input clk,
input wr, rd);
+ reg rdlatch = 0;
reg [7:0] odata;
// synthesis attribute ram_style of rom is block
initial $readmemh("rom.hex", rom);
wire decode = address[15:13] == 0;
- always @(posedge clk)
+ always @(posedge clk) begin
+ rdlatch <= rd && decode;
odata <= rom[address[10:0]];
- assign data = (rd && decode) ? odata : 8'bzzzzzzzz;
+ end
+ assign data = rdlatch ? odata : 8'bzzzzzzzz;
endmodule
module BootstrapROM(
input clk,
input wr, rd);
+ reg rdlatch = 0;
+ reg [7:0] addrlatch = 0;
reg [7:0] brom [255:0];
initial $readmemh("bootstrap.hex", brom);
wire decode = address[15:8] == 0;
- wire [7:0] odata = brom[address[7:0]];
- assign data = (rd && decode) ? odata : 8'bzzzzzzzz;
+ wire [7:0] odata = brom[addrlatch];
+ always @(posedge clk) begin
+ rdlatch <= rd && decode;
+ addrlatch <= address[7:0];
+ end
+ assign data = rdlatch ? odata : 8'bzzzzzzzz;
endmodule
module MiniRAM(
reg [7:0] ram [127:0];
wire decode = (address >= 16'hFF80) && (address <= 16'hFFFE);
+ reg rdlatch = 0;
reg [7:0] odata;
- assign data = (rd && decode) ? odata : 8'bzzzzzzzz;
+ assign data = rdlatch ? odata : 8'bzzzzzzzz;
always @(posedge clk)
begin
- if (decode) // This has to go this way. The only way XST knows how to do
- begin // block ram is chip select, write enable, and always
+ rdlatch <= rd && decode;
+ if (decode) // This has to go this way. The only way XST knows how to do
+ begin // block ram is chip select, write enable, and always
if (wr) // reading. "else if rd" does not cut it ...
ram[address[6:0]] <= data;
odata <= ram[address[6:0]];
parameter ADDR_PROGADDRL = 16'hFF62;
parameter ADDR_PROGDATA = 16'hFF63;
+ reg rdlatch = 0, wrlatch = 0;
+ reg [15:0] addrlatch = 0;
+ reg [7:0] datalatch = 0;
+
reg [7:0] progaddrh, progaddrm, progaddrl;
assign cr_nADV = 0; /* Addresses are always valid! :D */
assign cr_CRE = 0; /* Data writes, not config */
assign cr_CLK = 0; /* Clock? I think not! */
- wire decode = (address[15:14] == 2'b00) /* extrom */ || (address[15:13] == 3'b101) /* extram */ || (address == ADDR_PROGDATA);
+ wire decode = (addrlatch[15:14] == 2'b00) /* extrom */ || (addrlatch[15:13] == 3'b101) /* extram */ || (addrlatch == ADDR_PROGDATA);
- assign cr_nOE = decode ? ~rd : 1;
- assign cr_nWE = decode ? ~wr : 1;
+ assign cr_nOE = decode ? ~rdlatch : 1;
+ assign cr_nWE = decode ? ~wrlatch : 1;
- assign cr_DQ = (~cr_nOE) ? 16'bzzzzzzzzzzzzzzzz : {8'b0, data};
- assign cr_A = (address[15:14] == 2'b00) ? /* extrom */ {9'b0,address[13:0]} :
- (address[15:13] == 3'b101) ? {1'b1, 9'b0, address[12:0]} :
- (address == ADDR_PROGDATA) ? {progaddrh[6:0], progaddrm[7:0], progaddrl[7:0]} :
+ assign cr_DQ = (~cr_nOE) ? 16'bzzzzzzzzzzzzzzzz : {8'b0, datalatch};
+ assign cr_A = (addrlatch[15:14] == 2'b00) ? /* extrom */ {9'b0,addrlatch[13:0]} :
+ (addrlatch[15:13] == 3'b101) ? {1'b1, 9'b0, addrlatch[12:0]} :
+ (addrlatch == ADDR_PROGDATA) ? {progaddrh[6:0], progaddrm[7:0], progaddrl[7:0]} :
23'b0;
reg [7:0] regbuf;
- always @(posedge clk)
+ always @(posedge clk) begin
case (address)
ADDR_PROGADDRH: if (wr) progaddrh <= data;
ADDR_PROGADDRM: if (wr) progaddrm <= data;
ADDR_PROGADDRL: if (wr) progaddrl <= data;
endcase
+ rdlatch <= rd;
+ wrlatch <= wr;
+ addrlatch <= address;
+ datalatch <= data;
+ end
- assign data = (rd && decode) ?
- (address == ADDR_PROGADDRH) ? progaddrh :
- (address == ADDR_PROGADDRM) ? progaddrm :
- (address == ADDR_PROGADDRL) ? progaddrl :
+ assign data = (rdlatch && decode) ?
+ (addrlatch == ADDR_PROGADDRH) ? progaddrh :
+ (addrlatch == ADDR_PROGADDRM) ? progaddrm :
+ (addrlatch == ADDR_PROGADDRL) ? progaddrl :
cr_DQ
: 8'bzzzzzzzz;
endmodule
wire decode = (address >= 16'hC000) && (address <= 16'hFDFF); /* This includes echo RAM. */
reg [7:0] odata;
- assign data = (rd && decode) ? odata : 8'bzzzzzzzz;
+ reg rdlatch = 0;
+ assign data = rdlatch ? odata : 8'bzzzzzzzz;
always @(posedge clk)
begin
+ rdlatch <= rd && decode;
if (decode) // This has to go this way. The only way XST knows how to do
begin // block ram is chip select, write enable, and always
if (wr) // reading. "else if rd" does not cut it ...
wire decode = address == 16'hFF51;
reg [7:0] odata;
- assign data = (rd && decode) ? odata : 8'bzzzzzzzz;
+ reg rdlatch = 0;
+ assign data = rdlatch ? odata : 8'bzzzzzzzz;
always @(posedge clk)
begin
+ rdlatch <= rd && decode;
if (decode && rd)
odata <= switches;
else if (decode && wr)
.data(data[0]),
.clk(clk),
.wr(wr[0]),
- .rd(rd[0])
+ .rd(rd[0]),
.cr_nADV(cr_nADV),
.cr_nCE(cr_nCE),
.cr_nOE(cr_nOE),
- .cr_nWR(cr_nWE),
+ .cr_nWE(cr_nWE),
.cr_CRE(cr_CRE),
.cr_nLB(cr_nLB),
.cr_nUB(cr_nUB),
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