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// Wishbone module for spi communications with an SD Card
// The programming interface is simple --
// Write the desired clock divider to address 1 (should be 1 or higher)
// Status is in address 0. A 1 indicates the last transaction is done and it is safe to
// send another
// Writing a byte to address 2 sends that byte over SPI. When it is done,
// status (addr 0) goes high again, and the received byte can be read from address 3.
module sd_spi_wb
(input clk,
input rst,
// SD Card interface
output sd_clk,
output sd_csn,
output sd_mosi,
input sd_miso,
input wb_cyc_i,
input wb_stb_i,
input wb_we_i,
input [1:0] wb_adr_i,
input [7:0] wb_dat_i,
output reg [7:0] wb_dat_o,
output reg wb_ack_o);
localparam ADDR_STATUS = 0;
localparam ADDR_CLKDIV = 1;
localparam ADDR_WRITE = 2;
localparam ADDR_READ = 3;
wire [7:0] status, rcv_dat;
reg [7:0] clkdiv;
wire ready;
reg ack_d1;
reg cs_reg;
assign sd_csn = ~cs_reg; // FIXME
always @(posedge clk)
if(rst) ack_d1 <= 0;
else ack_d1 <= wb_ack_o;
always @(posedge clk)
if(rst) wb_ack_o <= 0;
else wb_ack_o <= wb_cyc_i & wb_stb_i & ~ack_d1;
always @(posedge clk)
case(wb_adr_i)
ADDR_STATUS : wb_dat_o <= {7'd0,ready};
ADDR_CLKDIV : wb_dat_o <= clkdiv;
ADDR_READ : wb_dat_o <= rcv_dat;
default : wb_dat_o <= 0;
endcase // case(wb_adr_i)
always @(posedge clk)
if(rst)
begin
clkdiv <= 200;
cs_reg <= 0;
end
else if(wb_we_i & wb_stb_i & wb_cyc_i & wb_ack_o)
case(wb_adr_i)
ADDR_STATUS : cs_reg <= wb_dat_i;
ADDR_CLKDIV : clkdiv <= wb_dat_i;
endcase // case(wb_adr_i)
wire go = wb_we_i & wb_stb_i & wb_cyc_i & wb_ack_o & (wb_adr_i == ADDR_WRITE);
sd_spi sd_spi(.clk(clk),.rst(rst),
.sd_clk(sd_clk),.sd_mosi(sd_mosi),.sd_miso(sd_miso),
.clk_div(clkdiv),.send_dat(wb_dat_i),.rcv_dat(rcv_dat),
.go(go),.ready(ready) );
endmodule // sd_spi_wb
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