1 System Resources

2 Interrupt Request (IRQ) Channels Interrupt Request (IRQ) Channels Direct Memory Access (DMA) Channels Direct Memory Access (DMA) Channels I/O Port Addresses I/O Port Addresses Memory Addresses Memory Addresses

3 Interrupt Requests (IRQs)

4 Interrupts (IRQs) Used to signal the processor that a hardware device needs attention. Used to signal the processor that a hardware device needs attention. Used by keyboard, mouse, modem, floppy drive, hard drive, sound card, network card, etc. Used by keyboard, mouse, modem, floppy drive, hard drive, sound card, network card, etc. Diverts the CPU to a software driver that services the device that generated the interrupt. Diverts the CPU to a software driver that services the device that generated the interrupt. After servicing the interrupt, the CPU returns to whatever it was doing at the time of the interrupt. After servicing the interrupt, the CPU returns to whatever it was doing at the time of the interrupt.

Device needs attention.

Interrupt Controller notifies the CPU.

The CPU stores its status in memory...

… and takes care of the Interrupt.

It then retrieves its status from memory and picks up where it left off. It then retrieves its status from memory and picks up where it left off.

A PIC 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/XT

A PIC 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/XT Lowest Priority Lowest Priority Highest Priority Highest Priority

13 To CPU 8259A PIC IRQ0 IRQ1 IRQ2 IRQ3 IRQ4 IRQ5 IRQ6 IRQ7 Hardware Interrupts for IBM AT 8259A PIC IRQ8 IRQ9 IRQ10 IRQ11 IRQ12 IRQ13 IRQ14 IRQ15

14 Default Assignments (IRQs 0-7) IRQ0System Timer IRQ0System Timer IRQ1Keyboard Controller IRQ1Keyboard Controller IRQ2Cascade to 2nd PIC IRQ2Cascade to 2nd PIC IRQ3Serial Port 2 (COM2) IRQ3Serial Port 2 (COM2) IRQ4Serial Port 1 (COM1) IRQ4Serial Port 1 (COM1) IRQ5Sound Card or Parallel Port 2 (LPT2) IRQ5Sound Card or Parallel Port 2 (LPT2) IRQ6Floppy Drive Controller IRQ6Floppy Drive Controller IRQ7Parallel Port 1 (LPT1) IRQ7Parallel Port 1 (LPT1)

15 Default Assignments (IRQs 8-15) IRQ8Real Time Clock IRQ8Real Time Clock IRQ9Available IRQ9Available IRQ10Available IRQ10Available IRQ11Available IRQ11Available IRQ12PS/2 Mouse IRQ12PS/2 Mouse IRQ13Math Coprocessor IRQ13Math Coprocessor IRQ14Primary IDE IRQ14Primary IDE IRQ15Secondary IDE IRQ15Secondary IDE

16 To CPU 8259A PIC IRQ0 IRQ1 IRQ2 IRQ3 IRQ4 IRQ5 IRQ6 IRQ7 Interrupt Priority for IBM AT 8259A PIC IRQ8 IRQ9 IRQ10 IRQ11 IRQ12 IRQ13 IRQ14 IRQ15 Highest Priority Highest Priority Lowest Priority Lowest Priority

17 Priority of Interrupts IRQ0 IRQ0 IRQ1 IRQ1 –IRQ8 –IRQ9 –IRQ10 –IRQ11 –IRQ12 –IRQ13 –IRQ14 –IRQ15 IRQ3 IRQ3 IRQ4 IRQ4 IRQ5 IRQ5 IRQ6 IRQ6 IRQ7 IRQ7 IRQ2

18 What did you do with boards that 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.

19 IRQ Conflicts Occur when two devices try to use the same interrupt line. Occur when two devices try to use the same interrupt line. Will cause one or both devices to malfunction or the system to hang. Will cause one or both devices to malfunction or the system to hang. Are resolved by changing the IRQ assignment of one of the devices. Are resolved by changing the IRQ assignment of one of the devices.

20 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 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

25 ISA/PCI Default DMA-Channel Assignments 0AvailableNone 1Available8-bit sound 2Floppy Drive Controller 3AvailableLPT1 in ECP Mode 4Cascade to first DMA Controller 5Available16-bit Sound 6AvailableISA SCSI Adapter 7Available DMA Standard FunctionRecommended Use

26 DMA conflicts occur if two devices try to use the same DMA channel.

27 I/O Port Addresses

28 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 addresses. These addresses are totally separate from memory 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.

29 Some Common I/O Port Addresses Keyboard Keyboard 02F8-02FFSerial Port 2 (COM2) 02F8-02FFSerial Port 2 (COM2) FParallel Port 1 (LPT1) FParallel Port 1 (LPT1) 03F8-03FFSerial Port 1 (COM1) 03F8-03FFSerial Port 1 (COM1)

30 Memory Addresses

31 Memory Addresses ROM Addresses - Many boards include some of their software in ROM. ROM Addresses - Many boards include some of their software in ROM. RAM Addresses - Many devices require a small buffer RAM to hold data temporarily. RAM Addresses - Many devices require a small buffer RAM to hold data temporarily.

32 What is a Resource Conflict?

33 Resource conflicts occur when two devices attempt to use the same: IRQ line IRQ line DMA channel DMA channel I/O port address I/O port address ROM address ROM address RAM address RAM address

34 What are the symptoms of a resource conflict? The system hangs. The system hangs. A device (mouse, keyboard, printer, etc.) doesn’t work. A device (mouse, keyboard, printer, etc.) doesn’t work. The monitor displays funny characters. The monitor displays funny characters. The printer prints funny characters. The printer prints funny characters.

35 Resolving Resource Conflicts Find out which devices are conflicting. Find out which devices are conflicting. –Manual or Instruction Sheet –Software Diagnostics Change the resources of one of the conflicting devices. Change the resources of one of the conflicting devices. –Jumpers –Setup –Control Panel (Windows 3.11) –Device Manager (Windows 95 or 98)