Extra Notes

Interrupt Processing

Hardware

• Tests for interrupt signal, and removes the signal if there is one
• Saves the PSW and the location of the next instruction onto a control stack
• Load the program counter with the location of the interrupt handler routine
• After the routine is finished, restore the PSW and PC

Software

• Saves the contents of all registers onto the stack
• PC updated to the beginning of the routine
• Processes the interrupt
• Restores all the register values

I/O Tables

• Manage the I/O devices and channels of the computer system
• Maintains the status of the I/O operation and the location in main memory being used as the source/destination of the I/O transfer

Process Control Block

• Unqiue identifier
• State
• Priority
• Program counter (next instruction in the process)
• Memory pointers
• Context data
• I/O status information
• Accounting information

Microkernel

• Kernel only performs vital functions
• Server provides the rest
• Servers can run in user mode
• Decouples kernel and server development

Messaging Examples

Non-blocking send - concurrent programs, printing

Block receive - more natural on concurrent programs

• May be blocked indefinetly if the message is lost

Linux Process Diagram

Running - executing or ready to execute

Interruptible - a blocked state; the process is waiting for an event, so as the end of an I/O operation, the availability of a resource, or a signal from another process

Uninterruptible - a blocked state; process is waiting directly on hardware conditions and does not receive any signals

Stopped - the process has been halted an can only resume by positive action from another process. For example, a process

Zombie - the process is terminated but still has it's task structure in the process table