🚀 go-pugleaf

Andy Blair wrote:
> 
> I'm trying to free up IRQs on a Tigereye motherboard, the problem is the
> PIIIX PCI IDE controller.
> 
> If I disable the secondary IDE controller W95 still allocates it IRQ 15.
> 
> If I disable PnP bios support and allocate IRQ15 to an ISA device W95
> disables both primary & secondary IDE controllers.
> 
> Is there any way to disable the secondary IDE without disabling the
> primary ? While still using W95 ;-)
> 
> The problem seems to be with W95 treating the PCI IDE controller as one
> device rather than the primary and secondary controllers individually.
> 
> The idea is to keep using an ATAPI CD when the HDs are SCSI - yes I know
> a SCSI CD would solve the problem but I don't have one and can't see why
> the above should be a problem :-)
> 
> Thanks
> 
> Andy
> --
> Andy Blair     andy@etive.demon.co.uk
Here's some IRQ info that might be helpfull:




              Resolving IRQ and COM Port Conflicts



What are IRQ's and COM Ports?

You can think of the word IRQ as being an abbreviation for Interrupt
Request. An IRQ is a request to the processor to get
the attention needed to interface an device into the system. The system
acknowledges 16 IRQS, numbered 0 through 15. To
use certain devices, the system requires an open IRQ. If two devices try
to use the same IRQ, the system or one of the
devices will likely freeze. 

COM Ports (short for Communication Ports) are modular (serial) channels
to the system, requiring the use of an IRQ. A
COM Port is an extension of an IRQ to a device that is not plugged
directly into the bus. Examples of devices that utilize
COM ports are mice, modems, scanners, and serial printers. The system
will acknowldge up to 4 COM Ports: COM1,
COM2, COM3, and COM4. Each COM port, when in use, requires its own IRQ.
You don't need to enable any COM ports
(technically), but typically systems have 2 in use: mouse (usually on
COM1) and modem (Usually on COM2 or COM4).
Serial ports end in either 9-pin or 25-pin connectors which can easily
be interconverted. 



IRQ Settings

Since the number of available IRQs is limited, they become a valuable
resource. Here is a list of the IRQs and their uses. 

IRQ 0 
     System timer interrupt from TIMER-0. No user-definable options.

IRQ 1 
     Keyboard

IRQ 2 
     Cascade for IRQs 8-15. This is like an overlap IRQ for the
higher-numbered IRQs. IRQ 2 is often a link from IRQ 9.
     For example, a SCSI controller set to IRQ9 would cascade to IRQ 2.

IRQ 3 
     Available. This IRQ should be used for COM2/COM4. Typically, modems
work well on IRQ 3. Two devices can
     share the same IRQ if they have different COM ports. For example,
you can have an internal modem set on
     COM2/IRQ 3, and an external radio-modem or scanner on COM4/IRQ 3.
You will not encounter any IRQ conflict
     unless you try to operate both devices simultaneously. For this
reason, do not share the IRQ you use for the mouse,
     since the mouse is used so often.

IRQ 4 
     Available. IRQ 4 usually services COM1/COM3, and provides the
standard serial mouse connection. As stated above,
     it is not a good idea to have the mouse use a shared IRQ.

IRQ 5 
     Available. This this the most common IRQ for a secondary printer
port. This is also the default IRQ for many sound
     cards, including the SoundBlaster series. If a network card needs a
low IRQ, 5 will usually do.

IRQ 6 
     Floppy Drive controller. No user-definable options.

IRQ 7 
     Primary parallel (printer) port. It is not a good idea to set use
IRQ 7 for anything except parallel.

IRQ 8 
     Real Time Clock. No user-definable options.

IRQ 9 
     Available. This IRQ overlaps to 2. IRQ 9 is a good IRQ to use for
SCSI host adapters, network cards, and sound
     cards that can't use IRQ5 for some reason. SCSI cards should use
IRQ 9 or 11.

IRQ 10 
     Available. This is a good IRQ for a network card, since most
devices can't use it. 

IRQ 11 
     Available. This is the 2nd choice IRQ for a SCSI controller.

IRQ 12 
     Available. Similar to 10,11. This is the IRQ used for a Bus Mouse
(which comes in handy).

IRQ 13 
     Math Coprocessor. No user-definable optinos. 
IRQ 14 
     Hard disk controller (IDE). Each IDE channel requires its own IRQ.
You can control 2 IDE devices with 1 IRQ.

IRQ 15 
     Secondary IDE channel. If you disable the secondary channel, this
becomes available.

The trick is to balance your IRQs so that the do not overlap. Prioritize
you devices by how picky they are. For instance, a
COM port will need to use IRQ 3 or 4 (see COM ports below). You can not
put a modem on IRQ 5, since it requires a
COM port; just as your serial mouse does. Devices that do not do well on
high (above 7) IRQs, eg sound cards, should be
filled in next. The last things to worry about are devices that have
their own ROM to store IRQ and base IO addresses, like
network and SCSI cards. Network and SCSI cards will be able to use the
high IRQs with no problem. These defaults usually
work fine: 


Mouse           COM1    IRQ4
Modem           COM2    IRQ3
Sound Card      no COM  IRQ5
Printer         no COM  IRQ7
SCSI Card       no COM  IRQ9
Netwrok Card    no COM  IRQ10
Bus Mouse       no COM  IRQ12
Secondary IDE   no COM  IRQ15
Extra Serial    COM4    IRQ3 (do not use this at the same time as COM2)

This is a very basic list, but it can be helpful. The number of
possibilities is countless, so you will need to piece your own puzzle
together. It is easier than you think after you try it. 

The best advice I can give for avoiding conficts is to disable
everything that you do not use. If you use an internal
modem, disable COM2 on you controller. If you use a bus mouse, disbale
your COM1. If you do not use your 2nd IDE
channel, disable it. If you only use a printer on your parallel port,
use it in Standard mode, rather than Enhanced. Enhanced
Mode will not let you print any faster; it is for parallel devices (ZIP
drives, CD-ROMs, LapLink) that use high bandwith. If you
are careful, you should not need to disable unused ports, but it will
give you more room to maneuver. 



COM Port Settings

COM ports are esy now that you understand IRQs. Here are the possible
configurations for COM Ports: 


COM     Interrupt       Address
---     ---------       -------
COM1    IRQ4            3f8h
COM2    IRQ3            2f8h
COM3    IRQ4            3e8h
COM4    IRQ3            3f8h

Although there are 4 COM ports, there are only 2 IRQs for them. In
essence, you can have 4 serial devices attached, but use
only 2 at a time. And since your mouse is usually in use, it is not a
good idea to use anything that shares an IRQ with the
mouse. That only leaves us with three simple configurations: 


COM1    IRQ4
COM2    IRQ3
COM4    IRQ3

If you need more devices, you can use a Bus Mouse to free up COM1 /
COM3, or buy a Multiport Board which can handle
from 2 to 128 ports. Modems will work fine on any COM port. Internal
modems are usually defaulted to COM4 to avoid a
conflict with the existing controller. This works fine, but you do have
an extra COM port enable that is not in use (probably).
Most software is defaulted to COM2, so what I usually do with internal
modems is to disable the second COM port on the
controller and use the modem at COM2. External modems are set by
configuring your COM port on the controller. Whatever
that is set to, your modem wil use. This is usually defaulted to COM2. 



Parallel Port Settings

Parallel port settings are similar to COM port settings. A PC can use up
to 3 parallel devices. Here are the default settings: 


LPT Port        IRQ     Address
--------        ---     -------
LPT1:            7      278h
LPT2:            5      378h
LPT3:                   3bch

You can share IRQs for parallel ports as well, but once again not
simultaneously. Most computers will only need 1 Parallel
port.