SH7261 datasheet(107/1348 Pages) RENESAS

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Section 3 Floating-Point Unit (FPU)

Rev. 2.00 Sep. 07, 2007 Page 75 of 1312

REJ09B0320-0200

3.5

Floating-Point Exceptions

3.5.1

FPU Exception Sources

The exception sources are as follows:

• FPU error (E): When FPSCR.DN = 0 and a denormalized number is input (No chance to occur

in the SH2A-FPU)

• Invalid operation (V): In case of an invalid operation, such as NaN input

• Division by zero (Z): Division with a zero divisor

• Overflow (O): When the operation result overflows

• Underflow (U): When the operation result underflows

• Inexact exception (I): When overflow, underflow, or rounding occurs

The FPU exception cause field in FPSCR contains bits corresponding to all of above sources E, V,

Z, O, U, and I, and the FPU exception flag and enable fields in FPSCR contain bits corresponding

to sources V, Z, O, U, and I, but not E. Thus, FPU errors cannot be disabled.

When an FPU exception occurs, the corresponding bit in the FPU exception cause field is set to 1,

and 1 is added to the corresponding bit in the FPU exception flag field. When an FPU exception

does not occur, the corresponding bit in the FPU exception cause field is cleared to 0, but the

corresponding bit in the FPU exception flag field remains unchanged.

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 chance to occur 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

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