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TI486 Microprocessor - Al Kossow's Bitsavers

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Interrupts and Exceptions<br />

Figure 2-26. Error Code Format<br />

The error code format is shown in Figure 2-26 and the error code bit<br />

definitions are listed in Table 2-22. Bits 15-3 (selector index) are not<br />

meaningful if the error code was generated as the result of a page fault. The<br />

error code is always zero for double faults and alignment check exceptions.<br />

15 3 2 o<br />

Selector Index S2 S1 SO<br />

Table 2-22. Error Code Bit Definitions<br />

FAULT<br />

TYPE<br />

SELECTOR<br />

INDEX<br />

(BITS 15-3)<br />

S2 S1 SO<br />

(BIT 2) (BIT 1) (BIT 0)<br />

Page fault Reserved Fault caused by: Fault occurred during: Fault occurred during:<br />

O=not present page O=read access O=supervisor access<br />

1 =page-Ievel protection 1 =write access 1 =user access<br />

violation<br />

IDTfault Index of faulty Reserved 1 If set exception occurred<br />

IDT selector<br />

while trying to invoke<br />

exception or hardware<br />

interrupt handler.<br />

Segment Index of faulty TI bit of faulty selector 0 If set exception occurred<br />

fault selector while trying to invoke<br />

exception or hardware<br />

interrupt handler.<br />

2-50 Programming Interface

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