// taken from the Apple II project by Alex Freed
// and modified for own use

module ramcard(mclk28,reset_in,addr,ram_addr, we, card_ram_we,card_ram_rd, bank1);
  input mclk28;
  input reset_in;
  input [15:0] addr;
  output [17:0] ram_addr;
  input we;
  output card_ram_we;
  output card_ram_rd;
  output bank1;
  
  reg bank1, read_en, write_en, pre_wr_en, bankB, sat_read_en, sat_write_en, sat_pre_wr_en, sat_en;
  reg [2:0] bank16k;
  reg [15:0] addr2;
  wire Dxxx,DEF;
  
  always @(posedge mclk28) begin
    addr2 <= addr;
    if(reset_in) begin
      bank1 <= 0;
      read_en <= 0;
      write_en <= 1;
      pre_wr_en <= 0;
      
      bankB <= 0;
      sat_read_en <= 0;
      sat_write_en <= 0;
      sat_pre_wr_en <= 0;
    end 
    else 
    begin
      if((addr[15:4] == 'hC08) & (addr2 != addr)) begin
        // Looks like a Language Card in slot 0
        bank1 <= addr[3];
        pre_wr_en <= addr[0] & ~we;
        write_en <= addr[0] & pre_wr_en & ~we;
        read_en <= ~(addr[0] ^ addr[1]);
      end
      if((addr[15:4] == 'hC0D) & (addr2 != addr)) begin
        // Looks like Saturn128 Card in slot 5
        if(addr[2] == 0) begin
          // State selection
          bankB <= addr[3];
          sat_pre_wr_en <= addr[0];
          sat_write_en <= addr[0] & sat_pre_wr_en;
          sat_read_en <= ~(addr[0] ^ addr[1]);
        end
        else
        begin
          // 16K bank selection
          bank16k <= {addr[3], addr[1], addr[0]};
        end
      end
    end
  end
  
  assign Dxxx = (addr[15:12] == 4'b1101);
  assign DEF  = ((addr[15:14] == 2'b11) & (addr[13:12] != 2'b00));
  assign ram_addr = ((sat_write_en || sat_read_en) && DEF)?{1'b1, bank16k, addr[13], addr[12] & ~(bankB & Dxxx), addr[11:0]}:{2'b0,addr[15:13], addr[12] & ~(bank1 & Dxxx), addr[11:0]};
  assign card_ram_we = (write_en | sat_write_en);
  assign card_ram_rd = (read_en | sat_read_en);

endmodule