nexys video memories

[sosso]

hi everyone, 

        in the Nexys Video, there is two external memories, please correct me if I'm wrong  :

          --The QSPi,is the memories which stores the configuration ( FPGA bitsream is the way to configure to create the block design) of the FPGA to make our block design.

          -- The DDR3 is used as a memory which stores what the results of what is going on. works as a RAM in a PC

          -- the cache memory, which is created after inserting the bitstream stores the instructions and data of the program.

[D@n]

@sosso,

You are essentially correct.  I think there are three additional flash memories on the board, but they are small and not nearly as easy to use.  The cache you mention above, though, isn't an "external" memory--that's all within the FPGA.

Dan

[sosso]

D@n,

       Yes, so my problem is what is the role of the DDR ram?

                    thanks you 

[D@n]

@sosso,

While the flash can be written, writing to it tends to be very slow.  As a result, it works better as a ROM than a RAM.  Further, the flash is still much slower than the DDR3 SDRAM.  The DDR3 SDRAM is a large, full size, RAM for ... whatever purpose you would like to use a *large* RAM for.  It's slower than the block RAM within the FPGA, but it's also much larger than any block RAM within the FPGA.  On my Nexys Video, I'm intending to use the RAM to support a video frame buffer.

Dan