Drivers, Interrupts, and Trap Explained

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Drivers, Interrupts, and Trap Explained

• COMP346/5461 - Operating Systems
• Tutorial 3.5
• Revision 1.2
• September 30, 2003

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Interrupts and Trap Revisited

• Neither interrupt nor trap are function calls!
• Interrupt is an event, or a signal (do not
  confuse with UNIX signals), notifying the system
  that something happened.
• Interrupts are not necessarily used to switch
  between processes (in scheduling), but cause a
  context swicth.
• Trap is a software interrupt, it's synchronous,
  whereas an ordinary interrupt is asynchronous.
• Trap is a CPU instruction, which is invoked when
  a user program wants either some service from an
  OS (system call) or causes an error (division by
  zero, segmentation fault, page fault, etc.)

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The Big Picture
Common Interface open, close, read, write
System Call Interface
App
App
App
App
App
User mode
SW
Kernel mode
MM
kernel
PM
PTRDD
HDDD
CDDD
int
Ready queue
Bus
CPU add mult mov
trap
HW
DMA Ctl
Mon Ctl
Ptr Ctl
CD Ctl
int (IRQ)
int
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Thats It -)