// Copyright 2015, Brian Swetland <swetland@frotz.net>
// Licensed under the Apache License, Version 2.0.

`timescale 1ns / 1ps

`define WITH_CPU

module top(
	input clk12m_in,
	output [1:0]vga_r,
	output [1:0]vga_g,
	output [1:0]vga_b,
	output vga_hsync,
	output vga_vsync,
	input spi_mosi,
	output spi_miso,
	input spi_clk,
	input spi_cs,
	output out1,
	output out2
	);

wire clk12m;
wire clk25m;

assign out1 = clk12m;
assign out2 = clk25m;

pll_12_25 pll0(
	.clk12m_in(clk12m_in),
	.clk12m_out(clk12m),
	.clk25m_out(clk25m),
	.lock(),
	.reset(1'b1)
	);

wire sys_clk = clk12m;

reg cpu_reset = 1'b0;

// cpu memory interface
wire [15:0]ins_rd_addr;
wire [15:0]ins_rd_data;
wire ins_rd_req;

wire [15:0]dat_rw_addr;
wire [15:0]dat_rd_data;
wire dat_rd_req;
wire [15:0]dat_wr_data;
wire dat_wr_req;

`ifndef WITH_CPU
assign ins_rd_req = 1'b0;
assign dat_rd_req = 1'b0;
assign dat_wr_req = 1'b0;
assign ins_rd_addr = 16'd0;
assign dat_rw_addr = 16'd0;
`else
// fake arbitration that never denies a request
reg ins_rd_rdy = 1'b0;
reg dat_rd_rdy = 1'b0;
reg dat_wr_rdy = 1'b0;

always_ff @(posedge sys_clk) begin
	if (cpu_reset) begin
		ins_rd_rdy <= 1'b0;
		dat_rd_rdy <= 1'b0;
		dat_wr_rdy <= 1'b0;
	end else begin
		ins_rd_rdy <= ins_rd_req;
		dat_rd_rdy <= dat_rd_req;
		dat_wr_rdy <= dat_wr_req;
	end
end

// until arbitration works
assign dat_rd_data = 16'hEEEE;

cpu16 cpu(
	.clk(sys_clk),
	.ins_rd_addr(ins_rd_addr),
	.ins_rd_data(ins_rd_data),
	.ins_rd_req(ins_rd_req),
	.ins_rd_rdy(ins_rd_rdy),

	.dat_rw_addr(dat_rw_addr),
	.dat_wr_data(dat_wr_data),
	.dat_rd_data(dat_rd_data),
	.dat_rd_req(dat_rd_req),
	.dat_rd_rdy(dat_rd_rdy),
	.dat_wr_req(dat_wr_req),
	.dat_wr_rdy(dat_wr_rdy),

	.reset(cpu_reset)
	) /* synthesis syn_keep=1 */;
`endif

wire [15:0]dbg_waddr;
wire [15:0]dbg_wdata;
wire dbg_we;

spi_debug_ifc sdi(
	.spi_clk(spi_clk),
	.spi_cs_i(spi_cs),
	.spi_data_i(spi_mosi),
	.spi_data_o(spi_miso),
	.sys_clk(sys_clk),
	.sys_wr_o(dbg_we),
	.sys_waddr_o(dbg_waddr),
	.sys_wdata_o(dbg_wdata)
	);

// debug interface has priority over cpu writes
wire we = dbg_we | dat_wr_req;
wire [15:0]waddr = dbg_we ? dbg_waddr : dat_rw_addr;
wire [15:0]wdata = dbg_we ? dbg_wdata : dat_wr_data;

wire cs_sram = (waddr[15:12] == 4'h0);
wire cs_vram = (waddr[15:12] == 4'h8);
wire cs_ctrl = (waddr[15:12] == 4'hF);

always @(posedge sys_clk) begin
	if (cs_ctrl & we) begin
		cpu_reset <= wdata[0];
	end
end

//assign out1 = cpu_reset;
//assign out2 = cpu_raddr[0];
//assign out1 = dat_wr_req;
//assign out2 = dbg_we;

wire cs0r = ~ins_rd_addr[8];
wire cs1r = ins_rd_addr[8];
wire cs0w = ~waddr[8];
wire cs1w = waddr[8];

wire [15:0]rdata0;
wire [15:0]rdata1;

assign ins_rd_data = cs0r ? rdata0 : rdata1;

sram ram0(
	.clk(sys_clk),
	.raddr(ins_rd_addr),
	.rdata(rdata0),
	.re(ins_rd_req & cs0r & cs_sram),
	.waddr(waddr),
	.wdata(wdata),
	.we(we & cs0w & cs_sram)
	);

sram ram1(
	.clk(sys_clk),
	.raddr(ins_rd_addr),
	.rdata(rdata1),
	.re(ins_rd_req & cs1r & cs_sram),
	.waddr(waddr),
	.wdata(wdata),
	.we(we & cs1w & cs_sram)
	);

wire [1:0]vr, vg, vb;

vga40x30x2 vga(
	.clk25m(clk25m),
	.red(vr),
	.grn(vg),
	.blu(vb),
	.hs(vga_hsync),
	.vs(vga_vsync),
	.fr(),
	.vram_waddr(waddr[10:0]),
	.vram_wdata(wdata[7:0]),
	.vram_we(we & cs_vram),
	.vram_clk(sys_clk)
	);

// hack: flip display from blue to red when CPU is held in reset
assign vga_r = cpu_reset ? vb : vr;
assign vga_g = vg;
assign vga_b = cpu_reset ? vr : vb;

endmodule

module sram(
	input clk,
	input [15:0]raddr,
	output [15:0]rdata,
	input re,
	input [15:0]waddr,
	input [15:0]wdata,
	input we
	);

`ifndef uselatticeprim
reg [15:0]mem[255:0];
reg [15:0]ra;
always @(posedge clk) begin
	if (we)
		mem[waddr[7:0]] <= wdata;
	if (re)
		ra <= raddr;
end
assign rdata = mem[ra[7:0]];
`else
SB_RAM256x16 sram_inst(
	.RDATA(rdata),
	.RADDR(raddr[7:0]),
	.RCLK(clk),
	.RCLKE(1'b1),
	.RE(re),
	.WADDR(waddr[7:0]),
	.WDATA(wdata),
	.WCLK(clk),
	.WCLKE(1'b1),
	.WE(we),
	.MASK()
	);
`endif

endmodule