FIFO Generator

A FIFO can be created using the FIFO generator. (Andrew recommends using XPM but I forget how to do that). Here is a TCL excerpt which does it. I normally use the First_Word_Fall_Through option. This results in the following behavior:

• EMPTY='0', data appears at output and VALID='1' on second rising edge after WR_EN sampled high.
• EMPTY='1', VALID='0' on rising edge with RD_EN='1'. No data is transferred.
• FULL='1' on rising edge where last data word is accepted with WR_EN='1'.
• FULL='0' on rising edge with RD_EN='1', data updates to next word
• VALID='1' continuously unless EMPTY='1'

The odd thing here is that an extra read attempt is required to make the EMPTY flag come on.

Without First_Word_Fall_Through option:

• EMPTY='0' immediately on rising edge with WR_EN='1' (not data out or VALID change
• VALID='1' for one clock when RD_EN='1'
• EMPTY='1' on rising edge with RD_EN='1', VALID='1' for one clock overlapping EMPTY.

Neither of these is ideal; one would prefer EMPTY to come on immediately when last word is read in the FWFT mode.

TCL to create FIFO

create_project -force dummy -part xc7a35t-cpg236-1
create_ip -name fifo_generator \
    -vendor xilinx.com \
    -library ip \
    -version 13.2 \
    -module_name ${name} \
    -dir ${output_path}
set_property \
    -dict [list \
	       CONFIG.Valid_Flag {true} \
	       CONFIG.Performance_Options {First_Word_Fall_Through} \
	       CONFIG.Input_Data_Width {8} \
	       CONFIG.Input_Depth {16} \
	       CONFIG.Output_Data_Width {8} \
	       CONFIG.Output_Depth {16} \
	       CONFIG.Data_Count_Width {5} \
	       CONFIG.Write_Data_Count_Width {5} \
	       CONFIG.Read_Data_Count_Width {5} \
	       CONFIG.Full_Threshold_Assert_Value {15} \
	       CONFIG.Full_Threshold_Negate_Value {14}] \
    [get_ips ${name}]

generate_target {instantiation_template} [get_files ${xci_path}]
generate_target all [get_files ${xci_path}]
export_ip_user_files -of_objects [get_files ${xci_path}] -no_script -sync -force -quiet
create_ip_run [get_files -of_objects [get_filesets sources_1] ${xci_path}]
launch_runs fifo_512x36_synth_1
wait_on_run fifo_512x36_synth_1
close_project