+module CellularRAM(
+ input clk,
+ input [15:0] address,
+ inout [7:0] data,
+ input wr, rd,
+ output wire cr_nADV, cr_nCE, cr_nOE, cr_nWE, cr_CRE, cr_nLB, cr_nUB, cr_CLK,
+ output wire st_nCE, st_nRST,
+ output wire [22:0] cr_A,
+ inout [15:0] cr_DQ);
+
+ parameter ADDR_PROGADDRH = 16'hFF60;
+ parameter ADDR_PROGADDRM = 16'hFF61;
+ parameter ADDR_PROGADDRL = 16'hFF62;
+ parameter ADDR_PROGDATA = 16'hFF63;
+ parameter ADDR_PROGFLASH = 16'hFF65;
+ parameter ADDR_MBC = 16'hFF64;
+
+ reg rdlatch = 0, wrlatch = 0;
+ reg [15:0] addrlatch = 0;
+ reg [7:0] datalatch = 0;
+
+ reg [7:0] progaddrh, progaddrm, progaddrl;
+
+ reg [22:0] progaddr;
+
+ reg [7:0] mbc_emul = 8'b00000101; // High bit is whether we're poking flash
+ // low 7 bits are the MBC that we are emulating
+
+ assign cr_nADV = 0; /* Addresses are always valid! :D */
+ assign cr_nCE = ~(addrlatch != ADDR_PROGFLASH); /* The chip is enabled */
+ assign cr_nLB = 0; /* Lower byte is enabled */
+ assign cr_nUB = 0; /* Upper byte is enabled */
+ assign cr_CRE = 0; /* Data writes, not config */
+ assign cr_CLK = 0; /* Clock? I think not! */
+
+ assign st_nRST = 1; /* Keep the strataflash out of reset. */
+ assign st_nCE = ~(addrlatch == ADDR_PROGFLASH);
+
+ wire decode = (addrlatch[15:14] == 2'b00) /* extrom */ || (addrlatch[15:13] == 3'b101) /* extram */ || (addrlatch == ADDR_PROGDATA) || (addrlatch == ADDR_PROGFLASH);
+
+ reg [3:0] rambank = 0;
+ reg [8:0] rombank = 1;
+
+ assign cr_nOE = decode ? ~rdlatch : 1;
+ assign cr_nWE = (decode && ((addrlatch == ADDR_PROGDATA) || (addrlatch == ADDR_PROGFLASH) || (mbc_emul[6:0] == 0) || (addrlatch[15:13] == 3'b101))) ? ~wrlatch : 1;
+
+ assign cr_DQ = (~cr_nOE) ? 16'bzzzzzzzzzzzzzzzz : {8'b0, datalatch};
+ assign cr_A = (addrlatch[15:14] == 2'b00) ? /* extrom, home bank */ {9'b0,addrlatch[13:0]} :
+ (addrlatch[15:14] == 2'b01) ? /* extrom, paged bank */ {rombank, addrlatch[13:0]} :
+ (addrlatch[15:13] == 3'b101) ? /* extram */ {1'b1, 5'b0, rambank, addrlatch[12:0]} :
+ ((addrlatch == ADDR_PROGDATA) || (addrlatch == ADDR_PROGFLASH)) ? progaddr :
+ 23'b0;
+
+ always @(posedge clk) begin
+ case (address)
+ ADDR_PROGADDRH: if (wr) progaddrh <= data;
+ ADDR_PROGADDRM: if (wr) progaddrm <= data;
+ ADDR_PROGADDRL: if (wr) progaddrl <= data;
+ ADDR_PROGDATA: if (rd || wr) begin
+ progaddr <= {progaddrh[6:0], progaddrm[7:0], progaddrl[7:0]};
+ {progaddrh[6:0], progaddrm[7:0], progaddrl[7:0]} <= {progaddrh[6:0], progaddrm[7:0], progaddrl[7:0]} + 23'b1;
+ end
+ ADDR_MBC: begin
+ mbc_emul <= data;
+ rambank <= 0;
+ rombank <= 1;
+ end
+ endcase
+
+ if (mbc_emul[6:0] == 5) begin
+ if ((address[15:12] == 4'h2) && wr)
+ rombank <= {rombank[8], data};
+ else if ((address[15:12] == 4'h3) && wr)
+ rombank <= {data[0], rombank[7:0]};
+ else if ((address[15:12] == 4'h4) && wr)
+ rambank <= data[3:0];
+ end
+
+ rdlatch <= rd;
+ wrlatch <= wr;
+ addrlatch <= address;
+ datalatch <= data;
+ end
+
+ assign data = (rdlatch && decode) ?
+ (addrlatch == ADDR_PROGADDRH) ? progaddrh :
+ (addrlatch == ADDR_PROGADDRM) ? progaddrm :
+ (addrlatch == ADDR_PROGADDRL) ? progaddrl :
+ cr_DQ
+ : 8'bzzzzzzzz;
+endmodule
+