Forum: FPGA, VHDL & Verilog fifo, ethernet

von Andrew W. (andrewwerner1)

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I am doing a project with a fifo in VHDL. Specifically I am trying to 
send 1024 bytes of data at a time through the fifo (and over ethernet). 
My input data width is 32 bits and my output data width is 8 bits. When 
hardwaring my write enable signal to a constant high and controlling 
when the fifo reads out data (when it has 1024 bytes of data), it seems 
to work fine. However, I am trying to use a square wave for the write 
enable signal and when I do this, the fifo outputs data for a short 
period of time and then stops. When trying to debug this problem I 
looked at the prog_full flag, write enable flag, empty flag, write 
acknowledge flag, and the write data count.

The result is that it seems the write data count stays at a constant 
value of 14 ("00000001110"). the write acknowledge signal is low which 
indicates the write command was unsuccessful.  However the write enable 
signal is a square wave as expected. Does anyone know whats going on? 
Thanks in Advance. Andy

von Na sowas (Guest)

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> with a fifo in VHDL
What architecture/toolchain?
Is this behaviour in simulation or in real hardware?
Wheres the fifo from? Self written or a fifo core?

von Andrew W. (andrewwerner1)

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It is a Xilinx board with a Virtex 5 FPGA

This behavior is in real hardware

the fifo is a fifo core (known as Fifo Generator by a company known as 


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