9.10Set IO Address & IRQ in the hardware (mostly for PnP)

After it's set in the hardware don't forget to insure that it also gets set in the driver by using setserial . For non-PnP serial ports they are either set in hardware by jumpers or by running a DOS program ("jumperless") to set them (it may disable PnP). The rest of this subsection is only for PnP serial ports. Here's a list of the possible methods of configuring PnP serial ports:

• Using a PnP BIOS CMOS setup menu (usually only for external devices on ttyS0 (Com1) and ttyS1 (Com2))
• Letting a PnP BIOS automatically configure a PnP serial port See Using a PnP BIOS to IO-IRQ Configure
• Doing nothing if the serial driver recognized your card OK
• Using isapnp for a PnP serial port (non-PCI)
• Using setpci (pciutils or pcitools) for the PCI bus

The IO address and IRQ must be set (by PnP) in their registers each time the system is powered on since PnP hardware doesn't remember how it was set when the power is shut off. A simple way to do this is to let a PnP BIOS know that you don't have a PnP OS and the BIOS will automatically do this each time you start. This might cause problems in Windows (which is a PnP OS) if you start Windows with the BIOS thinking that Windows is not a PnP OS. See Plug-and-Play-HOWTO.

Plug-and-Play (PnP) was designed to automate this io-irq configuring, but for Linux it initially made life much more complicated. In modern Linux (2.4 kernels --partially in 2.2 kernels), each device driver has to do its own PnP (using supplied software which it may utilize).

There is unfortunately no centralized planning for assigning IO addresses and IRQs as there is in MS Windows. But it usually works out OK in Linux anyway.

Using a PnP BIOS to IO-IRQ Configure

While the explanation of how to use setpci or isapnp for io-irq configuring should come with such software, this is not the case if you want to let a PnP BIOS do such configuring. Not all PnP BIOS can do this. The BIOS usually has a CMOS menu for setting up the first two serial ports. This menu may be hard to find. For an "Award" BIOS it was found under "chipset features setup" There is often little to choose from. For ISA serial ports, the first two ports normally get set at the standard IO addresses and IRQs. See More on Serial Port Names

Whether you like it or not, when you start up a PC, a PnP BIOS starts to do PnP (io-irq) configuring of hardware devices. It may do the job partially and turn the rest over to a PnP OS (which Linux is in some sense) or if thinks you don't have a PnP OS it may fully configure all the PnP devices but not configure the device drivers.

If you tell the BIOS that you don't have a PnP OS, then the PnP BIOS should do the configuring of all PnP serial ports --not just the first two. An indirect way to control what the BIOS does (if you have Windows 9x on the same PC) is to "force" a configuration under Windows. See Plug-and-Play-HOWTO and search for "forced". It's easier to use the CMOS BIOS menu which may override what you "forced" under Windows. There could be a BIOS option that can set or disable this "override" capability.

If you add a new PnP device, the BIOS should PnP configure it. It could even change the io-irq of existing devices if required to avoid any conflicts. For this purpose, it keeps a list of non-PnP devices provided that you have told the BIOS how these non-PnP devices are io-irq configured. One way to tell the BIOS this is by running a program called ICU under DOS/Windows.

But how do you find out what the BIOS has done so that you set up the device drivers with this info? The BIOS itself may provide some info, either in its setup menus of via messages on the screen when you turn on your computer. See

* License

* Linux Serial How-To Index