/**
 *
 */
package net.ttlhacker.quarterv.sim.cpu;

import net.ttlhacker.libttlsim.model.InputPort;
import net.ttlhacker.libttlsim.model.OutputPort;
import net.ttlhacker.libttlsim.model.Simulation;
import net.ttlhacker.libttlsim.model.chips.Series;
import net.ttlhacker.libttlsim.model.chips.StrobedMultiplexerChip;
import net.ttlhacker.libttlsim.model.chips.TristateBusDriver244;
import net.ttlhacker.libttlsim.model.devices.Buffer;
import net.ttlhacker.libttlsim.model.devices.Constant;
import net.ttlhacker.libttlsim.model.devices.TristateBus;

import static net.ttlhacker.libttlsim.model.OutputPort.concat;
import static net.ttlhacker.libttlsim.model.chips.SimpleCombinatorialChip.*;

/**
 * Extracts the immediate field from an instruction.
 *
 * @author jonathan
 *
 */
public class ImmediateExtractor {

    public final InputPort instructionInput;
    public final OutputPort immediateOutput;

    public ImmediateExtractor(Simulation sim, Series nor260Series, Series standardGateSeries, Series muxSeries, Series busDriverSeries) {
        Buffer insnBuffer = new Buffer(sim, 32);
        OutputPort insn = insnBuffer.output;
        this.instructionInput = insnBuffer.input;

        //This decoder provides the immediate encoding type as a one-hot signal.
        ImmediateTypeDecoder typeDecoder = new ImmediateTypeDecoder(sim, standardGateSeries, nor260Series);
        OutputPort i = typeDecoder.i, s = typeDecoder.s, b = typeDecoder.b, u = typeDecoder.u, j = typeDecoder.j;
        typeDecoder.instructionIn.connectTo(insn);

        //Needed bit combinations from the instruction.
        OutputPort signBit = insn.bit(31);
        OutputPort insn20 = insn.bit(20);
        OutputPort insn7 = insn.bit(7);

        //A zero bit.
        Constant constZero = new Constant(sim, 1, 0);
        OutputPort zeroBit = constZero.output;

        //Compute bits 0 and 11 of the immediate using a '153 mux.
        var muxSelISBJ = OR_2INP_74XX32.create(sim, standardGateSeries, 2);
        muxSelISBJ.inputs[0].connectTo(concat(s, b));
        muxSelISBJ.inputs[1].connectTo(concat(j, j));
        var muxFor0And11 = StrobedMultiplexerChip.MUX_4INP_2WIDE_74XX153.create(sim, muxSeries);
        muxFor0And11.selectInput.connectTo(muxSelISBJ.output);
        muxFor0And11.dataInputs[0].connectTo(concat(insn20, signBit));      //I
        muxFor0And11.dataInputs[1].connectTo(concat(insn7, signBit));       //S
        muxFor0And11.dataInputs[2].connectTo(concat(zeroBit, insn7));       //B
        muxFor0And11.dataInputs[3].connectTo(concat(zeroBit, insn20));      //J
        muxFor0And11.strobe.connectTo(u.signExtend(2));                     //Both bits are 0 for U immediates.
        OutputPort imm0 = muxFor0And11.output.bit(0);
        OutputPort imm11 = muxFor0And11.output.bit(1);

        //Compute bits 1 to 4 of the immediate with a '157 mux.
        var muxSelBits1To4 = OR_2INP_74XX32.create(sim, standardGateSeries, 1);
        muxSelBits1To4.inputs[0].connectTo(i);
        muxSelBits1To4.inputs[0].connectTo(j);
        var muxFor1To4 = StrobedMultiplexerChip.MUX_2INP_4WIDE_74XX157.create(sim, muxSeries);
        muxFor1To4.selectInput.connectTo(muxSelBits1To4.output);
        muxFor1To4.dataInputs[0].connectTo(insn.subset(8, 4)); //S and B: insn[8..11]
        muxFor1To4.dataInputs[1].connectTo(insn.subset(21, 4)); //I and J: insn[21..24]
        muxFor1To4.strobe.connectTo(u); //Bits 1..4 are zero for U immediates.
        OutputPort imm1To4 = muxFor1To4.output;

        //Bits 5 to 10 are zero for U immediates and equal to insn[25..30] otherwise.
        var uInverter = INV_74XX04.create(sim, standardGateSeries, 1);
        uInverter.inputs[0].connectTo(u);
        OutputPort notU = uInverter.output;
        var imm5To10And = AND_2INP_74XX08.create(sim, standardGateSeries, 6);
        imm5To10And.inputs[0].connectTo(notU.signExtend(6));
        imm5To10And.inputs[1].connectTo(insn.subset(25, 6));
        OutputPort imm5To10 = imm5To10And.output;

        //Bits 12 to 19 are equal to the sign bit, except for U/J, where they're equal to insn[12..19].
        var uOrJGate = OR_2INP_74XX32.create(sim, standardGateSeries, 1);
        uOrJGate.inputs[0].connectTo(u);
        uOrJGate.inputs[1].connectTo(j);
        var notUOrJGate = INV_74XX04.create(sim, standardGateSeries, 1);
        notUOrJGate.inputs[0].connectTo(uOrJGate.output);
        TristateBus bit12To19Bus = new TristateBus(sim, 8);
        var bit12To19SignDriver = new TristateBusDriver244(sim, bit12To19Bus, busDriverSeries);
        var bit12To19ImmDriver = new TristateBusDriver244(sim, bit12To19Bus, busDriverSeries);
        bit12To19SignDriver.dataIn.connectTo(signBit.signExtend(8));
        bit12To19SignDriver.nOE.connectTo(uOrJGate.output); //Sign bit for anything but U/J
        bit12To19ImmDriver.dataIn.connectTo(insn.subset(12, 8));
        bit12To19ImmDriver.nOE.connectTo(notUOrJGate.output); //Immediate bits for U/J
        OutputPort imm12To19 = bit12To19Bus.output;

        //Bits 20 to 30 are equal to the sign bit, except for U, where they're equal to insn[20..30].
        TristateBus bit20To30Bus = new TristateBus(sim, 11);
        var bit20To30SignDriver = new TristateBusDriver244(sim, bit20To30Bus, busDriverSeries);
        var bit20To30ImmDriver = new TristateBusDriver244(sim, bit20To30Bus, busDriverSeries);
        bit20To30SignDriver.dataIn.connectTo(signBit.signExtend(11));
        bit20To30SignDriver.nOE.connectTo(u); //Sign bit for anything but U
        bit20To30ImmDriver.dataIn.connectTo(insn.subset(20, 11));
        bit20To30ImmDriver.nOE.connectTo(notU); //Immediate bits for U
        OutputPort imm20To30 = bit20To30Bus.output;

        //Assemble the final immediate value
        this.immediateOutput = concat(imm0, imm1To4, imm5To10, imm11, imm12To19, imm20To30, signBit);
    }

}