写模块跟着视频看了一个多星期，一开始始终有点弄不清楚，现在记录一下理解的过程。
阅读文档信息：
首先阅读文档信息，了解SDRAM写过程的状态转换和时序图
SDRAM整体状态流程如图所示：
在SDRAM整体系统中，若要进入写模块，则需要从idle状态首先激活一行（row_acttive），再进入写状态（write），发送precharge命令跳出写状态。
WRITEA 状态不使用，因为当处于 WRITEA 状态时，它会自动的进入到 Precharge 状态。想要继续进行写操作就要先再次激活行，也就是说 WRITEA 比在 WRITE 状态的工作效率要低很多。
SDRAM写模块时序图如图所示：
观察时序图可知，在发送active命令时同时发送A0-A12,BANK信息,其中A0-A12指定了行信息，也就是说在ACT命令（激活状态）下，确定了要写入数据的行（SDRAM的数据是一行一行的写），BANK命令确定了要写入数据的SDRAM的块。也就是说在ACT命令下已经确定了bank和row；经过tRCD（至少20ns）时间后，再能发送write命令，发送write命令的同时也发送col命令（col命令也通过A0-A9发送，此时A10为低电平），也同时发送bank命令和数据。设置突发长度为4，等待4个周期的时间写入数据，才可以进行precharge命令退出写模式。
SDRAM写模块状态如图所示（写模块内部状态转移，与SDRAM整体的状态无关）：
dle，w_req状态承接上下部分，接收到来自顶层模块的写触发信号（w_trig）后，由idle状态到w_req，此时w_req状态向顶层模块发送req信号，接收到写使能（w_en ）信号后进入到act状态，此时也接收到row地址和bank地址信息。由时序图可知经过20ns后进入write状态。在write状态下，当数据写完或者刷新时间到的时候或者指定的行数据写完的时候，需要跳出write状态，此时进入pre状态。在pre状态下，数据写完进入idle状态；当刷新请求来的时候要进行刷新，在顶层模块的设计下刷新结束后会进入仲裁模块，此时需要重新发送写请求，接收到写使能；在指定的一行写完后需要重新激活，此时不需要外部的写使能信号再传输进来。
写模块代码如下：
其中burst_cnt用来计数突发长度，write->pre状态，break_cnt用来计数从pre->act状态（至少20ns）
module sdram_wirte(
input sclk ,
input srst ,
//communicate with top
input w_en ,
output wire w_req ,
output reg flag_w_end ,
//
input ref_req ,
input w_trig ,
//write interface
output reg [3:0] w_cmd ,
output reg [11:0] w_addr ,
output wire [1:0] bank_addr,
output reg [15:0] w_data
);
//==========================================================
//======= define parameter and internal signal ========
//==========================================================
//define state
localparam s_idle = 5'b00001;
localparam s_req = 5'b00010;
localparam s_act = 5'b00100;
localparam s_wr = 5'b01000;
localparam s_pre = 5'b10000;
//
localparam cmd_nop = 5'b0111;
localparam cmd_pre = 5'b0010;
localparam cmd_ref = 5'b0001;
localparam cmd_act = 5'b0011;
localparam cmd_wr = 5'b0100;
reg flag_wr;
reg[4:0] state;
reg flag_act_end;
reg flag_pre_end;
reg sd_row_end;
reg[1:0] burst_cnt;
reg[1:0] burst_cnt_t;
reg wr_data_end;
reg[3:0] act_cnt;
reg[3:0] break_cnt;
reg[6:0] col_cnt;
reg[11:0] row_addr;
wire[8:0] col_addr;
//==========================================================
//==================== main code ====================
//==========================================================
//flag_wr
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
flag_wr <= 1'b0;
else if(w_trig == 1'b1 &&flag_wr == 1'b0)
flag_wr <= 1'b1;
else if(wr_data_end == 1'b1)
flag_wr <= 1'b0;
end
// w_cmd
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
w_cmd <= cmd_nop;
else case(state)
s_act:
if(act_cnt == 'd0)
w_cmd <= cmd_act;
else
w_cmd <= cmd_nop;
s_wr:
if(burst_cnt == 'd0)
w_cmd <= cmd_wr;
else
w_cmd <= cmd_nop;
s_pre:
if(break_cnt == 'd0)
w_cmd <= cmd_pre;
else
w_cmd <= cmd_nop;
default:w_cmd <= cmd_nop;
endcase
end
//burst_cnt
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
burst_cnt <= 'd0;
else if(state == s_wr)
burst_cnt <= burst_cnt + 1'b1;
else
burst_cnt <= 'd0;
end
//burst_cnt
always@(posedge sclk )begin
burst_cnt_t <= burst_cnt;
end
//state
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
state <= s_idle;
else case(state)
s_idle:
if(w_trig == 1'b1)
state <= s_req;
else
state <= s_idle;
s_req:
if(w_en == 1'b1)
state <= s_act ;
else
state <= s_req;
s_act:
if(flag_act_end == 1'b1)
state <= s_wr;
else
state <= s_act;
s_wr:
if(wr_data_end == 1'b1)
state <= s_pre;
else if(ref_req == 1'b1 && burst_cnt_t == 'd3 &&flag_wr == 1'b1)
state <= s_pre;
else if(sd_row_end == 1'b1 && flag_wr == 1'b1)
state <= s_pre;
s_pre:
if(ref_req == 1'b1 && flag_wr == 1'b1)
state <= s_req;
else if(flag_pre_end == 1'b1 &&flag_wr == 1'b1)
state <= s_act;
else if(wr_data_end == 1'b1)
state <= s_idle;
default:state <= s_idle;
endcase
end
//flag_act_end
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
flag_act_end <= 1'b0;
else if (act_cnt == 'd3) // 3?
flag_act_end <= 1'b1;
else
flag_act_end <= 1'b0;
end
//flag_pre_end
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
flag_pre_end <= 1'b0;
else if (break_cnt == 'd3)
flag_pre_end <= 1'b1;
else
flag_pre_end <= 1'b0;
end
//break_cnt
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
break_cnt <= 'd0;
else if(state == s_pre)
break_cnt <= break_cnt +1'b1;
else
break_cnt <= 'd0;
end
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
wr_data_end <= 'd0;
else if(row_addr == 'd1 && col_addr == 'd511)\
wr_data_end <= 1'b1;
else
wr_data_end <= 1'b0;
end
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
col_cnt <= 'd0;
else if(col_addr == 'd511)
col_cnt <= 'd0;
else if(burst_cnt_t == 'd3)
col_cnt <= col_cnt + 1'b1;
end
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
row_addr <= 'd0;
else if(sd_row_end == 1'b1)
row_addr <= row_addr +'b1;
end
//w_addr
always@(*)begin
case(state)
s_act:
if(act_cnt == 'd0)
w_addr <= row_addr;
s_wr:
w_addr <= {3'b000,col_addr};
s_pre:
if(break_cnt == 'd0)
w_addr <= {12'b0100_0000_0000};
endcase
end
always@(posedge sclk or negedge srst )begin
if(srst == 1'b0)
sd_row_end <= 1'b0;
else if(col_addr == 'd510)
sd_row_end <= 1'b1;
else
sd_row_end <= 1'b0;
end
always@(posedge sclk or negedge srst )begin
if(srst == 1'b0)
flag_w_end <= 1'b0;
else if((state == s_pre && ref_req == 1'b1)
|| (state == s_pre && wr_data_end == 1'b1))
flag_w_end <= 1'b1;
else
flag_w_end <= 1'b0;
end
assign bank_addr = 2'b00;
assign col_addr = {col_cnt,burst_cnt_t};
assign w_req = state[1];
//产生测试数据
always@(*)begin
case(burst_cnt_t):
0: w_data <= 'd3;
1: w_data <= 'd5;
2: w_data <= 'd7;
3: w_data <= 'd9;
endcase
end
endmodule顶层模块代码：
在测试中添加了一个w_trig信号
疑问：实际上w_trig信号如何产生？fpga input？按下按键？
module sdram_top(
input sclk,
input srst,
//sdram interface
output wire sdram_clk,
output wire sdram_cke,
output wire sdram_cs_n,
output wire sdram_cas_n,
output wire sdram_ras_n,
output wire sdram_we_n,
output wire [1:0] sdram_bank,
output reg [11:0] sdram_addr,
output wire [1:0] sdram_dqm,
inout [15:0] sdram_dq,
//
input w_trig
);
//==========================================================
//======= define parameter and internal signal ========
//==========================================================
//define state machine
reg [4:0] state;
localparam idle = 5'b00001;
localparam arbit = 5'b00010;
localparam aref = 5'b00100;
localparam write = 5'b01000;
localparam read = 5'b10000;
//init module
reg[3:0] sd_cmd;
wire flag_init_end;
wire [3:0] init_cmd;
wire [11:0] init_addr;
//refresh module
reg ref_en;
wire ref_req;
wire flag_ref_end;
wire [3:0] cmd_reg;
wire [11:0] ref_addr;
//write module
reg w_en ;
wire w_req ;
wire flag_w_end;
wire[3:0] w_cmd ;
wire[11:0] w_addr ;
wire[1:0] w_bank_addr;
wire[15:0] w_data;
//==========================================================
//==================== main code ====================
//==========================================================
always@(posedge sclk or negedge srst) begin
if(srst == 1'b0)
state <= idle;
else
case(state)
idle:
if(flag_init_end == 1'b1)
state <= arbit;
else
state <= idle;
arbit:
if(ref_en == 1'b1)
state <= aref;
else if(w_en == 1'b1)
state <= write;
else
state <= arbit;
aref:
if(flag_ref_end == 1'b1)
state <= arbit;
else
state <= aref;
write:
if(flag_w_end == 1'b1)
state <= arbit;
else
state <= write;
default:
state <= idle;
endcase
end
always@(*)
begin
case(state)
idle:
begin
sd_cmd <= init_cmd;
sdram_addr <= init_addr;
end
aref:
begin
sd_cmd <= cmd_reg;
sdram_addr <= ref_addr;
end
write:
begin
sd_cmd <= w_cmd;
sdram_addr <= w_addr;
end
default:begin
sd_cmd <= 4'b0111;//nop
sdram_addr <= 'd0;
end
endcase
end
//ref_en
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
ref_en <= 1'b0;
else if(state == arbit && ref_req == 1'b1)
ref_en <= 1'b1;
else
ref_en <= 1'b0;
end
//w_en
always@(posedge sclk or negedge srst)begin
if(srst == 1'b0)
w_en <= 1'b0;
else if(state == arbit && ref_en == 1'b0 && w_req == 1'b1)
w_en <= 1'b1;
else
w_en <= 1'b0;
end
assign sdram_cke = 1'b1;
//assign sdram_addr = (state == idle) ?init_addr:ref_addr;
//assign {sdram_cs_n, sdram_ras_n, sdram_cas_n, sdram_we_n} = (state == idle) ?init_cmd:cmd_reg;
assign {sdram_cs_n, sdram_ras_n, sdram_cas_n, sdram_we_n} = sd_cmd;
assign sdram_dqm = 2'b00;
assign sdram_clk = ~sclk; //内部时钟上升沿采集命令，命令又是由系统时钟上升沿产生的？？（为了保证采样时刻处在数据中间时刻）
assign sdram_dq = (state == write)?w_data:{16{1'bz}};
assign sdram_bank = (state == write)?w_bank_addr:2'b00;
sdram_init sdram_init_inst(
.sclk (sclk) ,
.srst (srst) ,
.cmd_reg (init_cmd) ,
.sdram_addr (init_addr) ,
.flag_init_end (flag_init_end)
);
sdram_aref sdram_aref(
.sclk (sclk),
.srst (srst),
//commmunicate with arbit
.ref_en (ref_en),
.ref_req (ref_req),
.flag_ref_end (flag_ref_end),
//others
.flag_init_end (flag_init_end),
.cmd_reg (cmd_reg),
.ref_addr (ref_addr)
);
sdram_wirte sdram_wirte_inst(
.sclk (sclk),
.srst (srst),
//communicate with top
.w_en (w_en ),
.w_req (w_req ),
.flag_w_end (flag_w_end),
//
.ref_req (ref_req),
.w_trig (w_trig ),
//write interface
.w_cmd (w_cmd ),
.w_addr (w_addr ),
.bank_addr (w_bank_addr ),
.w_data (w_data)
);
endmodule测试代码：
`timescale 1ns/1ns
module tb_sdram_top;
reg sclk;
reg srst;
//----------------------------------------
wire sdram_clk;
wire sdram_cke;
wire sdram_cs_n;
wire sdram_cas_n;
wire sdram_ras_n;
wire sdram_we_n;
wire [1:0] sdram_bank;
wire [11:0] sdram_addr;
wire [1:0] sdram_dqm;
wire [15:0] sdram_dq;
reg w_trig;
//----------------------------------------
initial begin
w_trig <= 0;
#205000
w_trig <= 'b1;
#20
w_trig <= 'b0;
end
initial begin
sclk <= 1;
srst <= 0;
#100
srst <=1;
end
always #10 sclk <= ~sclk;
defparam sdram_model_plus_inst.addr_bits = 12;
defparam sdram_model_plus_inst.data_bits = 16;
defparam sdram_model_plus_inst.col_bits = 9;
defparam sdram_model_plus_inst.mem_sizes = 2*1024*1024;//1 M
sdram_top sdram_top_inst(
.sclk (sclk ),
.srst (srst ),
.sdram_clk (sdram_clk ),
.sdram_cke (sdram_cke ),
.sdram_cs_n (sdram_cs_n ),
.sdram_cas_n (sdram_cas_n),
.sdram_ras_n (sdram_ras_n),
.sdram_we_n (sdram_we_n ),
.sdram_bank (sdram_bank ),
.sdram_addr (sdram_addr ),
.sdram_dqm (sdram_dqm ),
.sdram_dq (sdram_dq ),
.w_trig (w_trig)
);
sdram_model_plus sdram_model_plus_inst(
.Dq (sdram_dq) ,
.Addr (sdram_addr),
.Ba (sdram_bank),
.Clk (sdram_clk),
.Cke (sdram_cke),
.Cs_n (sdram_cs_n),
.Ras_n (sdram_ras_n),
.Cas_n (sdram_cas_n),
.We_n (sdram_we_n),
.Dqm (sdram_dqm),
.Debug (1'b1)
);
endmodule
