sheila.js

// sheila emulation routines for ElkJs
// written by Darren Coles

ElkJs.Sheila = function () {
    var self = {};

    var interrupt_status = new Object();

    interrupt_status.nmi = false;
    interrupt_status.high_tone = false;
    interrupt_status.rtc = false;
    interrupt_status.display_end = false;
    interrupt_status.power_on = true;

    var interrupt_enable = new Object();
    interrupt_enable.massterIRQ = false;
    interrupt_enable.reset = false;
    interrupt_enable.display_end = false;
    interrupt_enable.rtc = false;
    interrupt_enable.transmit = false;
    interrupt_enable.receive = false;
    interrupt_enable.high_tone = false;

    self.interrupt = false;

    var paletteRegs = new Uint8Array([0, 0, 0, 0, 0, 0, 0, 0]);

    self.soundFreq = 0;
    self.soundMode = 0;

    self.romBank = 0;
    //self.intRomBank = 0;
    //self.extRom = 0;	
    self.screenMode = 0;

    var screenaddrLo = 0;
    var screenaddrHi = 0;

    var tapeData = 0;

    var fe05 = 0;
    var fe06 = 0;
    var fe07 = 0;

    self.caps = false;
    self.tapeMotor = false;

    self.palette = new Uint8Array(16);
    for (var i = 0; i < 16; i++) self.palette[i] = 0;

    self.casetteDataRead = false;

    //FEx0 - interrupt status and control (R/W)
    //	7 - not used
    //	6 - high tone detect
    //	5 - transmit data empty
    //	4 - receive data full
    //	3 - realtime clock
    //	2 - display end interrupt
    //	1 - power on reset
    //	0 - master IRQ
    //FEx2/3 - screen start (W)
    //FEx4 - cassette data shift register (R/W)
    //FEx5 - interrupt clear and paging (W)
    //	7 - NMI
    //	6 - High tone
    //	5 - RTC
    //	4 - frame end
    //	3 - rom page enable
    //	2/1/0 - rom paging
    //FEx6 - the counter (W)
    //	sound and casette data timing
    //FEx7 - misc control (W)
    //	7 - caps lock
    //	6 - casette motor
    //	5/4/3 - screen mode
    //	2/1/0 - 00 - casette input, 01 - sound generation, 10 - casette output, 11 - unused
    //FEx8 - FExF - palette (W)

    function updatePalette(cols, reg0, reg1) {
        if (cols[0] != -1) {
            self.palette[cols[0]] |= 4;
            self.palette[cols[0]] ^= ((paletteRegs[reg0] & 16) ? 4 : 0);
        }
        if (cols[1] != -1) {
            self.palette[cols[1]] |= 4;
            self.palette[cols[1]] ^= ((paletteRegs[reg0] & 32) ? 4 : 0);
        }
        if (cols[2] != -1) {
            self.palette[cols[2]] |= 6;
            self.palette[cols[2]] ^= ((paletteRegs[reg0] & 4) ? 2 : 0) | ((paletteRegs[reg0] & 64) ? 4 : 0);
        }
        if (cols[3] != -1) {
            self.palette[cols[3]] |= 6;
            self.palette[cols[3]] ^= ((paletteRegs[reg0] & 8) ? 2 : 0) | ((paletteRegs[reg0] & 128) ? 4 : 0);
        }

        if (cols[0] != -1) {
            self.palette[cols[0]] |= 3;
            self.palette[cols[0]] ^= ((paletteRegs[reg1] & 1) ? 1 : 0) | ((paletteRegs[reg1] & 16) ? 2 : 0);
        }
        if (cols[1] != -1) {
            self.palette[cols[1]] |= 3;
            self.palette[cols[1]] ^= ((paletteRegs[reg1] & 2) ? 1 : 0) | ((paletteRegs[reg1] & 32) ? 2 : 0);
        }
        if (cols[2] != -1) {
            self.palette[cols[2]] |= 1;
            self.palette[cols[2]] ^= ((paletteRegs[reg1] & 4) ? 1 : 0);
        }
        if (cols[3] != -1) {
            self.palette[cols[3]] |= 1;
            self.palette[cols[3]] ^= ((paletteRegs[reg1] & 8) ? 1 : 0);
        }
    }

    function recalcPalette() {
        var cols = new Uint8Array(4);
        switch (self.screenMode) {
            case 0:
            case 3:
            case 4:
            case 6:
            case 7:
                cols[0] = 0;
                cols[1] = -1;
                cols[2] = 1;
                cols[3] = -1;
                updatePalette(cols, 0, 1);
                break;

            case 1:
            case 5:
                cols[0] = 0;
                cols[1] = 1;
                cols[2] = 2;
                cols[3] = 3;
                updatePalette(cols, 0, 1);
                break;

            case 2:
                cols[0] = 0;
                cols[1] = 2;
                cols[2] = 8;
                cols[3] = 10;
                updatePalette(cols, 0, 1);

                cols[0] = 4;
                cols[1] = 6;
                cols[2] = 12;
                cols[3] = 14;
                updatePalette(cols, 2, 3);

                cols[0] = 5;
                cols[1] = 7;
                cols[2] = 13;
                cols[3] = 15;
                updatePalette(cols, 4, 5);

                cols[0] = 1;
                cols[1] = 3;
                cols[2] = 9;
                cols[3] = 11;
                updatePalette(cols, 6, 7);

                break;

        }

    }

    function check_interrupts() {
        self.interrupt = ((interrupt_enable.display_end & interrupt_status.display_end) | (interrupt_enable.rtc & interrupt_status.rtc) | (interrupt_enable.high_tone & interrupt_status.high_tone) |
		(interrupt_enable.receive & interrupt_status.receive) | interrupt_enable.transmit & interrupt_status.transmit);
    }

    self.trigger_vbl = function () {
        interrupt_status.display_end = true;
        check_interrupts();
    }

    self.trigger_rtc = function () {
        interrupt_status.rtc = true;
        check_interrupts();
    }

    self.trigger_hightone = function () {
        interrupt_status.high_tone = true;
        check_interrupts();
    }

    self.trigger_receive = function () {
        interrupt_status.receive = true;
        check_interrupts();
    }

    self.clear_receive = function () {
        interrupt_status.receive = false;
        check_interrupts();
    }

    self.reset = function () {
        interrupt_enable.massterIRQ = false;
        interrupt_enable.reset = false;
        interrupt_enable.display_end = false;
        interrupt_enable.rtc = false;
        interrupt_enable.transmit = false;
        interrupt_enable.receive = false;
        interrupt_enable.high_tone = false;

        interrupt_status.nmi = false;
        interrupt_status.high_tone = false;
        interrupt_status.rtc = false;
        interrupt_status.display_end = false;
        interrupt_status.receive = false;
        interrupt_status.transmit = false;

        interrupt_status.power_on = true;

        self.caps = false;
        self.tapeMotor = false;

    }

    self.write = function (addr, val) {

        addr = addr & 0xf;

        if (addr == 0) {
            interrupt_enable.massterIRQ = (val & 0x1) != 0;
            interrupt_enable.reset = (val & 0x2) != 0;
            interrupt_enable.display_end = (val & 0x4) != 0;
            interrupt_enable.rtc = (val & 0x8) != 0;
            interrupt_enable.receive = (val & 0x10) != 0;
            interrupt_enable.transmit = (val & 0x20) != 0;
            interrupt_enable.high_tone = (val & 0x40) != 0;
            check_interrupts();
        }

        if (addr == 2) {
            //FEx2 (screen start low)
            screenaddrLo = val;
        }
        else if (addr == 3) {
            //FEx3 (screen start high)
            screenaddrHi = val;
        }
        else if (addr == 4) {
            tapeData = val;
            interrupt_status.transmit = false;
        }
        else if (addr == 5) {
            fe05 = val;
            if ((val & 0xf) >= 8) self.romBank = val & 0xF;
            else if (self.romBank >= 0xC | self.romBank < 8) {
                self.romBank = val & 0xF;
            }
            if (val & 0x10) interrupt_status.display_end = false;
            if (val & 0x20) interrupt_status.rtc = false;
            if (val & 0x40) interrupt_status.high_tone = false;
            check_interrupts();
        }
        else if (addr == 6) {
            fe06 = val;
            //if (self.soundMode==1) {
            self.soundFreq = 1000000 / (16 * (val + 1));
            //}
        }
        else if (addr == 7) {
            //FEx7 (misc control)
            fe07 = val;
            self.caps = (val & 0x80) != 0;

            self.tapeMotor = (val & 0x40) != 0;
            self.screenMode = (val & 0x38) >> 3;
            recalcPalette();
            self.soundMode = (val & 6) >> 1;
            if (self.soundMode != 1) {
                self.soundFreq = 0;
            }

        }
        else if (addr > 7) {
            paletteRegs[addr - 8] = val;
            recalcPalette();
        }
    }

    self.read = function (addr) {
        addr = addr & 0xf;

        if (addr == 0) {
            var v = 0;

            if (interrupt_status.display_end) v |= 4;
            if (interrupt_status.rtc) v |= 8;
            if (interrupt_status.high_tone) v |= 64;

            if (interrupt_status.receive) v |= 16;
            if (interrupt_status.transmit) v |= 32;

            if (v) v |= 1;
            if (interrupt_status.power_on) v |= 2;

            interrupt_status.power_on = false;

            return v | 0x80;


        }
        else if (addr == 4) {
            interrupt_status.receive = false;
            self.casetteDataRead = true;
            return tapeData;
        }

        return undefined;
    }

    self.loadSnapshot = function (buffer, offset) {
        //ier
        //isr
        //screen low 0xfe02)
        //screen high (0xfe03)
        //casette (0xfe04)
        //rom page - 0xfe05
        //current rom
        //fe06,fe07,fe08,fe09,fe0a,fe0b,fe0c,fe0d,fe0e,fe0f
        //4 bytes - number of 16mhz cycles since last display end interrupt

        self.write(0xfe00, buffer[offset + 0]);

        v = buffer[offset + 1];
        interrupt_status.power_on = (v & 2) != 0;
        interrupt_status.display_end = (v & 4) != 0;
        interrupt_status.rtc = (v & 8) != 0;
        interrupt_status.receive = (v & 16) != 0;
        interrupt_status.transmit = (v & 32) != 0;
        interrupt_status.high_tone = (v & 64) != 0;

        self.write(0xfe02, buffer[offset + 2]);
        self.write(0xfe03, buffer[offset + 3]);
        self.write(0xfe04, buffer[offset + 4]);
        self.write(0xfe05, buffer[offset + 5]);
        self.romBank = buffer[offset + 6] & 0xf;
        //self.intRomBank=self.romBank;
        for (var i = 6; i < 16; i++) {
            self.write(0xfe00 + i, buffer[offset + i + 1]);  //fe06,fe07,fe08,fe09,fe0a,fe0b,fe0c,fe0d,fe0e,fe0f
        }


    }

    self.makeSnapshotData = function () {
        var bytes = new Array();
        bytes.push(0); //update byte

        var icr = (interrupt_enable.massterIRQ ? 1 : 0) + (interrupt_enable.reset ? 2 : 0) + (interrupt_enable.display_end ? 4 : 0) + (interrupt_enable.rtc ? 8 : 0) + (interrupt_enable.receive ? 0x10 : 0) + (interrupt_enable.transmit ? 0x20 : 0) + (interrupt_enable.high_tone ? 0x40 : 0);
        bytes.push(icr);

        bytes.push(self.read(0xfe00));

        bytes.push(screenaddrLo);
        bytes.push(screenaddrHi);
        bytes.push(tapeData);
        bytes.push(fe05);
        bytes.push(self.romBank);
        bytes.push(fe06);
        bytes.push(fe07);
        bytes.push(paletteRegs[0]);
        bytes.push(paletteRegs[1]);
        bytes.push(paletteRegs[2]);
        bytes.push(paletteRegs[3]);
        bytes.push(paletteRegs[4]);
        bytes.push(paletteRegs[5]);
        bytes.push(paletteRegs[6]);
        bytes.push(paletteRegs[7]);

        bytes.push(0);bytes.push(0);bytes.push(0);bytes.push(0);
        return bytes;
    }
    self.getScreenAddress = function () {
        return ((screenaddrLo & 224) << 1) + ((screenaddrHi & 63) << 9);
    }

    self.addTapeBit = function (data) {
        if (data) {
            tapeData = (tapeData >> 1) | 0x80;
        }
        else {
            tapeData >= 1;
        }
    }

    self.setTapeData = function (data) {
        tapeData = data;
    }

    return self;
}