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/trunk/rtl/verilog/vector2scanline.v
13,81 → 13,98
//
// Dependencies:
//
// Revision:
// Revision 0.01 - File Created
// Additional Comments:
//
//////////////////////////////////////////////////////////////////////////////////
 
module vector2scanline(
input clk,
input clk, // clock
 
input strobe,
input [9:0] x,
input [9:0] y,
input strobe, // new exposed pixel trigger
input [9:0] x, // column of exposed pixel
input [9:0] y, // row of exposed pixel
 
input [9:0] xout,
input [9:0] yout,
input newline,
input newframe,
output [7:0] pixel
);
// Video output interface
input [9:0] xout, // current pixel column
input [9:0] yout, // current pixel row
input newline, // line buffer swap signal
input newframe, // new frame signal
output [7:0] pixel // output pixel intensity
);
 
parameter X_WIDTH = 10;
parameter Y_WIDTH = 10;
parameter HIST_WIDTH = 10;
parameter AGE_WIDTH = 8;
// TODO: figure out how to apply parameters to the port sizes above
parameter X_WIDTH = 10; // bit width of column coordinate
parameter Y_WIDTH = 10; // bit width of row coordinate
parameter HIST_WIDTH = 10; // log2 of maximum lit pixels (exposure buffer)
parameter AGE_WIDTH = 8; // width of exposure age counter
 
reg [X_WIDTH+Y_WIDTH+AGE_WIDTH-1:0] exposures [(2**HIST_WIDTH)-1:0];
reg [X_WIDTH+Y_WIDTH+AGE_WIDTH-1:0] expr;
wire [X_WIDTH-1:0] expx;
wire [Y_WIDTH-1:0] expy;
wire [7:0] expi;
wire exposed;
reg [HIST_WIDTH-1:0] exprptr=0, expwptr=0;
// double-buffered; one gets wiped as it is displayed
// the other gets filled in with current exposures
reg [AGE_WIDTH-1:0] scanline0 [(2**X_WIDTH)-1:0];
reg [AGE_WIDTH-1:0] scanline1 [(2**X_WIDTH)-1:0];
reg [AGE_WIDTH-1:0] pixelout;
reg bufsel = 0;
wire [X_WIDTH-1:0] sl0w, sl1w;
// positions and age of lit pixels
reg [X_WIDTH+Y_WIDTH+AGE_WIDTH-1:0] exposures [(2**HIST_WIDTH)-1:0];
// output register of exposed pixels buffer
reg [X_WIDTH+Y_WIDTH+AGE_WIDTH-1:0] expr;
// data for next pixel to store in exposure buffer
wire [X_WIDTH-1:0] expx;
wire [Y_WIDTH-1:0] expy;
wire [7:0] expi;
// whether this pixel needs to be stored back in exposure buffer
wire exposed;
// addresses for exposure buffer read and write ports
reg [HIST_WIDTH-1:0] exprptr=0, expwptr=0;
 
always @(posedge clk) begin
expr<=exposures[exprptr];
if (!strobe) begin
exprptr<=exprptr+1;
end
end
assign expx = strobe?x:expr[X_WIDTH+Y_WIDTH+AGE_WIDTH-1:Y_WIDTH+AGE_WIDTH];
assign expy = strobe?y:expr[Y_WIDTH+AGE_WIDTH-1:AGE_WIDTH];
assign expi = strobe?(2**AGE_WIDTH)-1:expr[AGE_WIDTH-1:0];
assign exposed = expi!=0;
// scanline pixel buffers, store intensity
// double-buffered; one gets wiped as it is displayed
// the other gets filled in with current exposures
reg [AGE_WIDTH-1:0] scanline0 [(2**X_WIDTH)-1:0];
reg [AGE_WIDTH-1:0] scanline1 [(2**X_WIDTH)-1:0];
// output intensity for current pixel
reg [AGE_WIDTH-1:0] pixelout;
// selection register for which scanline buffer is output/filled in
reg bufsel = 0;
// address lines for scanline buffers
wire [X_WIDTH-1:0] sl0w, sl1w;
 
always @(posedge clk) begin
// Feed incoming exposures into exposure buffer
if (exposed) begin
exposures[expwptr] <= {expx, expy, expy==yout?expi-1:expi};
expwptr <= expwptr+1;
end
end
// RAM read out of exposure buffer
always @(posedge clk) begin
expr<=exposures[exprptr];
if (!strobe) begin
// do not skip current read position if strobe inserts a new pixel
exprptr<=exprptr+1;
end
end
 
assign sl0w=bufsel?expx:xout;
assign sl1w=bufsel?xout:expx;
always @(posedge clk) begin
// Read out & wipe front buffer
// Store exposures for current scanline as well
if (expy==(y+1)) begin
scanline0[sl0w] <= bufsel?expi:0;
scanline1[sl1w] <= bufsel?0:expi;
pixelout <= bufsel?scanline1[xout]:scanline0[xout];
end
if (newframe) begin
bufsel <= ~bufsel;
end
end
// decode and mux: split fields from exposure buffer, or collect new at strobe
assign expx = strobe?x:expr[X_WIDTH+Y_WIDTH+AGE_WIDTH-1:Y_WIDTH+AGE_WIDTH];
assign expy = strobe?y:expr[Y_WIDTH+AGE_WIDTH-1:AGE_WIDTH];
assign expi = strobe?(2**AGE_WIDTH)-1:expr[AGE_WIDTH-1:0];
// detect whether pixel even needs to be stored back
assign exposed = expi!=0;
always @(posedge clk) begin
// Feed incoming exposures into exposure buffer
if (exposed) begin
exposures[expwptr] <= {expx, expy, expy==yout?expi-1:expi};
expwptr <= expwptr+1;
end
end
 
assign pixel = pixelout;
// scanline buffers switch output or expose roles based on bufsel
assign sl0w=bufsel?expx:xout;
assign sl1w=bufsel?xout:expx;
always @(posedge clk) begin
// Read out front buffer
pixelout <= bufsel?scanline1[sl1w]:scanline0[sl0w];
// TODO: use a next line input port, this incrementer won't work for
// line 0 (which is unused in display.vhd) and could be shared.
if (expy==(y+1)) begin
// Store exposures for current scanline and wipe front buffer
scanline0[sl0w] <= bufsel?expi:0;
scanline1[sl1w] <= bufsel?0:expi;
end
// swap buffers when signaled
if (newline) begin
bufsel <= ~bufsel;
end
end
 
// output pixel intensity
assign pixel = pixelout;
endmodule

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