69 lines
1.7 KiB
Coq
69 lines
1.7 KiB
Coq
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//KT8 instruction logic
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//handles control of program counter based on instructions
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module program_control(instruction_i,
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r_value_i,
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rst_i,
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jump_up_o,
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jump_down_o,
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jump_distance_o,
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rst_o,
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hlt_o);
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input [7:0] instruction_i;
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input [7:0] r_value_i;
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input rst_i;
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output reg [3:0] jump_distance_o;
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output reg jump_up_o, jump_down_o, rst_o, hlt_o;
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//special block for reset and halt opcode. Immediately triggers reset
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always @(*) begin
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if (rst_i) begin
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hlt_o = 0;
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rst_o = 0;
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end else if (instruction_i == 8'hF0) begin
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#1 rst_o = 1;
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hlt_o = 0;
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end else if (instruction_i == 8'hF1) begin
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hlt_o = 1;
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rst_o = 0;
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end else begin
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#1 rst_o = 0;
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hlt_o = 0;
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end
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end
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//program counter control
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always @(*) begin
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if (instruction_i[7:4] == 4'b1100) begin
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//FJMP
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jump_up_o = 1;
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jump_down_o = 0;
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jump_distance_o = instruction_i[3:0];
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end else if (instruction_i[7:4] == 4'b1101) begin
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//BJMP
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jump_up_o = 0;
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jump_down_o = 1;
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jump_distance_o = instruction_i[3:0];
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end else if ((instruction_i == 8'hE0) && (r_value_i == 0)) begin
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//SKIPZ and R==0, so skip
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jump_up_o = 1;
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jump_down_o = 0;
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jump_distance_o = 2;
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end else if ((instruction_i == 8'hE1) && (r_value_i != 0)) begin
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//SKIPNZ and R!=0, so skip
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jump_up_o = 1;
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jump_down_o = 0;
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jump_distance_o = 2;
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end else begin
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//normal count up
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jump_up_o = 0;
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jump_down_o = 0;
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jump_distance_o = 0;
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end
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end
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endmodule
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