57 lines
1.4 KiB
Coq
57 lines
1.4 KiB
Coq
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//KT8 instruction decoder
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//Lots of random logic to do the correct thing for each instruction
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module decode(instruction_i,
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r_value_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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b_value_o,
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b_current_i,
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load_a_o,
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load_b_o,
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load_r_o,
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ram_wr_o,
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ram_data_i );
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input [7:0] instruction_i, r_value_i, ram_data_i, b_current_i;
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output [7:0] b_value_o;
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output [3:0] jump_distance_o;
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output jump_up_o, jump_down_o;
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output load_a_o, load_b_o, load_r_o;
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output ram_wr_o;
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reg jump_up_o, jump_down_o;
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reg [3:0] jump_distance_o;
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//program counter control
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always @(*)
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if instruction_i[7:4] == b'1100 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] == b'1101 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 == h'E0) && (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 == h'E1) && (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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