Newbie - VHDL Storage

[Carlos]

Hi,

As your guess from my question I'm quite new to VHDL.

I have an XILINX SPARTAN IIE FPGA (XC2S300E). For testing purposes I need
to store about 20,000,000 single bit values. In other words I'm sampling an
input at 4MHz for 5 seconds, and I want to store the value of the input
inside the FPGA. Apparently the FPGA has many MegaBytes of internal memory
so I would imagine the FPGA is capable of doing this.

I was hoping that I could just create a large signal like this:

signal store : bit_vector(20000000 downto 0);

And then just store the value of the input in the signal.

The problem is the synthesis seems to never finish.

Does anyone have any suggestions on how I can store all the values inside
the FPGA? Am I asking to much of the FPGA?

Thanks for any help,

 

[valentin tihomirov]

This question is more suitable in fpga newsgroup. The reason is that your
VHDL synthax is correct but Spartan may not have so many FF registers. It
may embody a general purpose memory though. Each cell of typical FPGA has
only one configurable FF register in addition to configurable and
service(that performs configuration) logic. This makes FPGA cell a very
expensive resource. Therefore, a dedicated storage device is much more
robust to keep high volume infrequently issued data. Check out SpartanII
specs and examples to know how make use of it.

 

[David R Brooks]

Think of what hardware you are describing. Here, a 20,000,000 way
decoder to select the bits (even if Spartan can hold them).
VHDL specifies that an impementation must support at least 256-wide
buses, but doesn't set a maximum. It won't be that big, however.

As another poster has said, use the Block RAMs. Even there, I doubt
you'll get 20,000,000 bits. The way to do it is to use a stock RAM
chip (dynamic?), and control that with your FPGA.

"Carlos" <Carlos@no_spam.com> wrote:

:Hi,
:
:As your guess from my question I'm quite new to VHDL.
:
:I have an XILINX SPARTAN IIE FPGA (XC2S300E). For testing purposes I need
:to store about 20,000,000 single bit values. In other words I'm sampling an
:input at 4MHz for 5 seconds, and I want to store the value of the input
:inside the FPGA. Apparently the FPGA has many MegaBytes of internal memory
:so I would imagine the FPGA is capable of doing this.
:
:I was hoping that I could just create a large signal like this:
:
:signal store : bit_vector(20000000 downto 0);
:
:And then just store the value of the input in the signal.
:
:The problem is the synthesis seems to never finish.
:
oes anyone have any suggestions on how I can store all the values inside
:the FPGA? Am I asking to much of the FPGA?
:
:Thanks for any help,
:
:
: