1 files changed, 60 insertions, 0 deletions
diff --git a/atk16_fpga/flash.v b/atk16_fpga/flash.v
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+++ b/atk16_fpga/flash.v
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+`timescale 1ns / 1ps
+
+// This is a memory model of the flash memory chip on the iCE40HX8K-EVB.
+// Relevant specs:
+// - 2MB space (not implemented entirely in simulation)
+// - An SPI interface
+module flash(
+    input wire cs,    // Chip select, active low
+    input wire clk,   // SPI clock
+    input wire mosi,  // Master Out Slave In
+    output reg miso,  // Master In Slave Out
+    input wire rst_n  // Active low reset
+);
+
+    reg [7:0] memory [0:2047];  // A smaller memory space for simplicity
+    reg [7:0] command;
+    reg [10:0] address;
+    reg [7:0] temp_data;
+    reg [3:0] bit_count;
+    reg write_enable;
+
+    always @(posedge clk or negedge rst_n) begin
+        if (!rst_n) begin
+            miso <= 1'b0;
+            command <= 8'b0;
+            address <= 11'b0;
+            temp_data <= 8'b0;
+            bit_count <= 4'b0;
+            write_enable <= 1'b0;
+        end else if (!cs) begin
+            if (bit_count < 8) begin
+                // First byte is the command
+                command[7 - bit_count] <= mosi;
+            end else if (bit_count < 19) begin
+                // Next 11 bits are the address
+                address[18 - bit_count] <= mosi;
+            end else if (command == 8'h02 && write_enable) begin
+                // Handle write command
+                if (bit_count < 28) begin
+                    temp_data[27 - bit_count] <= mosi;
+                    if (bit_count == 27) begin
+                        memory[address] <= temp_data;
+                    end
+                end
+            end else if (command == 8'h03) begin
+                // Handle read command
+                if (bit_count == 19) begin
+                    temp_data <= memory[address];
+                end
+                if (bit_count >= 20) begin
+                    miso <= temp_data[27 - bit_count];
+                end
+            end
+            bit_count <= bit_count + 1'b1;
+        end else begin
+            bit_count <= 0;
+            miso <= 1'bz; // Tristate when not active
+        end
+    end
+endmodule