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Valued Contributor III
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Gate-level Simulation

Hi ,  

 

I am working on a design , it has a top level VHDL file ( a main state machine in it) and then a UART is enabled from this Main ( State machine ) . 

Everything works fine in RTL simulation . But when i switch to Gate-level Simulation i dont see any response or even glitch when UART is enabled . 

 

This is using Quartus-II ver 10.0 and Altera-Modelsim . 

 

When i compiled the design in Xilinx , again it failed in Gate-level but before shutting down it spite out a message about Modelsim couldnt handle 10K lines of code . 

 

Any clues ??? 

 

Thanks in advance.
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7 Replies
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Valued Contributor III
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Re: Gate-level Simulation

In Gate Level, UART signal are stable or do they have a x or z value? 

In Gate level the FSM signal are properly switching?
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Valued Contributor III
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Re: Gate-level Simulation

In Gate Level it wont start , not even show any glitch . Just stay dorment . 

I have traced the enable signal , it is valid but the UART State machine wont kick start .
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Valued Contributor III
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Re: Gate-level Simulation

What is that doesn't start? 

Modelsim? 

The Uart? 

The FSM? 

 

If Modelsim starts, do you see the input signal that switch? 

Do you see the outputs of the FSM that switch?
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Valued Contributor III
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Re: Gate-level Simulation

What is that doesn't start? 

Modelsim? 

The Uart? 

The FSM? 

 

 

ans: The UART  

 

Have a look at the screen shot of RTL and Gate Simulation.
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Valued Contributor III
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Re: Gate-level Simulation

the "gate" is the transmit start signal  

and "serial_out" is the serial data out signal .
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Valued Contributor III
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Re: Gate-level Simulation

So any clues why my gate-level isnt working ???

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Valued Contributor III
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Re: Gate-level Simulation

The RTL simulation screenshots you've posted don't cover the same time frame as the gate-level simuation screenshots. 

 

Also, I'd also suggest that you take a good look at the uut input and output signals, in order not to hide any missing connections 

For example, I don't a /tb_ssi/uut/clk signal in the simulations. I guess it's problably the same signal as one of the /tb_ssi/clk* signals, but I don't know which. 

 

This makes it impossible to compare your results.
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