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Voyager
Voyager
4,628 Views
Registered: ‎10-21-2015

When is ALMOSTEMPTY of FIFO36E1 signal active?

Hi,

 

I use FIFO36E1 in which FIRST_WORD_FALL_THROUGH is TRUE.

If ALMOST_EMPTY_OFFSET is 15, is ALMOSTEMPTY signal active when the number of data words remained in fifo including current dout  is 15 or 16?

 

Thanks in advance

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3 Replies
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Voyager
Voyager
4,611 Views
Registered: ‎10-21-2015

My simulation result is 14. Is there anything wrong in my code?

.......

rdata= 495, rden = 1, empty = 0
rdata= 496, rden = 1, empty = 0
rdata= 497, rden = 1, empty = 0
rdata= 498, rden = 1, empty = 0
rdata= 499, rden = 1, empty = 0
rdata= 500, rden = 1, empty = 1
rdata= 501, rden = 1, empty = 1
rdata= 502, rden = 1, empty = 1
rdata= 503, rden = 1, empty = 1
rdata= 504, rden = 1, empty = 1
rdata= 505, rden = 1, empty = 1
rdata= 506, rden = 1, empty = 1
rdata= 507, rden = 1, empty = 1
rdata= 508, rden = 1, empty = 1
rdata= 509, rden = 1, empty = 1
rdata= 510, rden = 1, empty = 1
rdata= 511, rden = 1, empty = 1
rdata= 512, rden = 1, empty = 1
rdata= 513, rden = 1, empty = 1
rdata= 513, rden = 1, empty = 1
rdata= 513, rden = 1, empty = 1

.....

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Xilinx Employee
Xilinx Employee
4,610 Views
Registered: ‎09-20-2012

Hi @hokim

 

If ALMOST_EMPTY_OFFSET is 15, then the ALMOST_EMPTY flag will get asserted when the number of words left in FIFO is 15.

Thanks,
Deepika.
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Voyager
Voyager
4,593 Views
Registered: ‎10-21-2015

Thanks for your reply,

My point is that the words left in FIFO include or not current DO in FWFT(FIRST_WORD_FALL_THROUGH) mode. 

At first, I thought the words left in FIFO of FWFT includes DO. 

So I thought the following code has wrong ALMOST_EMPTY_OFFSET and it shoul be 'h10 not 'hf

 https://github.com/pavel-demin/red-pitaya-notes/blob/master/cores/ axis_ram_writer_v1_0/axis_ram_writer.v

But the code works well on fpga. So I guess  FWFT doesn't include DO.

 

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