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Greetings, How can I perform pass-through fitting (place and route)

Greetings,

 

I'm trying to implement the following design on a Cyclone II DE2:

20181015_234606[1].jpg

 

 

It is a cell of a special type of a PUF (physically unclonable function) called the TSRAM PUF, where it consists of cross-coupled pairs of tristate inverters. The inputs to the system are the enable signals, and the single output to the signal is the logic level that settles at the lower_response node (the upper_response node can also be taken as the output instead).

 

So I started out by designing a single tristate inverter like so:

Capture.PNG

 

 

And then I created a symbol out of the it, before using it to create the complete design:

Capture.PNG

 

 

 

There are many criteria that has to be satisfied in order for this design to work (I'll post the others as separate questions), one of them is that the circuit has to be physically symmetric, that is, the delay from each input/output of the tristate inverters to its facing node (lower or upper response) must be equal, and in order to do that, I have to be able to work with the individual tristate inverters in the chip planner, however, when I compile, the compiler "washes away" my design and leaves me with this:

Capture.PNG

 

 

My dilemma is that how can I force the compiler to "pass-through" my tristate inverters to the chip planner as they are without any optimization or change?

 

Any help or reference is highly appreciated.

 

If there is any additional information required, then please let me know.

 

Thank you all in advance,

My best regards.

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7 Replies
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Employee
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Re: Greetings, How can I perform pass-through fitting (place and route)

​Are you able to capture the technologies map viewer for tristate inverter block and overview of the design?

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Beginner
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Re: Greetings, How can I perform pass-through fitting (place and route)

Yes, below is the tech. map viewer for the tristate inverter:

Capture.PNG

And here is the one for the overall design:

Capture2.PNG

 

Additionally, here is the one for the tristate inverter instance (the green blocks above):

Capture3.PNG

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Employee
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Re: Greetings, How can I perform pass-through fitting (place and route)

In FPGA architecture, there is no tristate primitive component in the core, specifically in LE block. Look at Cyclone II LE structure https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/cyc2/cyc2_cii5v1.pdf, Figure 2-3 LE CII.JPGTristate only exists at the input or output port. So this is why your "tristate inverter" is translated to a mux. It is not possible to implement such design in FPGA.

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Beginner
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Re: Greetings, How can I perform pass-through fitting (place and route)

Is it possible to implement the design on any Altera FPGA other than the Cyclone II?

 

What about Xilinx FPGAs? Because I have a paper that implemented the same design on a Xilinx Virtex II (even though I didn't find any tristate support in its CLBs), a snippet of the paper is shown below:

20180921_161028[1].jpg

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Employee
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Re: Greetings, How can I perform pass-through fitting (place and route)

What I understand is all of Intel FPGAs do not have any tristate ​built either in ALM or LE primitive block. Checked on the Virtex II device datasheet, I believe it have it in their CLB.

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Beginner
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Re: Greetings, How can I perform pass-through fitting (place and route)

May I ask you to point out exactly where you found the tristate component in the Xilinx datasheet:

Capture.PNG

 

Your help is highly appreciated.

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Employee
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Re: Greetings, How can I perform pass-through fitting (place and route)

Please look at section of 3 state buffers​

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