// Copyright Jamie Iles, 2017
//
// This file is part of s80x86.
//
// s80x86 is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// s80x86 is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with s80x86.  If not, see <http://www.gnu.org/licenses/>.

// INT3
.at 0xcc;
    b_sel IMMEDIATE, immediate 0xc, alu_op SELB, tmp_wr_en, jmp do_int;

// The same as above, but this time it's a 8 bit interrupt number.
.at 0xcd;
    b_sel IMMEDIATE, alu_op SELB, mar_wr_sel Q, mar_write, jmp intN;
.auto_address;
intN:
    a_sel MAR, b_sel IMMEDIATE, immediate 0xff, alu_op AND, mar_write,
        mar_wr_sel Q;
    a_sel MAR, b_sel IMMEDIATE, immediate 0x4, alu_op MUL, tmp_wr_en,
        jmp do_int;

// INTO: the same as int3, but conditional on OF being set.
.at 0xce;
    alu_op GETFLAGS, mdr_write, jmp into;
.auto_address;
into:
    b_sel IMMEDIATE, immediate 0x10, alu_op SELB, tmp_wr_en,
        jmp_if_taken into_taken, ra_sel SP;
    next_instruction;
into_taken:
    jmp do_int;

// Process an interrupt.
// TEMP: interrupt vector address
//
// This is a reasonably large microprocedure, but a reasonable amount of
// repetition.  Start by storing the flags + CS:IP to the stack, clear TF+IF
// and then load the new CS:IP.  As the vectors are stored in segment 0, this
// requires temporarily setting CS to 0 to read the final vector address.
.at 0x12d;
do_int:
    alu_op GETFLAGS, mdr_write, ra_sel SP, jmp do_int_main;
.auto_address;
do_int_main:
    a_sel RA, b_sel IMMEDIATE, immediate 0x2, alu_op SUB,
        mar_write, mar_wr_sel Q, segment SS, segment_force;
    segment SS, segment_force, mem_write;
    a_sel MAR, b_sel IMMEDIATE, immediate 0x2, alu_op SUB,
        mar_write, mar_wr_sel Q, segment_force, segment CS;
    b_sel SR, alu_op SELB, mdr_write, segment SS, segment_force;
    segment SS, segment_force, mem_write;
    a_sel MAR, b_sel IMMEDIATE, immediate 0x2, alu_op SUB,
        mar_write, mar_wr_sel Q;
    a_sel IP, alu_op SELA, mdr_write, segment SS, segment_force;
    segment SS, segment_force, mem_write;
    a_sel MAR, alu_op SELA, rd_sel_source MICROCODE_RD_SEL,
        rd_sel SP;
    b_sel IMMEDIATE, immediate 0x0, alu_op SETFLAGSB, update_flags IF TF;
    b_sel IMMEDIATE, immediate 0x0, alu_op SELB, segment_force,
        segment CS, segment_wr_en;
    b_sel TEMP, alu_op SELB, mar_wr_sel Q, mar_write, segment CS,
        segment_force;
    segment_force, segment CS, mem_read;
    a_sel MDR, alu_op SELA, load_ip;
    a_sel MAR, b_sel IMMEDIATE, immediate 0x2, alu_op ADD, mar_write,
        mar_wr_sel Q, segment CS, segment_force;
    segment_force, segment CS, mem_read;
    a_sel MDR, alu_op SELA, segment_force, segment CS,
        segment_wr_en, next_instruction;