SDRAM刷新状态机设计程序——仅供参考
/*---------------------------------------------------模块名称 ： AUTO REFRESH(自动刷新模块)非背靠背刷新
模块说明 ： tRP(min)=15nstRFC(min)=66ns
--2015-10-06
--------------------------------------------------*/
`include "sdram_head.v"
module sdr_ref_fsm(sys_clk, rst_n, ref_done, ref_bus);
input sys_clk;
input rst_n; //刷新模块启动信号
output reg ref_done;//刷新完成标志信号
output reg ref_bus;
localparam s0 = 2'b00;
localparam s1 = 2'b01;
localparam s2 = 2'b10;
reg count;//延时计数器
reg state;
always @ (posedge sys_clk)
begin
if (!rst_n)
begin
ref_bus <= `NOP;//cs_ras_cas_we_cke_ba_a
ref_bus <= 1;
ref_bus <= 0;
ref_done <= 0;
count <= 3'd0;
state <= s0;
end
else
case (state)
s0 :begin
ref_bus <= `PRECHANGE; //置位后立刻发送预充电命令
ref_bus <= 1; //选择所有bank
state <= s1;
end
s1 : begin //从S1到S2已经经过了一拍，所以这里`tRP-1
ref_bus <= `NOP;
if (count < `tRP-1)
count <= count + 1'b1;
else
begin
count <= 0;
state <= s2;
ref_bus <= `REFRESH; //发送自动刷新命令
end
end
s2 : begin
ref_bus <= `NOP;
if(count < `tRFC-1)
count <= count + 1'b1;
else
begin
ref_done <= 1; //刷新过程全部完成，输出标志信号
end
end
default : ref_bus <= `NOP;
endcase
end
endmodule
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