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Parameters and pcells in ADE XL

kvntien

Hi all,

 I have a schematic pcell that generates an n-stage chain of (non-pcell) instances, each with different instance parameters.  To do this, I have a pcell string parameter 'numStages' (also defined in the CDF for the cell), and something in the pcDefinePCell let block like

n = atoi( numStages )
for( inst 1 n ....

I'd like to be able to sweep this parameter for optimisation in ADE by assigning it a design variable. First problem I ran into is, of course, when pcell evaluation happens, numStages is a text string representing a design variable, so atoi( numStages ) is nil. To get around that, I have

if( n == nil then n=round( VAR( numStages ) ) ) 

Not the most foolproof, but at least it seems to work in ADE L. When I try to move it to ADE XL for global optimisation, it fails: all instances of the pcell at every design point are instantiated as if numStages were set equal to the value it takes on in the first design point.

Is this due to the pcell evaluation only happening once, then ADE XL just changing the parameter declaration line in subsequent netlists? Either way, does anyone have any insight into how I can make this work? Or is this a fool's errand... 

Thanks,
Kevin 

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  • Andrew Beckett

    Hi Kevin,

    I also just tried the parameterization flow - and that doesn't work. The reason is that it's being smart to allow for something we've not turned on yet, which is running the parameter variations in the simulator memory without needing the simulator to restart (essentially similar to spectre's "interactive" mode).

    Anyway, the reason why I thought it might work is because when you alter a parameter using the Variables and Parameters assistant, it doesn't really change the design - it might be readonly, for example. So what happens is that in the ICRP background process it modifies the design in "scratch" mode (which is in memory only, and not saved) and then netlists the modified design. However, if you put a sweep on a parameter, it netlists it as a spectre parameter called DPAR_1., DPAR_2 etc - and hence it doesn't actually have to create a whole new netlist for each point in the sweep in practice - only the parameters line at the  top varies (this is faster, because it doesn't really need to re-netlist, just assemble the new netlist for that point in the sweep).

    So I think this is doomed to failure, sorry!

    Regards,

    Andrew.

Reply
  • Andrew Beckett

    Hi Kevin,

    I also just tried the parameterization flow - and that doesn't work. The reason is that it's being smart to allow for something we've not turned on yet, which is running the parameter variations in the simulator memory without needing the simulator to restart (essentially similar to spectre's "interactive" mode).

    Anyway, the reason why I thought it might work is because when you alter a parameter using the Variables and Parameters assistant, it doesn't really change the design - it might be readonly, for example. So what happens is that in the ICRP background process it modifies the design in "scratch" mode (which is in memory only, and not saved) and then netlists the modified design. However, if you put a sweep on a parameter, it netlists it as a spectre parameter called DPAR_1., DPAR_2 etc - and hence it doesn't actually have to create a whole new netlist for each point in the sweep in practice - only the parameters line at the  top varies (this is faster, because it doesn't really need to re-netlist, just assemble the new netlist for that point in the sweep).

    So I think this is doomed to failure, sorry!

    Regards,

    Andrew.

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