AHB总线读写RAM

timescale 1ns/1psmodule ahb2ram #(parameter ADDR_BITS 32) (input resetn,input ahb_clock,input [1:0] ahb_htrans,//传输类型00idle, 01:busy, 10:NONSEQ, 11:SEQ NONSEQ新数据 SEQ:连续传输 IDLE:空闲 BUSY:忙input [2:0] ahb_hsize,input [31:0] ahb_hwdata,input [31:0] ahb_haddr,input ahb_hwrite,output reg [31:0] ahb_hrdata,output reg ahb_hreadyout,output [ADDR_BITS-3:0] ram_addr,output reg [3:0] ram_byteena,output [31:0] ram_data,output reg ram_wren,output ram_rden,input [31:0] ram_q);// All AHB signals assume 1 cycle latency from RAM (no output register)//写时序说明//1. 在 T0 上升沿// - 主机驱动地址 HADDR// - 设置 HTRANS NONSEQ// - 设置 HWRITE 1// - 从机在该上升沿采样地址与控制信号////2. 在 T1 上升沿// - 主机驱动写数据 HWDATA// - 从机在 HREADY1 的情况下采样 HWDATA// - 若 HREADY0主机必须保持所有信号不变////3. 若 HREADY0// - 主机在后续每个时钟周期保持// HADDR / HTRANS / HWRITE / HWDATA// - 直到从机拉高 HREADY// - 在 HREADY1 的上升沿写数据被正式采样reg [ADDR_BITS-1:0] haddr_reg;reg [2:0] hsize_reg;reg [31:0] ram_qd;reg rd_en_d1;//打拍reg rd_en_d2;//采样ram_qreg rd_en_d3;//驱动HRDATA//AHB读数据 NONSEQ / SEQ//在AHB读操作中,RAM 具有1拍读延迟而从机必须在 HREADY1 的那一拍提供有效的 HRDATA//因此需要在读开始时拉低 ahb_hreadyout插入一拍等待使 RAM 读数据与 AHB 数据阶段对齐wire rd_en !ahb_hwrite (ahb_htrans[1] || !ahb_hreadyout);always (posedge ahb_clock or negedge resetn) beginif (!resetn) beginram_byteena 4’b1111;end else if (ahb_htrans[1] ahb_hwrite) beginif (ahb_hsize 3’b000) begin // byte writecase(ahb_haddr[1:0])2’b00: ram_byteena 4’b0001;2’b01: ram_byteena 4’b0010;2’b10: ram_byteena 4’b0100;2’b11: ram_byteena 4’b1000;default: ram_byteena 4’hX;endcaseend else if (ahb_hsize 3’b001) begin // halfword writecase (ahb_haddr[1])1’b0: ram_byteena 4’b0011;1’b1: ram_byteena 4’b1100;default:ram_byteena 4’hX;endcaseend else begin // word (including above) writeram_byteena 4’b1111;endendendalways (posedge ahb_clock or negedge resetn) beginif (!resetn) beginhsize_reg 3’b0;end else if (ahb_htrans[1]) beginhsize_reg ahb_hsize;endendalways (posedge ahb_clock or negedge resetn) beginif (!resetn)ram_wren 0;else if (ahb_htrans[1] ahb_hwrite)ram_wren 1;elseram_wren 0;endalways (posedge ahb_clock or negedge resetn) beginif (!resetn)haddr_reg 0;else if (ahb_htrans[1] ahb_hwrite ahb_hreadyout)haddr_reg ahb_haddr[ADDR_BITS-1:0];else if (ahb_htrans 2’b10 !ahb_hwrite ahb_hreadyout)haddr_reg ahb_haddr[ADDR_BITS-1:0];else if (ahb_htrans 2’b11 !ahb_hwrite rd_en_d1)haddr_reg haddr_reg (1 hsize_reg);endalways (posedge ahb_clock or negedge resetn) beginif (!resetn) beginrd_en_d1 0;rd_en_d2 0;rd_en_d3 0;end else beginrd_en_d1 rd_en;rd_en_d2 rd_en_d1;rd_en_d3 rd_en_d2;endendalways (posedge ahb_clock or negedge resetn) beginif (!resetn)ahb_hreadyout 1;else if (rd_en !rd_en_d1)//第一个上升沿ahb_hreadyout 0;else if (rd_en_d3 rd_en_d2)//ahb_hreadyout 1;endalways (posedge ahb_clock or negedge resetn) beginif (!resetn)ahb_hrdata 0;else if (rd_en_d3)ahb_hrdata ram_qd;endalways (posedge ahb_clock or negedge resetn) beginif (!resetn)ram_qd 0;else if (rd_en_d2)ram_qd ram_q;endassign ram_addr haddr_reg[ADDR_BITS-1:2];assign ram_data ahb_hwdata;assign ram_rden rd_en_d1;endmodule