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Line 36... |
input [11:0] y_coord_i;
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input [11:0] y_coord_i;
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output [31:0] address_o;
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output [31:0] address_o;
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output [6:0] mb_o;
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output [6:0] mb_o;
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output [6:0] me_o;
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output [6:0] me_o;
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parameter BPP6 = 3'd0;
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parameter BPP8 = 3'd1;
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parameter BPP8 = 3'd1;
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parameter BPP12 = 3'd2;
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parameter BPP12 = 3'd2;
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parameter BPP16 = 3'd3;
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parameter BPP16 = 3'd3;
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parameter BPP24 = 3'd4;
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parameter BPP24 = 3'd4;
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parameter BPP32 = 3'd5;
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parameter BPP32 = 3'd5;
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// This coefficient is a fixed point fraction representing the inverse of the
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// number of pixels per strip. The inverse (reciprocal) is used for a high
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// speed divide operation.
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reg [15:0] coeff;
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reg [15:0] coeff;
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always @(color_depth_i)
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always @(color_depth_i)
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case(color_depth_i)
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case(color_depth_i)
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BPP6: coeff = 3121; // 1/21 * 65536
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BPP8: coeff = 4096; // 1/16 * 65536
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BPP8: coeff = 4096; // 1/16 * 65536
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BPP12: coeff = 6554; // 1/10 * 65536
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BPP12: coeff = 6554; // 1/10 * 65536
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BPP16: coeff = 8192; // 1/8 * 65536
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BPP16: coeff = 8192; // 1/8 * 65536
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BPP24: coeff = 13107; // 1/5 * 65536
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BPP24: coeff = 13107; // 1/5 * 65536
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BPP32: coeff = 16384; // 1/4 * 65536
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BPP32: coeff = 16384; // 1/4 * 65536
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endcase
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endcase
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// Bits per pixel minus one.
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reg [5:0] bpp;
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reg [5:0] bpp;
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always @(color_depth_i)
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always @(color_depth_i)
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case(color_depth_i)
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case(color_depth_i)
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BPP6: bpp = 5;
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BPP8: bpp = 7;
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BPP8: bpp = 7;
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BPP12: bpp = 11;
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BPP12: bpp = 11;
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BPP16: bpp = 15;
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BPP16: bpp = 15;
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BPP24: bpp = 23;
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BPP24: bpp = 23;
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BPP32: bpp = 31;
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BPP32: bpp = 31;
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endcase
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endcase
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// This coefficient is the number of bits used by all pixels in the strip.
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// Used to determine pixel placement in the strip.
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reg [7:0] coeff2;
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reg [7:0] coeff2;
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always @(color_depth_i)
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always @(color_depth_i)
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case(color_depth_i)
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case(color_depth_i)
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BPP6: coeff2 = 126;
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BPP8: coeff2 = 128;
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BPP8: coeff2 = 128;
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BPP12: coeff2 = 120;
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BPP12: coeff2 = 120;
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BPP16: coeff2 = 128;
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BPP16: coeff2 = 128;
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BPP24: coeff2 = 120;
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BPP24: coeff2 = 120;
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BPP32: coeff2 = 128;
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BPP32: coeff2 = 128;
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endcase
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endcase
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// Compute the fixed point horizonal strip number value. This has 16 binary
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// point places.
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wire [27:0] strip_num65k = x_coord_i * coeff;
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wire [27:0] strip_num65k = x_coord_i * coeff;
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wire [15:0] strip_fract = strip_num65k[15:0]+16'h7F;
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// Truncate off the binary fraction to get the strip number. The strip
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// number will be used to form part of the address.
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wire [13:0] strip_num = strip_num65k[27:16];
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// Calculate pixel position within strip using the fractional part of the
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// horizontal strip number.
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wire [15:0] strip_fract = strip_num65k[15:0]+16'h7F; // +7F to round
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// Pixel beginning bit is ratio of pixel # into all bits used by pixels
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wire [15:0] ndx = strip_fract[15:7] * coeff2;
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wire [15:0] ndx = strip_fract[15:7] * coeff2;
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assign mb_o = ndx[15:9];
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assign mb_o = ndx[15:9]; // Get whole pixel position (discard fraction)
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assign me_o = mb_o + bpp;
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assign me_o = mb_o + bpp; // Set high order position for mask
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// num_strips is essentially a constant value unless the screen resolution changes.
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// num_strips is essentially a constant value unless the screen resolution changes.
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// Gain performance here by regstering the multiply so that there aren't two
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// Gain performance here by regstering the multiply so that there aren't two
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// cascaded multiplies when calculating the offset.
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// cascaded multiplies when calculating the offset.
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reg [27:0] num_strips65k;
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reg [27:0] num_strips65k;
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always @(posedge clk)
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always @(posedge clk)
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num_strips65k <= hdisplayed_i * coeff;
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num_strips65k <= hdisplayed_i * coeff;
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wire [13:0] strip_num = strip_num65k[27:16];
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wire [13:0] num_strips = num_strips65k[27:16];
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wire [13:0] num_strips = num_strips65k[27:16];
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wire [31:0] offset = {{4'b0,num_strips} * y_coord_i + strip_num,4'h0};
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wire [31:0] offset = {{4'b0,num_strips} * y_coord_i + strip_num,4'h0};
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assign address_o = base_address_i + offset;
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assign address_o = base_address_i + offset;
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