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From VHDL to gates and LUTs (newbie)

 
 
SanSaurus
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      08-10-2004
Hello NG!

I'm learning VHDL, but still have to understand how my VHDL-code will
end up as gates and LUTs etc in a FPGA...

I did search google, but all I found was some complex sites describing
how it worked, so I try this NG. Good links which describes the above
for a newbie are highly appreciated! )

1) Default-values?
I have a signal in my architecture of a entity, which I give a default
value, like this:
signal counter : std_logic_vector(7 downto 0) := (others => '0');

Will this default value be put in the FPGA as well? Or should I code
my architecture as if it could be undefined as default?
Maybe it differ from FPGA to FPGA? I'm using a FPGA from the Spartan
family.

2) What's happening when I synthesize?
Can someone in simple steps describe what is happening when I
synthesize, implement design, generate programming file etc. from my
VHDL-code? That could be cool! (I'm using a free version of Xilinx
ISE, but I guess the terms are general).

3) UCF-files
User Constraints Files are mainly (at least for a beginner like me)
how my pins of my FPGA are connected to the outer world, right? - and
how I attach them to inputs on my entities in my VHDL-code.

4) How is my FPGA "booted"?
Now everything has been put in the FPGA and I power up FPGA. Will it
automatically start with the default values right away? Should I wait
for some time, before my entities starts working as expected? I guess
it takes some times to initialize the FPGA? I guess you will refer me
to the datasheets of the specific FPGA on this... ;o) I want to know
if there are some common things, that you have to consider about this
issue. )

--
SanSaurus

 
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Mike Treseler
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      08-11-2004
SanSaurus wrote:

> Default-values?
> I have a signal in my architecture of a entity, which I give a default
> value, like this:
> signal counter : std_logic_vector(7 downto 0) := (others => '0');
>
> Will this default value be put in the FPGA as well?


Usually not.

Use a reset input and code specific reset assigments.

> What's happening when I synthesize?


A netlist is generated that simulates the
same as your code.

> How is my FPGA "booted"?
> Now everything has been put in the FPGA and I power up FPGA.


All pins will be 'Z' until the image file is loaded.
Next the reset pulse is applied, and outputs will
start working the same as the functional simulation.

-- Mike Treseler
 
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Jeroen
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      08-12-2004

"SanSaurus" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hello NG!
>
> I'm learning VHDL, but still have to understand how my VHDL-code will
> end up as gates and LUTs etc in a FPGA...
>


Some synthesizers can provide a schematic view (gates, flipflops, muxs etc)
of what they have produced.

Jeroen


 
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