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70 lines
2.2 KiB
Verilog
70 lines
2.2 KiB
Verilog
/*============================================================================
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Game Boy Midi Core - Envelope module
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Aruthor: ModalModule - https://github.com/modalmodule/
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Version: 0.1
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Date: 2024-02-19
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This program is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your option)
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any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along
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with this program. If not, see <http://www.gnu.org/licenses/>.
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===========================================================================*/
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module envelope
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(
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input clk,
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input en,
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input [3:0] decay,
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input note_on,
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input note_repeat,
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input [6:0] note_start,
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input [6:0] vel_start,
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output [6:0] adjusted_vel
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);
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reg [25:0] timer = 'b1;
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reg started;
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reg note_repeat_reg;
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reg [6:0] note_reg;
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reg [6:0] adjusted_vel_reg;
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assign adjusted_vel = adjusted_vel_reg;
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always @ (posedge clk) begin
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if (en && decay < 'd4) begin
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if ((note_reg != note_start || note_repeat_reg) && note_on && !started) begin
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started <= 1;
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adjusted_vel_reg <= vel_start;
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timer <= 'b1;
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note_reg <= note_start;
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note_repeat_reg <= 0;
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end
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if (started) begin
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if (adjusted_vel_reg > 1) begin
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timer <= timer + (26'b1<<decay);
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if (timer > 26'd33554431) begin
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adjusted_vel_reg <= adjusted_vel_reg - 'b1;
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timer <= 'b1;
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end
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end
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if (note_reg != note_start || note_repeat) begin
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started <= 0;
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note_repeat_reg <= note_repeat;
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end
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end
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if (!note_on) begin
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started <= 0;
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if (note_reg == note_start) note_repeat_reg <= note_repeat;
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note_reg <= 0;
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end
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end
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end
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endmodule |