TMPR4956C datasheet(158/286 Pages) TOSHIBA

158 / 286 page

Chapter 8 CPU Exception

8-30

8.21.6

Saving and Restoring State

Sixteen doubleword

† coprocessor load or store operations save or restore the coprocessor floating-point

through CFC1/CTC1 instructions, and saving and restoring the processor registers. Normally, the

Control/Status

When state is restored, state information in the Control/Status register indicates the exceptions that are

pending. Writing a zero value to the Cause field of Control/Status register clears all pending exceptions,

permitting normal processing to restart after the floating-point register state is restored.

8.21.7

Trap Handlers for IEEE Standard 754 Exceptions

The IEEE Standard 754 strongly recommends that users be allowed to specify a trap handler for any of

the five standard exceptions that can compute; the trap handler can either compute or specify a substitute

result to be placed in the destination register of the operation.

By retrieving an instruction using the processor Exception Program Counter (EPC) register, the trap

handler determines:

•

exceptions occurring during the operation

•

the operation being performed

•

the destination format

On Overflow or Underflow exceptions (except for conversions), and on Inexact exceptions, the trap

handler gains access to the correctly rounded result by examining source registers and simulating the

operation in software.

On Overflow or Underflow exceptions encountered on floating-point conversions, and on Invalid

Operation and Divide-by-Zero exceptions, the trap handler gains access to the operand values by

examining the source registers of the instruction.

The IEEE Standard 754 recommends that, if enabled, the overflow and underflow traps take

precedence over a separate inexact trap. This prioritization is accomplished in software; hardware sets the

bits for both the Inexact exception and the Overflow or Underflow exception.

† 32 doublewords if the FR bit is set to 1.

TMPR4956C Datasheet(PDF) 158 Page - Toshiba Semiconductor