source: bootcd/isolinux/syslinux-6.03/com32/lib/pci/writex.c

#include "pci/pci.h"

void BWL(pci_write)(TYPE v, pciaddr_t a)
{
    for (;;) {
        switch (__pci_cfg_type) {
        case PCI_CFG_AUTO:
            pci_set_config_type(PCI_CFG_AUTO);
            break;              /* Try again */

        case PCI_CFG_TYPE1:
            {
                uint32_t oldcf8;
                cli();
                oldcf8 = inl(0xcf8);
                outl(a, 0xcf8);
                BWL(out) (v, 0xcfc + (a & 3));
                outl(oldcf8, 0xcf8);
                sti();
            }
            return;

        case PCI_CFG_TYPE2:
            {
                uint8_t oldcf8, oldcfa;

                if (a & (0x10 << 11))
                    return;     /* Devices 16-31 not supported */

                cli();
                oldcf8 = inb(0xcf8);
                oldcfa = inb(0xcfa);
                outb(0xf0 + ((a >> (8 - 1)) & 0x0e), 0xcf8);
                outb(a >> 16, 0xcfa);
                BWL(out) (v, 0xc000 + ((a >> (11 - 8)) & 0xf00) + (a & 0xff));
                outb(oldcf8, 0xcf8);
                outb(oldcfa, 0xcfa);
                sti();
            }
            return;

        case PCI_CFG_BIOS:
            __pci_read_write_bios(BIOSCALL, v, a);
            return;

        default:
            return;
        }
    }
}