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System ResourcesSystem Resources
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System ResourcesSystem Resources
Interrupt Request (IRQ) ChannelsInterrupt Request (IRQ) Channels
Direct Memory Access (DMA) ChannelsDirect Memory Access (DMA) Channels
I/O Port AddressesI/O Port Addresses
Memory AddressesMemory Addresses
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Interrupt Requests (IRQs)Interrupt Requests (IRQs)
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Interrupts (IRQs)Interrupts (IRQs)
Used to signal the processor that a hardware Used to signal the processor that a hardware device needs attention.device needs attention.
Used by keyboard, mouse, modem, floppy drive, Used by keyboard, mouse, modem, floppy drive, hard drive, sound card, network card, etc.hard drive, sound card, network card, etc.
Diverts the CPU to a software driver that Diverts the CPU to a software driver that services the device that generated the interrupt.services the device that generated the interrupt.
After servicing the interrupt, the CPU returns to After servicing the interrupt, the CPU returns to whatever it was doing at the time of the interrupt.whatever it was doing at the time of the interrupt.
Device needs attention.Device needs attention.
Interrupt Controller notifies the CPU.Interrupt Controller notifies the CPU.
The CPU stores its status in memory...The CPU stores its status in memory...
… and takes care of the Interrupt.… and takes care of the Interrupt.
It then retrieves its status from memoryand picks up where it left off.
It then retrieves its status from memoryand picks up where it left off.
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8259APIC
To CPU
System Timer IRQ0
Keyboard Controller IRQ1
Available IRQ2
Serial Port 2 (COM2) IRQ3
Serial Port 1 (COM1) IRQ4
Hard Disk Controller IRQ5
Floppy Disk Controller IRQ6
Parallel Port 1 (LPT1) IRQ7
Hardware Interrupts for IBM PC/XTHardware Interrupts for IBM PC/XT
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8259APIC
To CPU
System Timer IRQ0
Keyboard Controller IRQ1
Available IRQ2
Serial Port 2 (COM2) IRQ3
Serial Port 1 (COM1) IRQ4
Hard Disk Controller IRQ5
Floppy Disk Controller IRQ6
Parallel Port 1 (LPT1) IRQ7
Interrupt Priority for IBM PC/XTInterrupt Priority for IBM PC/XT
LowestPriority
LowestPriority
HighestPriority
HighestPriority
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To CPU
8259APIC
IRQ0
IRQ1
IRQ2
IRQ3
IRQ4
IRQ5
IRQ6
IRQ7
Hardware Interrupts for IBM ATHardware Interrupts for IBM AT
8259APIC
IRQ8
IRQ9
IRQ10
IRQ11
IRQ12
IRQ13
IRQ14
IRQ15
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Default Assignments (IRQs 0-7)Default Assignments (IRQs 0-7) IRQ0IRQ0 System TimerSystem Timer
IRQ1IRQ1 Keyboard ControllerKeyboard Controller
IRQ2IRQ2 Cascade to 2nd PICCascade to 2nd PIC
IRQ3IRQ3 Serial Port 2 (COM2)Serial Port 2 (COM2)
IRQ4IRQ4 Serial Port 1 (COM1)Serial Port 1 (COM1)
IRQ5IRQ5 Sound Card or Parallel Port 2 (LPT2)Sound Card or Parallel Port 2 (LPT2)
IRQ6IRQ6 Floppy Drive ControllerFloppy Drive Controller
IRQ7IRQ7 Parallel Port 1 (LPT1)Parallel Port 1 (LPT1)
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Default Assignments (IRQs 8-15) Default Assignments (IRQs 8-15)
IRQ8IRQ8 Real Time ClockReal Time Clock
IRQ9IRQ9 AvailableAvailable
IRQ10IRQ10 AvailableAvailable
IRQ11IRQ11 AvailableAvailable
IRQ12IRQ12 PS/2 MousePS/2 Mouse
IRQ13IRQ13 Math CoprocessorMath Coprocessor
IRQ14IRQ14 Primary IDEPrimary IDE
IRQ15IRQ15 Secondary IDESecondary IDE
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To CPU
8259APIC
IRQ0
IRQ1
IRQ2
IRQ3
IRQ4
IRQ5
IRQ6
IRQ7
Interrupt Priority for IBM ATInterrupt Priority for IBM AT
8259APIC
IRQ8
IRQ9
IRQ10
IRQ11
IRQ12
IRQ13
IRQ14
IRQ15
HighestPriority
HighestPriority
LowestPriority
LowestPriority
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Priority of InterruptsPriority of Interrupts
IRQ0IRQ0
IRQ1IRQ1
– IRQ8IRQ8
– IRQ9IRQ9
– IRQ10IRQ10
– IRQ11IRQ11
– IRQ12IRQ12
– IRQ13IRQ13
– IRQ14IRQ14
– IRQ15IRQ15
IRQ3IRQ3
IRQ4IRQ4
IRQ5IRQ5
IRQ6IRQ6
IRQ7IRQ7IRQ
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What did you do with boards that What did you do with boards that required IRQ2?required IRQ2?
You used IRQ9 instead.You used IRQ9 instead.
Some boards still use the IRQ2 label.Some boards still use the IRQ2 label.
Others use a dual IRQ2/IRQ9 label.Others use a dual IRQ2/IRQ9 label.
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IRQ ConflictsIRQ Conflicts
Occur when two devices try to use the same Occur when two devices try to use the same interrupt line.interrupt line.
Will cause one or both devices to Will cause one or both devices to malfunction or the system to hang.malfunction or the system to hang.
Are resolved by changing the IRQ Are resolved by changing the IRQ assignment of one of the devices.assignment of one of the devices.
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Direct Memory Access (DMA) Direct Memory Access (DMA)
DMA allows the floppy controller to transfer data directly to memory.DMA allows the floppy controller to transfer data directly to memory.
Floppy Controller
Without DMA, the CPU grabs a couple of bytes...Without DMA, the CPU grabs a couple of bytes...
Floppy Controller Floppy Drive
… and stores them in memory… and stores them in memory
Floppy Controller Floppy Drive
DMA allows the floppy controller to transfer data directly to memory.DMA allows the floppy controller to transfer data directly to memory.
Floppy Controller Floppy Drive
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ISA/PCI Default DMA-Channel ISA/PCI Default DMA-Channel AssignmentsAssignments
0 Available None1 Available 8-bit sound2 Floppy Drive Controller3 Available LPT1 in ECP Mode4 Cascade to first DMA Controller5 Available 16-bit Sound6 Available ISA SCSI Adapter7 Available
DMA Standard Function Recommended Use
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DMA conflicts occur if two DMA conflicts occur if two devices try to use the same DMA devices try to use the same DMA
channel.channel.
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I/O Port AddressesI/O Port Addresses
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What are I/O port addresses?What are I/O port addresses?
It’s the way the CPU tells its peripherals apart.It’s the way the CPU tells its peripherals apart.
It can be thought of as hardware addresses.It can be thought of as hardware addresses.
These addresses are totally separate from memory These addresses are totally separate from memory addresses.addresses.
There are 64 K of I/O port addresses.There are 64 K of I/O port addresses.
In Hexadecimal, their addresses are 0000-FFFF.In Hexadecimal, their addresses are 0000-FFFF.
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Some Common I/O Port Some Common I/O Port Addresses.Addresses.
0060-00640060-0064 KeyboardKeyboard
02F8-02FF02F8-02FF Serial Port 2 (COM2)Serial Port 2 (COM2)
0378-037F0378-037F Parallel Port 1 (LPT1)Parallel Port 1 (LPT1)
03F8-03FF03F8-03FF Serial Port 1 (COM1)Serial Port 1 (COM1)
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Memory AddressesMemory Addresses
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Memory AddressesMemory Addresses
ROM Addresses - Many boards include ROM Addresses - Many boards include some of their software in ROM.some of their software in ROM.
RAM Addresses - Many devices require a RAM Addresses - Many devices require a small buffer RAM to hold data temporarily.small buffer RAM to hold data temporarily.
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What is a Resource Conflict?What is a Resource Conflict?
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Resource conflicts occur when two Resource conflicts occur when two devices attempt to use the same:devices attempt to use the same:
IRQ lineIRQ line
DMA channelDMA channel
I/O port addressI/O port address
ROM addressROM address
RAM addressRAM address
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What are the symptoms of a What are the symptoms of a resource conflict?resource conflict?
The system hangs.The system hangs.
A device (mouse, keyboard, printer, etc.) A device (mouse, keyboard, printer, etc.) doesn’t work.doesn’t work.
The monitor displays funny characters.The monitor displays funny characters.
The printer prints funny characters.The printer prints funny characters.
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Resolving Resource ConflictsResolving Resource Conflicts Find out which devices are conflicting.Find out which devices are conflicting.
– Manual or Instruction SheetManual or Instruction Sheet
– Software DiagnosticsSoftware Diagnostics
Change the resources of one of the conflicting devices.Change the resources of one of the conflicting devices.
– JumpersJumpers
– SetupSetup
– Control Panel (Windows 3.11)Control Panel (Windows 3.11)
– Device Manager (Windows 95 or 98) Device Manager (Windows 95 or 98)