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Observer matttay
Observer
1,183 Views
Registered: ‎01-13-2010

Fifo Write Data Count == 2 after reset

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Hi, I used Vivado 14.7 and Fifo Generator 13.2 to generate native fifo, independent clocks BRAM, FWFT, 32bits r/w, 2048 words deep, reset pin, reset sync enabled, async reset, safety circuit,more accurate data counts. The fifo is for independent clocks, but right now the read/write clocks are the same clock

 

Both sim and actual hardware show the same: After a manual reset of the fifo, the write data count is 2 always. Why is that? Even in sim, where I can watch it come out of reset and ensure there's nothing going on the write enable I see this. The fifo works as I expect aside from this. Am I missing something fundamental? 

 

Thanks

 

 

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Observer matttay
Observer
1,320 Views
Registered: ‎01-13-2010

Re: Fifo Write Data Count == 2 after reset

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The answer to my question is in table 3-3 of the Fifo Generator doc PG057. This table shows that when read/write width ratio is 1:1 and More Accurate Data Count is enabled, then the empty fifo wr_data_count is 2. In other words, you NEVER will see the fifo report 0. 

 

Thus, the behavior is expected. 

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3 Replies
Moderator
Moderator
1,145 Views
Registered: ‎08-08-2017

Re: Fifo Write Data Count == 2 after reset

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Hi @matttay

 

I believe you are using VIVADO 2017.4  (VIVADO 2014.7 is not exist). Please share the ILA capture depicting this 

behavior.

I will check the simulation at my end with the settings you have mentioned ,but it will be useful if you share the .xci to check the other 

parameters i.e Synchronization stages, ECC , output register  options .

 

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Observer matttay
Observer
1,321 Views
Registered: ‎01-13-2010

Re: Fifo Write Data Count == 2 after reset

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The answer to my question is in table 3-3 of the Fifo Generator doc PG057. This table shows that when read/write width ratio is 1:1 and More Accurate Data Count is enabled, then the empty fifo wr_data_count is 2. In other words, you NEVER will see the fifo report 0. 

 

Thus, the behavior is expected. 

View solution in original post

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Moderator
Moderator
1,139 Views
Registered: ‎08-08-2017

Re: Fifo Write Data Count == 2 after reset

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Hi @matttay

 

Thank you for pointing this out.

Please mark your answer as accepted solution to close this thread.

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