rtl8139 driver

    // Warten bis der Reset beendet ist
    while ((read_register_byte(netcard, REG_COMMAND) & REG_COMMAND) ==
        CR_RESET);

    // docu says reading ISR clears the interrupts, writting has no effect:
    write_register_word(netcard, REG_INTERRUPT_STATUS, 0);
    // so this is wrong

    write_register_word(netcard, REG_INTERRUPT_MASK, 0xFFFF);

    // not quite sure, but I would use an uint16_t as we read a word, not a dword
    // from ISR
    uint32_t isr = read_register_word(netcard, REG_INTERRUPT_STATUS);

    // where is DMA (PCI bus mastering) enabled? not visible in driver, quite
    // confusuing for the newbie