Yet another modelsim problem

[Thomas]

Completed process "Generate Post-Translate Simulation Model".

ERROR: Hidden remap failed
Reason:

Launching Application for process "Simulate Post-Translate VHDL Model".



not only the software's stupid enough to launch the GUI after the error,
but there is not a single entry about this error in the xilinx database, on
the modelsim server or even in google (but me complaining about the same
problem a month ago)
The 'reason' field is as useful as usual this time they just didn't
bother typing a message that makes no sense, they just left it empty.

here's the code:

process(Reset, MasterClock) is
variable counter : std_logic_vector(2 downto 0);
begin
if(Reset = '1') then
counter := "000";
elsif(rising_edge(MasterClock)) then
dividedclock <= counter(2);
counter := counter + 1;
end if;
end process;

so, all the calls to modelsim, regardless of the type (post translate, post
map, etc) fail the same way.

then 'generated expected simulation results' yields another interesting
problem:

if, in the timing constraints, I select the clock to be rising edge only,
it works; if I pick dual edge, it just 'skips' cycles every 30 or so in the
display and everything gets out of sync...

Any ideas?

 

[K Mussatt]

The FPGAs I have worked and do work with do not allow for a dual edged CLK.
Assuming your does and /or assuming the
synthesizer does some neat trick to allow this for your FPGA, maybe you
could specifiy rising clock edge if in the layer above
this entity, you had a faster clock divide by 2 to make this clock that you
are using here. I dont' know if that is a possibility, but
I do remember running into some odd synthesis problems once trying to make a
dual edged clock.

Also, it has been my experience to 'not' do a divided clock by using one of
the bits, but rather to use it as an enable to drive
something maintaining sync with the one and only true clock.

PROCESS abc (CLK, RESET) BEGIN

DIV_2_EN <= COUNTER(2); -- pick the bit off you want to use
DIV_2_EN_R <= DIV_2_EN; -- make another signal delayed by one (true) clk
value
END PROCESS abc
--outside of the CLK do this:
DIV2CLK <= '1' when DIV_2_EN ='1' and DIV_2_EN_R = '0' else '0'; -- this is
not a 50% duty cycle clock, but it has the correct freq. of CLK/2

-Kip