• Xilinx vs ...

    Antti Lukats09/01/2015 at 19:31 1 comment

    Xilinx is de-facto the FPGA company. The biggest and...

    For me Peter Alfke was Xilinx, the one who made Xilinx.

    He is no longer able to influence the development of Xilinx.

    I do not know if there would have been a difference, maybe.

    As of today Xilinx message is clear, this can be read from their website

    • do not use any of our CPLD in any of the new designs
    • do not use anything else than series 7 in any new designs

    The smalest FPGA Xilinx has today, is Artix A15T.

    You can fit an 32 bit SoftProcessor + MMU + DDR Controller IP Core + all peripherals that are needed to boot standard Linux into A15T.

    When I started with Xilinx FPGA's their FPGA had 64 Flip Flops. It was fascinating back then.

    It is REALLY fascinating now.

    Go take the path, go for 7.

  • Embedded Instruments

    Antti Lukats08/26/2015 at 20:20 3 comments

    As FPGAs can have many things working in parallel and may not contain an embedded processor at all then special tools are used for debugging. Most FPGA vendors have "embedded instruments" that can be added to your design and that provide visibility into the hardware.

    Xilinx - Chipscope, now Vivado Labtools (requires paid license)

    Altera - SignalTap (free)

    Lattice - Reveal (free)

    Microsemi - need to figure out

    There are some attempts for platform neutral or cross platform embeded instruments, Altium is/has tried this and opencores OpenRisc seems to have something too.

    Sump LA can of course also be used for internal debug..

  • VHDL vs Verilog

    Antti Lukats08/26/2015 at 20:07 2 comments

      Going random:

      1. it is of benefit to be able at least to understand both
      2. in many cases it is possible to use them mixed in same design
      3. verilog == c
      4. VHDL == Pascal (Module)
      5. if you use ICE FGAS, with verilog less hassle
      6. ASIC world prefers verilog
      7. FPGA world prefers VHDL
      8. simulation testbenches are easier in verilog

      There is no one winner.

  • FPGA use Example 2: glue logic replacement

    Antti Lukats08/23/2015 at 18:57 0 comments

      We can not always avoid the use of "glue logic" - this is fine, as long it is limited to few tiny logic gates or so.

      If we need more, then it would maybe already make sense to implement this "glue logic" in CPLD.

      Wait CPLD's do not exist any more. They have been replaced with small FPGA's now!

      Example, if we need:

      1. two tinylogic gates
      2. two signals converted from 1.8V logic to 3.3V logic

      We can of course use still glue logic and level shifters, but we may already consider using Lattice machXO2-256 in QFN32 package.

      So simple replacement of some small glue logic may get an FPGA into the game.

      The benefit? We do not need to source the different components (the logic ic, the level shifter IC), we just take the one part we have in stock, the FPGA and implement that logic.

  • FPGA use Example 1: MCU is immersed

    Antti Lukats08/23/2015 at 18:40 0 comments

      This is real world example of real product.

      Description

      1. relatively small custom logic handling some custom protocol
      2. some small slow management: SD Card initialization, reading a file..

      This could be done as: small CPLD as glue that helps with the "custom protocol" + some MCU - the classical solution.

      If we add the prices of CPLD + Flash MCU, we end up at say 3 USD at least.

      Small FPGA's are also in that price range - so in this example a small soft-core processor was fit into the FPGA along with the custom logic. The soft-core was very simple and had very small code memory, so it required a lot of optimization on the software side. But as it was targeting volume production this optimization did make sense.

      This was many years ago, there are new FPGA's families out now, and you can get more for the same price now.

      This is one example where "MCU was eliminated" and where it also made sense - the price, that FPGA did also cost about 3 USD and it replaced BOTH the CPLD and MCU together.

      Simple replacement of MCU in project where MCU can handle it all usually does not make sense.

  • FPGA: What are they?

    Antti Lukats08/23/2015 at 18:17 0 comments

    The definition has changed and is changed, the best description would be that they are "programmable hardware" based on architecture that is "scale-able" like an array. This scaling in 2 directions makes FPGA's different from classic CPLD's where prices of the silicon go up very quickly when the CPLD goes larger. This is the reason why classic CPLD's are vanishing - they are being replaced with small FPGA's that fill the gap. Altera MAX 2, V, 10, Lattice XO2, XO3 can be considered as CPLD, and they target some CPLD markets, but they are actually small FPGA's as of the architecture.

    Simple logic circuits are arranged in 2 dimensional array, with programmable interconnect. Very large FPGA's are 3D in that sense that those 2D arrays are layered with additional "vertical" interconnections.