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Old 04-12-2005, 10:07 PM
Andrew Holme
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Default Quartus POWER_UP_LEVEL bug?

I want a FF in my EPM7128S project to be '0' at power-up; be later set by an
external input; and never subsequently reset. I placed an SRFF with S to
the external input; clock to the clock; and R to ground. I assumed it would
power-up at '0' but I got analysis and synthesis errors:

"Info: Power-up level of register inst is not specified -- using unspecified
power-up level"

and "output pins are stuck at VCC or GND" - so I created an assignment:

set_instance_assignment -name POWER_UP_LEVEL LOW -to inst

I was surprised it needed this, but it seems to work. That sorted, I placed
an inverter between the Q output of the SRFF and an external output pin - I
want the FF to drive an external active-low signal. This doesn't work in
the simulator or the real silicon: the output is permanently asserted. But,
if I connect another output directly to q - so I have both q and /q output
pins - then it works!

I'm guessing that Quartus can't invert the signal between the macrocell FF
and output pin, so it needs to use another macrocell just for the inverter,
but something goes wrong with the optimisation. Am I warm? Is this a known
bug? Is there some option I need to set, or must I dedicate an output pin
for the unwanted true q - just to make the /q output work??

I'm using Quartus II 4.1 Web Edition.

You can download a Quartus archive of this from
http://www.holmea.demon.co.uk/Misc/Test.qar
Try it first as-is, then delete the true output and re-run the simulation.

TIA




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Old 04-13-2005, 05:05 AM
Subroto Datta
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Default Re: Quartus POWER_UP_LEVEL bug?

Andrew can you send me your email so that an engineer can contact you
on this. Thanks for the test case and we are working on it.

Subroto Datta
Altera Corp.

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  #3 (permalink)  
Old 04-13-2005, 10:17 AM
Andrew Holme
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Default Re: Quartus POWER_UP_LEVEL bug?


Subroto Datta wrote:
> Andrew can you send me your email so that an engineer can contact you
> on this. Thanks for the test case and we are working on it.
>
> Subroto Datta
> Altera Corp.


Thanks.

My e-mail is here http://www.holmea.demon.co.uk/IMG/email.gif

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