Floating-Point Exceptions - Hitachi SH7751 Hardware Manual

Round to Zero: The digits below the round bit of the unrounded value are discarded.
If the unrounded value is larger than the maximum expressible absolute value, the value will be
the maximum expressible absolute value.
6.5

Floating-Point Exceptions

FPU-related exceptions are as follows:


General illegal instruction/slot illegal instruction exception
The exception occurs if an FPU instruction is executed when SR.FD = 1.


FPU exceptions
The exception sources are as follows:

FPU error (E): When FPSCR.DN = 0 and a denormalized number is input

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 FPSCR FPU exception cause field contains bits corresponding to all of above E, V, Z, O,
U, and I, and the FPSCR flag and enable fields contain bits corresponding to 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.


Enable/disable exception handling
The SH7751 Series supports enable exception handling and disable exception handling.
Enable exception handling is initiated in the following cases:

FPU error (E): FPSCR.DN = 0 and a denormalized number is input

Invalid operation (V): FPSCR.EN.V = 1 and (instruction = FTRV or invalid operation)

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

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

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

Inexact exception (I): FPSCR.EN.I = 1 and instruction with possibility of inexact operation
result
Rev. 3.0, 04/02, page 163 of 1064