Jolix
/joh'liks/ n.,adj. 386BSD

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Porting Unix to the 386: A Practical Approach



William & Lynne Jolitz


Part of the specification also details the interrupt control mechanism that allows device interrupts to be blocked/unblocked and caught by device drivers interrupt handling code.

Interrupt Priority Level Management In the PC architecture, there is a separate interrupt level per device interrupt. These are more levels than traditional UNIX wants or needs. Instead, UNIX groups different classes of devices into interrupt priority levels that can be disabled and enabled as a group (disks, terminals, network). This is done through spl( ) function calls, named for a PDP-11/45 instruction which implemented this feature on early UNIX systems. This capability must be provided in 386BSD as well. Each interrupt vector (interrupt gate) has code that saves the cpl (current priority level) variable on the stack, sets the new cpl value, and turns on interrupts above this level. On return from the interrupt, all vectors call a common routine that disables interrupts, restores the cpl, and returns with interrupts enabled. The cpl is altered, as is the priority mask of the dual 8259 ICUs, by the spl( ) subroutines. This micro-processor or system can now be run at different priority levels on demand. <<BACK NEXT >> Tags: 386bsd | designing the software specification | porting unix to the 386 | porting unix | interrupt vector | interrupt priority levels | tags

Most Read: Most Popular: Section: Porting Unix to the 386: Designing the Software Specification Getting Started: References, Equipment, and Software Development of the 386BSD Specification The Definition of the 386BSD Specification Conflicts in Priorities 386BSD Port Goals: A Practical Approach Microprocessor and System Specification Issues 386 Memory Management Vitals Segmentation and 386BSD Kernel Linear Address Space Overhead Virtual Address Space Layout Per-Process Data Structures 386 Virtual Memory Address Translation Mechanism User to Kernel Communication Primitives Berkeley UNIX Virtual Memory System Strategy Structure of Per-Process Data (u.) Process Context Description Page Fault and Segmentation Fault Mechanism Other Processor Faults Microprocessor Idiosyncrasies System Call Interface System Specific (ISA) Issues Physical Memory Map ISA Device Controllers ISA Device Auto Configuration > Interrupt Priority Level Management Bootstrap Operation Summary: Where is 386BSD Now? Suggested Readings Return to: Porting Unix to the 386: A Practical Approach

Copyright 1989, 1990, 2006 TeleMuse Partners, William Jolitz and Lynne Jolitz