== 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
}}}