Intel® Quartus® Prime Pro Edition User Guide: Partial Reconfiguration

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ID 683834
Date 1/11/2022
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2.7.10. Implementing Clock Enable for On-Chip Memories with Initialized Contents

Follow these guidelines to implement clock enable for on-chip memories with initialized contents:
  1. To avoid spurious writes during PR programming for memories with initialized contents, implement the clock enable circuit in the same PR region as the M20K or MLAB RAM. This circuit depends on an active-high clear signal from the static region.
  2. Before you begin the PR programming, assert this signal to disable the memory’s clock enable. Your system PR controller must deassert the clear signal on PR programming completion. You can use the freeze signal for this purpose.
  3. Use the Intel® Quartus® Prime IP Catalog or Platform Designer to instantiate the On-Chip Memory and RAM Intel® FPGA IP cores that include an option to automatically add this circuitry.
Figure 29. RAM Clock Enable Circuit for PR Region

Verilog RTL for Clock Enable

   reg ce_reg;
    reg [1:0] ce_delay;

    always @(posedge clock, posedge freeze) begin
        if (freeze) begin
            ce_delay <= 2'b0;
        end
        else begin
            ce_delay <= {ce_delay[0], 1'b1};
        end
    end

    always @(posedge clock, negedge ce_delay[1]) begin
        if (~ce_delay[1]) begin
            ce_reg <= 1'b0;
        end
        else begin
            ce_reg <= clken_in;
        end
    end

    wire ram_wrclocken;
    assign ram_wrclocken = ce_reg;

VHDL RTL for Clock Enable

ENTITY mem_enable_vhd IS PORT(
        clock      : in  std_logic;
        freeze  : in  std_logic;
		clken_in : in std_logic;
        ram_wrclocken : out std_logic);
END mem_enable_vhd;

ARCHITECTURE behave OF mem_enable_vhd is
	SIGNAL ce_reg: std_logic;
	SIGNAL ce_delay: std_logic_vector(1 downto 0);
BEGIN
PROCESS (clock, freeze)
BEGIN
	IF ((clock'EVENT AND clock = '1') or (freeze'EVENT AND freeze = '1')) THEN
		IF (freeze = '1') THEN
			ce_delay <= "00";
		ELSE
			ce_delay <= ce_delay(0) & '1';
		END IF;
	END IF;
	
END PROCESS;

PROCESS (clock, ce_delay(1))
BEGIN
	IF ((clock'EVENT AND clock = '1') or (ce_delay(1)'EVENT AND ce_delay(1) = '0')) THEN
		IF (ce_delay(1) = '0') THEN
			ce_reg <= '0';
		ELSE
			ce_reg <= clken_in;
		END IF;
	END IF;
	
END PROCESS;

ram_wrclocken <= ce_reg;

END ARCHITECTURE behave;

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