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i need to produce a signal with rising edge alone of 1 micro second in test bench, please help.
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> i need to produce a signal with rising edge alone of 1 micro second in > test bench, please help. Several parameters are missing. What is the lower value (bottom horizontal line) and what is the upper value (top horizontal line). They cannot be simply '0' and '1', because in digital levels (like the "bit" type or the "std_logic" type) there is nothing in between... Why do you write HOW you want to solve something, and not simply, WHAT you need this for?
> rising edge
Maybe you are wrong in VHDL/Verilog forum? If you wand to do analog
simulation, you should address to (P)Spice or similar forum?
It is of course (without any problems) possible to generate "analog" values in VHDL. This here generates a real ramp from 0.0 to 1.0 between 10 and 11 us:
library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.math_real.ALL; entity ramp is Port (o : out real); end ramp; architecture Behavioral of ramp is begin process begin wait for 10 ns; if now<10 us then -- before the "rising edge" o <= 0.0; elsif now>11 us then -- after the "rising edge" o <= 1.0; else -- Ladies and Gentelemen: the "rising edge" o <= real((now-10 us)/1 ns)/1000.0; end if; end process; end Behavioral; |
>It is of course (without any problems) possible to generate "analog" >values in VHDL. Cool, now you just have to find an input where you can feed it to. ;-) @sathya sree Unless you are a little more specific about your intentions what you want to do in which context, you won't get useful advice. :-(
Peter K. wrote: > Cool, now you just have to find an input where you can feed it to. ;-) Because all of this discussion is in my eyes only good for simulation, you can feed it everywhere... ;-) But of course something like this may be of interest also in generating stimuli in a testbench for a synthesizable device. Of course the real value you get up there must then be converted to any kind of digital vector. But that indeed wil involve only one additional line of code.
thanku friends for ur kind response am new in the field of vhdl, now am working on rtx1280rh fpga the processor vl generate a watch dog clear pulse, in the absence of this pulse fpga vl generate a nonmaskable interupt. in vhdl programming in testbench stimulus i found all signal transition from 0 to 1 0r 1 to 0. the nmi is generated at the falling edge of a data ready signal. the error found was continous unpredictable occurrence of nmi,i believe dat if i could jst make a change in the falling edge of data ready, rather dan a sudden transition from 1 to 0 in test bench ,the problem could be solved
> rtx1280rh fpga Google does find absolutely nothing about that... > the processor vl generate a watch dog clear pulse, in the absence of > this pulse fpga vl generate a nonmaskable interupt. This sounds like a pure digital design. > i believe dat if i could jst make a change in the falling edge of data > ready, rather dan a sudden transition from 1 to 0 in test bench ,the > problem could be solved Why do you believe that? You have a pure digital design, why do you want to trick around with analog values? If there is any problem it will be a timing or a behaviour problem. But nothing you can solve with "a little magic". > the error found was continous unpredictable occurrence of nmi, How did you find that error? With a test bench? Or in "real life"? > i believe Maybe thats the wrong way...
its rtx 2010 processor and fpga rh1280 ofcourse its a pure digital design , is dr any way i can attain such a signal in vhdl??????
entity testbench is
end testbench;
architecture behavioral of testbench is
signal tb_Aclr:std_logic;
signal tb_WDclr:std_logic;
signal tb_Xdrdy:std_logic;
signal tb_Shiftout_NMI:std_logic;
signal tb_Shiftout_PReset:std_logic;
signal tb_Clock6MHz:std_logic :='0');
component WDModule_behave is
port(Aclr:in std_logic;
WDclr:in std_logic;
Xdrdy:in std_logic;
Shiftout_NMI:out std_logic;
Shiftout_PReset:out std_logic;
Clock6MHz:in std_logic);
end component;
ramp:process
variable o:out real;
begin
wait for 495 us;
if now<495 us then -- before the "rising edge"
o <= 0.0;
elsif now>496 us then -- after the "rising edge"
o <= 1.0;
else -- the "rising edge"
o <= real((now-495 us)/1 ns)/1000.0;
end if;
end process;
tb_Xdrdy<=o;
constant tb_Clk:time:=166ns;
begin
tb_WDclr <='0','1' after 557us,'0' after 557.555us,'1' after 667us,'0'
after 667.555us;
tb_Clock6MHz <=not tb_Clock6MHz after tb_Clk/2.0;
tb_Aclr ='0','1' after 480500ns,'0' after 480550ns,'1' after
482500ns,'0' after 482800ns,'1' after 1556us,'0' after 1556.3us
WDModule_behave_0:WDModule_behave port map
(tb_Aclr,tb_WDclr,tb_Xdrdy:std_logic,tb_Shiftout_NMI,tb_Shiftout_PReset,
tb_Clock6MHz);
end Behavioral;
--i want to control xdrdy rising edge, can any one point out the error
in this programming???????
> --i want to control xdrdy rising edge, can any one point out the error > in this programming??????? > Xdrdy:in std_logic; A std_logic has 9 possible values, starting with U then X, 0, 1, Z, W, L, H to - (thats the way, the type std_logic is defined!) And there is absolutely no way to assign a value half between 0 and 1 to a std_logic. So the main problem is, that you obviously do not have the faintest idea what you are doing! Answer this question in a conclusive way: WHY do you think, your problem could be solved with "a slow rising edge"?
"a slow rising edge"????? no i need a fast rising edge the xdrdy coming is not an ideal(lyk a perfect square wave)one, it is having rising and falling edge, i need 2 control it and make them perfect square like,becoz of this falling edge nmi is generated
> the xdrdy coming is not an ideal You cannot simulate a "not ideal" std_logic input! So the problem does not come from and is not solvable within simulation. > the xdrdy coming is not an ideal(lyk a perfect square wave)one So that is a signal in real life, not just in simulation? You can measure that signal with an oscilloscope? How does it look like? What you need to "sharpen" a slow rising signal in real life is a schmitttrigger, or a debouncing unit with edge detection. But again: you cannot simulate that "slow" slope with a std_logic type!
ofcourse it was viewd in oscilloscope , then only it was analysed dat its bcoz of that slow falling edge error is occuring,practically its nt possible to attain ideal one, bt atleast we can reduce the falling edge?????
> ofcourse it was viewd in oscilloscope >> ... >>> a sudden transition from 1 to 0 in test bench Youre mixing and muddling up real life and simulation. And that makes it a hard task to help you. For future: it is a BIG difference betwenn simulation and real life. Although a design may run perfectly in simulation, it may do not a single step in real life. And so it is ESSENTIALLY to get clear, where the problem is! > we can reduce the falling edge??? You CANNOT reduce the slope. It is defined by hardware. Find out, WHY thata signals slope isn't steep enough. See, how you can fix it at the source of that signal. If a fix there is not possible then YOUR design must cope up with a slow falling slope. And here are two ways: 1. Take an additional schmitttrigger buffer outside the FPGA (fast, but with impact on hardware) or 2. Use "debouncing and edge detection" inside the FPGA (will produce several cycles latency)
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