SH7672 datasheet(112/1292 Pages) RENESAS

112 / 1292 page

Section 3

Floating-Point Unit (FPU)

Rev. 1.00

Nov. 14, 2007

Page 86 of 1262

REJ09B0437-0100

3.5.2

FPU Exception Handling

FPU exception handling is initiated in the following cases:

• FPU error (E): FPSCR.DN = 0 and a denormalized number is input (No error occurs in the

SH2A-FPU)

• Invalid operation (V): FPSCR.Enable.V = 1 and invalid operation

• Division by zero (Z): FPSCR.Enable.Z = 1 and division with a zero divisor

• Overflow (O): FPSCR.Enable.O = 1 and instruction with possibility of operation result

overflow

• Underflow (U): FPSCR.Enable.U = 1 and instruction with possibility of operation result

underflow

• Inexact exception (I): FPSCR.Enable.I = 1 and instruction with possibility of inexact operation

result

These possibilities are shown in the individual instruction descriptions. All exception events that

originate in the FPU are assigned as the same exception event. The meaning of an exception is

determined by software by reading from FPSCR and interpreting the information it contains. If no

bits are set in the FPU exception cause field of FPSCR when one or more of bits O, U, I, and V are

set in the FPU exception enable field, this indicates that an actual exception source is not

generated. Also, the destination register is not changed by any FPU exception handling operation.

Except for the above, the FPU disables exception handling. In every processing, the bit

corresponding to source V, Z, O, U, or I is set to 1, and a default value is generated as the

operation result.

• Invalid operation (V): qNaN is generated as the result.

• Division by zero (Z): Infinity with the same sign as the unrounded value is generated.

• Overflow (O):

When rounding mode = RZ, the maximum normalized number, with the same sign as the

unrounded value, is generated.

When rounding mode = RN, infinity with the same sign as the unrounded value is generated.

• Underflow (U):

Zero with the same sign as the unrounded value is generated.

• Inexact exception (I): An inexact result is generated.

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