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cbd9d1d69b
Matched the file naming scheme and file structure to that of the other repos for cores, so as to fix an issue with scripts that require specific names. https://github.com/MiSTer-devel/Updater_script_MiSTer/issues/59#issuecomment-781639064
86 lines
3.9 KiB
Verilog
86 lines
3.9 KiB
Verilog
/*
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Implementation is done according to specifications that can be found at https://multimedia.cx/mirror/dialogic-adpcm.pdf
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Most important segments, quote:
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The decoder computes the difference between the previous linear output estimate and the anticipated one.
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This difference is added to the previous estimate to produce the linear output estimate. The input ADPCM
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sample is also presented to the step size calculator to compute the step size estimate
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The decoder accepts ADPCM code values, L(n), and step size values. It calculates a reproduced differential
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value, and accumulates an estimated waveform value, X. Here is a pseudocode algorithm:
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d(n) = (ss(n)*B2)+(ss(n)/2*B1)+(ss(n)/4*BO)+(ss(n)/8)
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if (B3 = 1)
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then d(n) = d(n) * (-1)
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X(n) = X(n-1) + d(n)
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ss(n+1) = ss(n) * 1.1M(L(n))
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-> Calculated from a lookup table
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Initial conditions: When the ADPCM algorithm is reset, the step size ss(n) is set to the minimum value (16) and the
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estimated waveform value X is set to zero (half scale)
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*/
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module adpcm_decoder (
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input reset,
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input clock,
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input [3:0] in_pcm,
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output reg signed [11:0] sample
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);
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reg signed [11:0] differential_value;
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reg signed [6:0] index, delta;
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reg [10:0] step, pr_step;
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reg [15:0] pcm;
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wire signed [11:0] estimation = pcm[15] ? sample + differential_value : sample - differential_value;
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always @(posedge clock)
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begin
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if(reset) begin
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delta <= 7'd0; sample <= 12'd0; differential_value <= 12'd0;
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index <= 7'd0; step <= 11'd0; pr_step <= 11'd0; pcm <= 16'd0;
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end
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else begin
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pcm <= {pcm[11:0], in_pcm[3:0]};
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pr_step <= step;
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case (in_pcm[2:0])
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3'b000: delta <= -7'd1; 3'b001: delta <= -7'd1; 3'b010: delta <= -7'd1; 3'b011: delta <= -7'd1;
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3'b100: delta <= 7'd2; 3'b101: delta <= 7'd4; 3'b110: delta <= 7'd6; 3'b111: delta <= 7'd8;
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endcase
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if (index + delta < 0) index <= 0;
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else if (index + delta > 48) index <= 48;
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else index <= index + delta;
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case (index)
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7'd00: step <= 11'd16; 7'd01: step <= 11'd17; 7'd02: step <= 11'd19; 7'd03: step <= 11'd21;
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7'd04: step <= 11'd23; 7'd05: step <= 11'd25; 7'd06: step <= 11'd28; 7'd07: step <= 11'd31;
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7'd08: step <= 11'd34; 7'd09: step <= 11'd37; 7'd10: step <= 11'd41; 7'd11: step <= 11'd45;
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7'd12: step <= 11'd50; 7'd13: step <= 11'd55; 7'd14: step <= 11'd60; 7'd15: step <= 11'd66;
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7'd16: step <= 11'd73; 7'd17: step <= 11'd80; 7'd18: step <= 11'd88; 7'd19: step <= 11'd97;
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7'd20: step <= 11'd107; 7'd21: step <= 11'd118; 7'd22: step <= 11'd130; 7'd23: step <= 11'd143;
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7'd24: step <= 11'd157; 7'd25: step <= 11'd173; 7'd26: step <= 11'd190; 7'd27: step <= 11'd209;
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7'd28: step <= 11'd230; 7'd29: step <= 11'd253; 7'd30: step <= 11'd279; 7'd31: step <= 11'd307;
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7'd32: step <= 11'd337; 7'd33: step <= 11'd371; 7'd34: step <= 11'd408; 7'd35: step <= 11'd449;
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7'd36: step <= 11'd494; 7'd37: step <= 11'd544; 7'd38: step <= 11'd598; 7'd39: step <= 11'd658;
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7'd40: step <= 11'd724; 7'd41: step <= 11'd796; 7'd42: step <= 11'd876; 7'd43: step <= 11'd963;
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7'd44: step <= 11'd1060; 7'd45: step <= 11'd1166; 7'd46: step <= 11'd1282; 7'd47: step <= 11'd1411;
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7'd48: step <= 11'd1552;
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default: step <= 11'd1552;
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endcase
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differential_value <= {pcm[10] ? pr_step : 12'd0} + {pcm[9] ? (pr_step>>1) : 12'd0} + {pcm[8] ? (pr_step>>2) : 12'd0} + (pr_step>>3);
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if ($signed(estimation) > $signed(2047)) sample <= 12'd2047;
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else if ($signed(estimation) < $signed(-2048)) sample <= -12'd2048;
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else sample <= estimation;
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end
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end
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endmodule
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