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# Claim in attached paper not understood

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#### ASIC_int

1) Y= '0'.

2) The netlist should not be a 2:1 mux. It is because casex is synthesizable. So it will try to produce a gate level structute where even if in='X' , the output should be 1'b0. Si the tool will try to look for gate in the library that can realize such a gate level netlist. So Y= '0' when in= x.

lostinxlation
lostinxlation

You still did not reply the following:
"A casex treats X as don't cares if they are in either the case expression or the case item".

What does it mean to state that casex treats case expression as don't care?

#### permute

casex is usually used because the cases can have "wildcards" in them, don't cares. Things that match a 0 or a 1. things like 8'b0001????. The issue with casex is that the input that is compared against this 8'b0001???? also treats x's in the same way.

thus an input of 8'bxxxxxxxx will match the 8'b0001???? case. it will also match every case in the case statement. as such, it will evaluate to the first case in the structure. This prevents x's from being propogated in the simulation -- the default case, or any other error-handling cases will never be reached.

#### lostinxlation

2) The netlist should not be a 2:1 mux. It is because casex is synthesizable. So it will try to produce a gate level structute where even if in='X' , the output should be 1'b0. Si the tool will try to look for gate in the library that can realize such a gate level netlist. So Y= '0' when in= x.
If you think the one and the only input that a netlist has gettting value X can get the output other than X, you are lacking a common sense in digital design. I bet you have never seen a transistor level circuit of a cell that must be learned before anything. What kind of gate can produce 0 or 1 when it gets X in one and the only input ?

Forget about Verilog and learn the basics.

You still did not reply the following:
"A casex treats X as don't cares if they are in either the case expression or the case item".

What does it mean to state that casex treats case expression as don't care?

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#### ASIC_int

If you think the one and the only input that a netlist has gettting value X can get the output other than X, you are lacking a common sense in digital design. I bet you have never seen a transistor level circuit of a cell that must be learned before anything. What kind of gate can produce 0 or 1 when it gets X in one and the only input ?

Forget about Verilog and learn the basics.

You are wrong here. I did not wrote or imply what you claimed. I wrote the tool will synthesize taking storage elements and combinational block such a circuit that will able to produce '0' or '1' with 'x' as input. However it may be difficult for you to realize such a circuit but I can visualize that.

Does the synthesis tool take care of the properties of casex like even if the case items are unknown it will be able to produce the valid outputs against the case items? If the answer of the above question is true , in that case synthesis tool will have to try to synthesize a gate level netlist that even with 'x' as input will be able to produce either a '0' or '1' in your second question. I need to understand the answer of the above question to underatand what you want to say.

Regards.

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#### lostinxlation

You are wrong here. I did not wrote or imply what you claimed. I wrote the tool will synthesize taking storage elements and combinational block such a circuit that will able to produce '0' or '1' with 'x' as input. However it may be difficult for you to realize such a circuit but I can visualize that.
Well, then show me the circuit. I have done full custom circuit design and can read the complicated transistor level circuit. Please show it to me. You do realize in real life, X is either 0 or 1, right ? So, I'm soooo curious to know how you differentiate the 0 or 1 represented as X and functional 0 and 1. Basically based on the behavior of the code, you would realize this truth table.
Very curious truth table to realize in the real circuit, isn't it ?

Code:
in      Y
---------
0       0
1       1
0(X)   0
1(X)   0

Does the synthesis tool take care of the properties of casex like even if the case items are unknown it will be able to produce the valid outputs against the case items? If the answer of the above question is true , in that case synthesis tool will have to try to synthesize a gate level netlist that even with 'x' as input will be able to produce either a '0' or '1' in your second question. I need to understand the answer of the above question to underatand what you want to say.
This question has been answered by someone else in the thread you started a few days ago. So, go and read it.

#### ASIC_int

Think of the circyit. It does not have anthing to do with transistor level. It is at gate level thinking.

2) what would be Y if in=x on the netlist generated from this RTL ?

How can it be available in google?

#### lostinxlation

Oh OK, I thought you were talking about case expression again. Sorry about that.
Answer to my 2nd question was answered in post #23 and that matches what the document claims, but went against what you believe.

So NOW can I see your circuit that you created to handle casex including X as an input, yet not output X ? I'm eagarly waiting for the circuit you mentioned.

#### ASIC_int

lostinxlation

See the circuit. The box is a positive level latch here with clock tied high.

What is post no. 23? Which document are u talikg of ?

#### Attachments

• gate.JPG
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#### lostinxlation

It's ..... a single MUX ? That's an excellent circuit to realize case statement. Not casex, though. But thanks for playing.

#### ASIC_int

lostinxlation

Look it carefully. It is a mux followed by a positive level latch whose clock input is tied to '1'. So I wrote 'box is a positive level latch here with clock tied high'.

Can u please provide what u are trying to mean by "But thanks for playing. "?

However I still did not get the answer of what you think to realize the circuit in your second question. Can u please let me know? Where is post no 23 to answer your circuit?

We do not find any direct answer from you. You always guide to something else like google, post no. 23 etc to answer your question.

Can you please read the following carefully again and answer me back.I do not find it to be answered in my earlier posts. Does the synthesis tool take care of the properties of casex like even if the case items are unknown it will be able to produce the valid outputs against the case items? If the answer of the above question is true , in that case synthesis tool will have to try to synthesize a gate level netlist that even with 'x' as input will be able to produce either a '0' or '1' in your second question. I need to understand the answer of the above question to underatand what you want to say.

Can u please let me know how casex is realized by synthesis tool to answer your statement "That's an excellent circuit to realize case statement. Not casex, though."

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#### ASIC_int

Hi lostinxlataion

I am eagerly waiting for your answer and justification for the second question.

Regards

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#### lostinxlation

Look it carefully. It is a mux followed by a positive level latch whose clock input is tied to '1'. So I wrote 'box is a positive level latch here with clock tied high'.
Latch with triggering pin tied to 1 ? Just a waste of logic, power and space.

I am eagerly waiting for your answer and justification for the second question.
It was answered in my past post.

A sincere response from me is done and no more beyond this point.

After seeing the logic with a mux and a "latch" you provided, my conclusion is that you are trolling.

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#### ASIC_int

lostinxlation

In post no. 27 you wrote ypou have answered the question in post no. 23. But everybody of us able to see you have not replied it in post no. 23.

Please do not make wrong claims. Can you point out where you have answered this.

We are not trolling. You should leave the habit of blaming people with no grounds. If you do not know try to learn more instead of bleming people.

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