Introduction

Using Interrupt Mode, IRQ resource limitations must be considered.

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Finding an exclusive IRQ often requires physically moving hardware around in the system or disabling other Windows devices.

This Application Note explainesexplains, how the Interrupt Number is assigned by the System and how to search for a free interrupt number in case of shared IRQ.

Physical Interrupt Number

With PCI / PCIE hardware, interrupt numbers are distributed to the hardware either by the BIOS or the operating system.

By default, our PCI / PCIE PCIe cards always request an interrupt and therefore should get one assigned.

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By changing the view in the device manager to "ressources resources by type", the assigned IRQ number for each device is shown:

Assign exclusive Interrupt

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Since it is part of the BIOS and the operating system to distribute hardware resources, there is no way to do this manually.

Searching for a free Interrupt

Changing card slots can work to a limited extent.

In general, there are 4 legacy interrupt lines (A / B / C / D), which are alternately assigned to the PCI devices and also to the PCI slot on a main board.

There is then a mapping matrix on the hardware for these general lines, where an interrupt number is assigned to these lines.

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Of course, this only works insofar as if the devices that are need to be deactivated are not required by the system.

In this example you could try to deactivate , the "Intel Active Management" device could be deactivated.

But it can then also Nevertheless, it could happen that the next time the system is started, the system it reconfigures another device in such a way, that there is a shared interrupt sharing again.

Interrupt and CIFX Device Driver (INtime)

If the driver identifies a CIFX Card, the CIFX Card will be integrated to its administrative structure.

At the end of the initialisationinitialization, the settings from the registry are requested.

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or: Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\cifXDrv\DeviceConfig\Slot\(Slot_Number)

Activate Interrupt Mode

For the interrupt to be enabled, there must be an Interrupt assigned to the Hardware.

the The following applies here:

• Interrupt Number 0 = no Interrupt
• Interrupt Number > 0 => Phsical ⇒ Physical Interrupt Number (Legacy Interrupt : 1 - 19)
• Interrupt Number < 0 => ⇒ Message-based Interrupt Number (MSI)

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Due to the configuration and the information from the INF files for installing the hardware, the operating system is informed that the hardware does not support MSI and therefore does not receive an MSI interrupt number.

Therefore, only 0 or interrupt numbers from 1 to 19 are important here.

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In addition to the information from the hardware, the driver reads the user settings for each card from the registry in order to decide whether the interrupt should be switched on or not.

For the Handling of the Interrupt, a so-called Interrupt Thread is needed, and the Interrupt needs to be registered to the system.

If an error occurs during this process, although the interrupt was "endabledenabled" in the registry, the internal interrupt flag is deleted and the interrupt handling is "disabled".

The result can be seen in the "Board information" structure, in which "bIrqEnabled" is set to 0.

For more informations information about the "Board information" structure, please see page 18 of the following manual: cifX API (Revision 9)

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