addrmap Peripheral {
    regfile {
        default regwidth = 32;

        reg {
            name = "BitFields";
            field {
                name = "FIRST";
                sw = r;
                hw = w;
            } first [0:0];
            field {
                name = "SECOND";
                sw = rw;
                hw = rw;
                onwrite = wzc;
            } second [1:1];
        } bit_fields @ 0x0;
    } registers @ 0x100;
};