade' here. Also, just out of curiosity, how many of you do your own PCB layout, versus farming it out? It would certainly save us a lot of money to buy the tools and do it ourselves, but it seems like laying out a board out well requires quite a bit of experience, especially a 6-8 layer board with high pin count FPGA's. We're just setting up a hardware shop here, and although I've been doing FPGA and board schematics design for a while, it's always been at a larger company with resources to farm the layout out, and we never did anything high-speed to really worry about the board layout too much. Thanks in advance for your opinions. Dave
From: Mike Treseler on 17 Apr 2008 13:33 Dave wrote: > Does anybody out there have a good methodology for determining your > optimal FPGA pinouts, for making PCB layouts nice, pretty, and clean? > The brute force method is fairly maddening. I'd be curious to hear if > anybody has any 'tricks of the trade' here. The best way to get good pinouts is to finish a working prototype of the hdl code before making the board. I let place and route make the first cut unconstrained and then clean up from there. > Also, just out of curiosity, how many of you do your own PCB layout, Not me. Whoever does this, should do it all day long, every day. > It would certainly save us a lot of money to > buy the tools and do it ourselves, The first pass might save some money, but by the time you have a working board you will be in the hole. > but it seems like laying out a > board out well requires quite a bit of experience, especially a 6-8 > layer board with high pin count FPGA's. That is correct. -- Mike Treseler
From: qrk on 17 Apr 2008 13:40 On Thu, 17 Apr 2008 09:43:09 -0700 (PDT), Dave <dhschetz(a)gmail.com> wrote: >Does anybody out there have a good methodology for determining your >optimal FPGA pinouts, for making PCB layouts nice, pretty, and clean? >The brute force method is fairly maddening. I'd be curious to hear if >anybody has any 'tricks of the trade' here. > >Also, just out of curiosity, how many of you do your own PCB layout, >versus farming it out? It would certainly save us a lot of money to >buy the tools and do it ourselves, but it seems like laying out a >board out well requires quite a bit of experience, especially a 6-8 >layer board with high pin count FPGA's. > >We're just setting up a hardware shop here, and although I've been >doing FPGA and board schematics design for a while, it's always been >at a larger company with resources to farm the layout out, and we >never did anything high-speed to really worry about the board layout >too much. Thanks in advance for your opinions. > >Dave Sure wish there was a slick way of doing FPGA pinouts. I usually use graph paper and figure out the FPGA pinout to other parts to minimize routing snarls. I do pcb layouts on my own and other folks designs. Our boards have high-speed routing, switching power supplies, and high-gain analog stuff; sometimes all on the same board. Unless the service bureau has someone who understands how to lay out such circuitry and place sensitive analog stuff near digital junk, it is more trouble to farm out than do it yourself if you want the board to work on the first cut. Doing your own layout will take a lot of learning to master the PCB layout program and what your board vendor can handle. It will take 5 to 10 complicated boards to become mildly proficient at layout. I don't know about saving cost. Your time may be better spent doing other activities rather than learning about layout and doing the layouts. The upside to doing your own layout - you control the whole design from start to finish. If you have a challenging layout, you'll have a much higher probability of having a working board on the first try which has hidden savings (getting to market earlier <- less troubleshooting + less respins). --- Mark
From: Joerg on 17 Apr 2008 13:50 qrk wrote: > On Thu, 17 Apr 2008 09:43:09 -0700 (PDT), Dave <dhschetz(a)gmail.com> > wrote: > >> Does anybody out there have a good methodology for determining your >> optimal FPGA pinouts, for making PCB layouts nice, pretty, and clean? >> The brute force method is fairly maddening. I'd be curious to hear if >> anybody has any 'tricks of the trade' here. >> >> Also, just out of curiosity, how many of you do your own PCB layout, >> versus farming it out? It would certainly save us a lot of money to >> buy the tools and do it ourselves, but it seems like laying out a >> board out well requires quite a bit of experience, especially a 6-8 >> layer board with high pin count FPGA's. >> >> We're just setting up a hardware shop here, and although I've been >> doing FPGA and board schematics design for a while, it's always been >> at a larger company with resources to farm the layout out, and we >> never did anything high-speed to really worry about the board layout >> too much. Thanks in advance for your opinions. >> >> Dave > > Sure wish there was a slick way of doing FPGA pinouts. I usually use > graph paper and figure out the FPGA pinout to other parts to minimize > routing snarls. > > I do pcb layouts on my own and other folks designs. Our boards have > high-speed routing, switching power supplies, and high-gain analog > stuff; sometimes all on the same board. Unless the service bureau has > someone who understands how to lay out such circuitry and place > sensitive analog stuff near digital junk, it is more trouble to farm > out than do it yourself if you want the board to work on the first > cut. > Or find a good layouter and develop a long-term business relationship. My layouter knows just from looking at a schematic which areas are critical. He's a lot older than I am and that is probably one of the reasons why his stuff works without much assistance from me. Nothing can replace a few decades of experience. > Doing your own layout will take a lot of learning to master the PCB > layout program and what your board vendor can handle. It will take 5 > to 10 complicated boards to become mildly proficient at layout. I > don't know about saving cost. Your time may be better spent doing > other activities rather than learning about layout and doing the > layouts. ... Yep, that's why I usually do not do my own layouts. Occassionally I route a small portion of a circuit and send that to my layouter. No DRC or anything, just to show him how I'd like it done. > ... The upside to doing your own layout - you control the whole > design from start to finish. If you have a challenging layout, you'll > have a much higher probability of having a working board on the first > try which has hidden savings (getting to market earlier <- less > troubleshooting + less respins). > > --- > Mark -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Symon on 17 Apr 2008 14:04
Dave wrote: > Does anybody out there have a good methodology for determining your > optimal FPGA pinouts, for making PCB layouts nice, pretty, and clean? > The brute force method is fairly maddening. I'd be curious to hear if > anybody has any 'tricks of the trade' here. > > Also, just out of curiosity, how many of you do your own PCB layout, > versus farming it out? It would certainly save us a lot of money to > buy the tools and do it ourselves, but it seems like laying out a > board out well requires quite a bit of experience, especially a 6-8 > layer board with high pin count FPGA's. > > We're just setting up a hardware shop here, and although I've been > doing FPGA and board schematics design for a while, it's always been > at a larger company with resources to farm the layout out, and we > never did anything high-speed to really worry about the board layout > too much. Thanks in advance for your opinions. > > Dave Hi Dave, I layout my own PCBs. Unlike Mike T., I don't let the FPGA tools pick the pinout. That said, it is important to consider carefully consider nets which might have tight timing, e.g. clocks. I reason that there is a lot more flexibility in the FPGA routing than on my PCB, and it's cheaper, so I can save most time and money by being flexible in the pinout. I set the banks the nets are to go on, and firm up the detailed pinout by swapping pins on the FPGAs banks during the PCB layout process. You need some experience in what your HDL code is gonna look like to be able to do this, but there you go. If you are adept at FPGA work, you'll find learning a PCB layout tool is a piece of cake. I also use laser drilled microvias from layer 1 to 2, which make the layout of big BGAs easier and saves layers. SI is easier also. The price is usually less this way; the layers outweigh the via expense. You don't need buried vias, IME. Some of my FPGA buddies and I have had bad experiences with contract PCB people. Sometimes they are knowledgeable and talented, but sometimes they are dogmatic idiots, and sometimes they are useless. If you go the contract route, it's important to closely monitor what they get up to so you find out early doors which type they are. Like you and Mike say, it depends a lot on your experience. If you've worked closely with your layout guys in the past, that'll be a big help to you. For sure, there's more than one way to skin a cat, but I enjoy PCB layout. YMMV, good luck with it. Cheers, Syms. p.s. One benefit to laying out the PCB yourself is that it can help you spot stupid mistakes in the circuit as you go. It forces you to look very closely at the layout. |