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Programming FPGAs with FLASH

Discussion in 'Electronic Design' started by Toni Merwec, Oct 29, 2007.

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  1. Toni Merwec

    Toni Merwec Guest

    Hi there,

    currently I am designing an FPGA board, featuring two Xilinx Virtex-4 FPGAs.
    It should be possible to program them with onboard Xilinx Platform FLASH
    PROMs as well as via JTAG with the IMPACT software. For ease of use and
    debugging all components should be part of one coherent JTAG chain.

    Now I'd like to know HOW to connect two FPGAs and two Platform FLASH devices
    in one JTAG chain so that each FPGA can be programmed through the associated
    FLASH? How is the identification done (i.e. which FLASH is associated with
    which FPGA?!)?

    Thanks alot in advance...

    Regards

    Toni
     
  2. tlbs101

    tlbs101 Guest

    Hi.

    I've done this several times in the past.

    Tie all the TCK and TMS signals in parallel.
    Tie each TDI to the next TDO. In your case it would be wise to tie
    the TDO signal from the Flash to the TDI of its FPGA, then tie the TDO
    signal of that FPGA to the TDI signal of the next Flash, etc. The
    JTAG connector will have the first flash TDI on a pin and the 2nd FPGA
    TDO as a pin.

    Impact will recognize the chain and show icons for each device. You
    select the flash you want to download your config file to, and Impact
    will write to that memory, only.

    Make sure you have the proper version of Impact and the proper version
    of the JTAG programming cable. Impact is very picky about cables and
    software versions.


    Hope this helps,
    Tom P.
     
  3. Nico Coesel

    Nico Coesel Guest

    The FPGA's serial configuration busses should be connected in series
    if you use one FLASH device. You let Impact create a bitstream with 2
    FPGA designs. Load this bitstream into the flash rom and you're ready
    to load the FPGA's. If you want to use 2 flash devices, connect the
    TDO and TDI from the flash devices in series. Impact will see the 2
    devices in series and you can assign a file to each of them.

    BTW, if you have some sort of microcontroller on your board, it might
    be easier / more convenient / cheaper to load the FPGAs from flash
    connected to the microcontroller.
     
  4. The devices should be displayed by their physical location in the
    chain. So you daisy chain the TDI/TDO pins in the physical position
    you want them to be displayed on screen. That's all you can really do
    if you have more than one of the same device on the chain.

    Dave.
     
  5. Toni Merwec

    Toni Merwec Guest

    Okay, thank you very much. I've done it that way now. But one more question:
    What about the DO pins from the PROMs to the FPGA. In the Platform Flash
    In-System Programmable Configuration PROMs data sheet ds123.pdf (page 18) it
    is recommended to tie the DO outputs of both PROMs together and connect the
    FPGAs in series. I don't see any reason to do it this way. What I would have
    done normally (without having read the user guide) is having the DO of one
    PROM connected to one FPGA (DIN) and the other DO of the second PROM to the
    the other DIN of the remaining FPGA. What is the reason not to do so, i.e.
    is there any reason? Any help is highly appreciated!

    Regards

    Toni
     
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