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vhdl code generators ( crossposted in comp.hardware.fpga)

 
 
abe
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      11-19-2008
does anybody have a clear opinion about code generators ( c-> vhdl ,
matlab-> vhdl, etc..) that are around? Are they really irreplaceable
in complex applications (i.e DSP) as the vendors say?
 
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Tricky
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      11-19-2008
On 19 Nov, 15:47, abe <(E-Mail Removed)> wrote:
> does anybody have a clear opinion about code generators ( c-> vhdl ,
> matlab-> vhdl, etc..) that are around? Are they really irreplaceable
> in complex applications (i.e DSP) as the vendors say?


We recently had a talk from the guys at mathworks about Simulink.

From what I can tell, and from the opinion of the software and
hardware guys, is that the Software code generation is fairly mature
and pretty good.
We have done a simple project with VHDL code generation, and it does
work, but I wouldnt really call it readable, or maintainable in code
form, but the idea is all your source is the Simulink system diagrams.

Here is an example of the code generated for a multiplier:

signal input_a : unsigned(7 downto 0);
signal input_b : unsigned(7 downto 0);
signal mult_res : usngiend(15 downto 0);
signal mult_res_resize : unsigned(7 downto );
signal mult_res_register : unsigned(7 downto 0);
...
mult_res <= input_a * input_b;
mult_res_resize <= mult_res(15 downto ;

process(clk)
begin
if rising_edge(clk) then
mult_res_register <= mult_res_resize;
end if;
end process;

Now when you add that in with resize functions all over the page, it
quickly becomes unreadable. We had a simple system with about 4 fixed
point multipliers, and about 6 adders, and I wouldnt want to try and
re-organise it for efficiancy. If it was more complex, I wouldnt even
want to look at the output VHDL.

It is not meant to replace hand written code, it is meant to be a
system level specifcation that has the tools to generate code that can
be used to put onto an FPGA. It appears to be very useful at allowing
the user to specify what is software and what is hardware. I got the
feeling that for more complex systems, hand written VHDL would still
be far more maintainable and efficient for now. But it should work.

One point to note: you will need digital electronic knowledge to
ensure you create the hardware versions of the top level functions
properly.
 
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