hp-saturn/hp48_io_ram.v

`include "bus_commands.v"

`ifndef _HP48_IO_RAM
`define _HP48_IO_RAM

/**************************************************************************************************
 *
 * I/O ram 
 * length: 64 nibbles
 *
 *
 */


module hp48_io_ram (
	input				strobe,
	input				reset,
	input		[19:0]	address,
	input		[3:0]	command,
	input		[3:0]	nibble_in,
	output	reg [3:0]	nibble_out,
	output	reg			io_ram_active,
	output	reg			io_ram_error
);

localparam IO_RAM_LEN		= 64;

// localparam BUSCMD_DP_WRITE	= C_BUSCMD_DP_WRITE;
// localparam BUSCMD_CONFIGURE = C_BUSCMD_CONFIGURE;


reg	[0:0]	configured;
reg [19:0]	base_addr;
reg [19:0]	pc_ptr;
reg [19:0]	data_ptr;
reg [3:0]	io_ram [0:IO_RAM_LEN-1];

/*
 *
 *
 */

initial
	begin
`ifdef SIM
		$display("io_ram: set unconfigured");
`endif
		configured = 0;
`ifdef SIM
		$display("io_ram: reset error flag");
`endif
		io_ram_error = 1'b0;	
`ifdef SIM
		$display("io_ram: setting base address to 0");
`endif
		base_addr = 0;
`ifdef SIM
		$display("io_ram: setting data pointer to 0");
`endif
		data_ptr = 0;
`ifdef SIM
		$display("io_ram: initializing to 0");
`endif
		for (base_addr = 0; base_addr < IO_RAM_LEN; base_addr++)
			begin
`ifdef SIM
				$write(".");
`endif
				io_ram[base_addr] <= 0; 
			end
`ifdef SIM	
		$write("\n");
		$display("io_ram: initialized");
`endif
	end

/*
 *
 *
 */

always @(*)
	begin
		io_ram_active = 0;
		if ((command==`BUSCMD_PC_READ)|(command==`BUSCMD_DP_READ)|
			(command==`BUSCMD_PC_WRITE)|(command==`BUSCMD_PC_WRITE))
			io_ram_active = ((base_addr>=data_ptr)&(data_ptr<base_addr+IO_RAM_LEN))&(configured);
	end

always @(posedge strobe)
    begin
      
    end

endmodule

`endif