9086/system/memory.v

/* memory.v - implementation of memory external to the 9086 CPU for testing purposes

   This file is part of the 9086 project.

   Copyright (c) 2023 Efthymios Kritikos

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/* This warning is because we don't use the full address bus. */
/* verilator lint_off UNUSEDSIGNAL */
module doublemem(input [19:0] address,output [15:0] cpu_read_data ,input [15:0] cpu_write_data,input rd,input wr,input BHE,input cs);
/* verilator lint_on UNUSEDSIGNAL */

reg [15:0] memory [0:32768];

initial begin
`ifndef YOSYS
	string boot_code;
	if(!$value$plusargs("BOOT_CODE=%s",boot_code))begin
		$display("No boot code specified. Please add +BOOT_CODE=<path> to your vvp args");
		$finish;
	end
	$readmemh(boot_code, memory,0,32767);
`else
	//TODO: don't have it hard coded
	$readmemh("boot_code.txt", memory,0,32767);
`endif
end

assign cpu_read_data[7:0] = !address[0:0] & !rd & !cs ? memory[address[16:1]][15:8]  : 8'hz;

assign cpu_read_data[15:8] =     !BHE     & !rd & !cs ? memory[address[16:1]][7:0]   : 8'hz;

always @(negedge wr) begin
	if( cs == 0 ) begin
		if(BHE==0)
			memory[address[16:1]][7:0]<=cpu_write_data[15:8];
		if(address[0]==0)
			memory[address[16:1]][15:8]<=cpu_write_data[7:0];
	end
end

endmodule