FIFO 是FPGA設計中最有用的模塊之一。FIFO 在模塊之間提供簡單的握手和同步機制，是設計人員將數據從一個模塊傳輸到另一個模塊的常用選擇。

在這篇文章中，展示了一個簡單的 RTL 同步 FIFO，可以直接在自己的設計中配置和使用它，該設計是完全可綜合的。

為什么要自己設計FIFO

那么，為什么呢？網上有很多關于 FIFO 的 Verilog/VHDL 代碼的資源，過去，我自己也使用過其中的一些。但令人沮喪的是，它們中的大多數都存在問題，尤其是在上溢出和下溢出條件下。所以想一勞永逸地解決這些問題。

FIFO 規格性能

同步，單時鐘。

基于寄存器的 FIFO，適用于中小型 FIFO。

Full、Empty、Almost-full、Almost-empty 標志。

完全可配置的數據寬度、深度和標志。

完全可綜合的系統 Verilog 代碼。

?

/*===============================================================================================================================
???Design???????:?Single-clock?Synchronous?FIFO

???Description??:?Fully?synthesisable,?configurable?Single-clock?Synchronous?FIFO?based?on?registers.
??????????????????-?Configurable?Data?width.
??????????????????-?Configurable?Depth.
??????????????????-?Configurable?Almost-full?and?Almost-empty?signals.?
===============================================================================================================================*/

module?my_fifo?#(
???????????????????parameter?DATA_W???????????=?4??????,????????//?Data?width
???????????????????parameter?DEPTH????????????=?8??????,????????//?Depth?of?FIFO???????????????????
???????????????????parameter?UPP_TH???????????=?4??????,????????//?Upper?threshold?to?generate?Almost-full
???????????????????parameter?LOW_TH???????????=?2???????????????//?Lower?threshold?to?generate?Almost-empty
????????????????)

????????????????(
???????????????????input???????????????????clk?????????,????????//?Clock
???????????????????input???????????????????rstn????????,????????//?Active-low?Synchronous?Reset
???????????????????
???????????????????input???????????????????i_wren??????,????????//?Write?Enable
???????????????????input??[DATA_W?-?1?:?0]?i_wrdata????,????????//?Write-data
???????????????????output??????????????????o_alm_full??,????????//?Almost-full?signal
???????????????????output??????????????????o_full??????,????????//?Full?signal

???????????????????input???????????????????i_rden??????,????????//?Read?Enable
???????????????????output?[DATA_W?-?1?:?0]?o_rddata????,????????//?Read-data
???????????????????output??????????????????o_alm_empty?,????????//?Almost-empty?signal
???????????????????output??????????????????o_empty??????????????//?Empty?signal
????????????????);


/*-------------------------------------------------------------------------------------------------------------------------------
???Internal?Registers/Signals
-------------------------------------------------------------------------------------------------------------------------------*/

logic?[DATA_W?-?1????????:?0]?data_rg?[DEPTH]?;????????//?Data?array
logic?[$clog2(DEPTH)?-?1?:?0]?wrptr_rg????????;????????//?Write?pointer
logic?[$clog2(DEPTH)?-?1?:?0]?rdptr_rg????????;????????//?Read?pointer
logic?[$clog2(DEPTH)?????:?0]?dcount_rg???????;????????//?Data?counter
??????
logic?????????????????????????wren_s??????????;????????//?Write?Enable?signal?generated?iff?FIFO?is?not?full
logic?????????????????????????rden_s??????????;????????//?Read?Enable?signal?generated?iff?FIFO?is?not?empty
logic?????????????????????????full_s??????????;????????//?Full?signal
logic?????????????????????????empty_s?????????;????????//?Empty?signal


/*-------------------------------------------------------------------------------------------------------------------------------
???Synchronous?logic?to?write?to?and?read?from?FIFO
-------------------------------------------------------------------------------------------------------------------------------*/
always?@?(posedge?clk)?begin

???if?(!rstn)?begin?????
??????????
??????data_rg???<=?'{default:?'0}?;
??????wrptr_rg??<=?0??????????????;
??????rdptr_rg??<=?0??????????????;??????
??????dcount_rg?<=?0??????????????;

???end

???else?begin

??????ready_rg?<=?1'b1?;
??????
??????/*?FIFO?write?logic?*/????????????
??????if?(wren_s)?begin??????????????????????????
?????????
?????????data_rg?[wrptr_rg]?<=?i_wrdata?;????????//?Data?written?to?FIFO

?????????if?(wrptr_rg?==?DEPTH?-?1)?begin
????????????wrptr_rg?<=?0???????????????;????????//?Reset?write?pointer??
?????????end

?????????else?begin
????????????wrptr_rg?<=?wrptr_rg?+?1????;????????//?Increment?write?pointer????????????
?????????end

??????end

??????/*?FIFO?read?logic?*/
??????if?(rden_s)?begin?????????

?????????if?(rdptr_rg?==?DEPTH?-?1)?begin
????????????rdptr_rg?<=?0???????????????;????????//?Reset?read?pointer
?????????end

?????????else?begin
????????????rdptr_rg?<=?rdptr_rg?+?1????;????????//?Increment?read?pointer????????????
?????????end

??????end

??????/*?FIFO?data?counter?update?logic?*/
??????if?(wren_s?&&?!rden_s)?begin???????????????//?Write?operation
?????????dcount_rg?<=?dcount_rg?+?1?;
??????end????????????????????
??????else?if?(!wren_s?&&?rden_s)?begin??????????//?Read?operation
?????????dcount_rg?<=?dcount_rg?-?1?;?????????
??????end

???end

end


/*-------------------------------------------------------------------------------------------------------------------------------
???Continuous?Assignments
-------------------------------------------------------------------------------------------------------------------------------*/

//?Full?and?Empty?internal
assign?full_s??????=?(dcount_rg?==?DEPTH)???1'b1?:?0?;
assign?empty_s?????=?(dcount_rg?==?0????)???1'b1?:?0?;

//?Write?and?Read?Enables?internal
assign?wren_s??????=?i_wren?&?!full_s????????????????;??
assign?rden_s??????=?i_rden?&?!empty_s???????????????;

//?Full?and?Empty?to?output
assign?o_full??????=?full_s??????????????????????????;
assign?o_empty?????=?empty_s?????????????????????????;

//?Almost-full?and?Almost?Empty?to?output
assign?o_alm_full??=?(dcount_rg?>?UPP_TH)???1'b1?:?0?;
assign?o_alm_empty?=?(dcount_rg?

	?

	基于 RAM 的 FIFO

	在上面的步驟中，我們看到了一個基于寄存器的同步FIFO。接下來，我們來看看基于 RAM 的 FIFO。該 FIFO 在 RAM 而不是寄存器上實現其數據陣列。這適用于在硬件上實現大型 FIFO ；特別是在 FPGA 上，FPGA 里有大量的Block RAM 可用。這將降低資源利用率，也可以獲得更好的時序性能。

	




	審核編輯：劉清