Section 5 Exception Handling
Rev. 0.50 May 18, 2006 Page 118 of 1588
REJ09B0313-0050
5.6.6
Floating Point Operation Instructions
An FPU exception is generated when the V, Z, O, U or I bit in the FPU enable field (Enable) of
the floating point status/control register (FPSCR) is set. This indicates the occurrence of an invalid
operation exception defined by the IEEE standard 754, a division-by-zero exception, overflow (in
the case of an instruction for which this is possible), underflow (in the case of an instruction for
which this is possible), or inexact exception (in the case of an instruction for which this is
possible).
The instructions that may cause an exception are FADD, FSUB, FMUL, FDIV, FMAC,
FCMP/EQ, FCMP/GT, FLOAT, FTRC, FCNVDS, FCNVSD, and FSQRT.
An FPU exception is generated only when the corresponding enable bit is set. When the FPU
detects an exception source, FPU operation is halted and exception generation is reported to the
CPU. When exception handling is started, the CPU operations are as follows.
1. The start address of the exception service routine which corresponds to the FPU exception that
occurred is fetched from the exception handling vector table.
2. The status register (SR) is saved to the stack.
3. The program counter (PC) is saved to the stack. The PC value saved is the start address of the
instruction to be executed after the last executed instruction.
4. After jumping to the address fetched from the exception handling vector table, program
execution starts. This jump is not a delayed branch.
The FPU exception flag field (Flag) of FPSCR is always updated regardless of whether or not an
FPU exception has been accepted, and remains set until explicitly cleared by the user through an
instruction. The FPU exception source field (Cause) of FPSCR changes each time an FPU
instruction is executed.
When the V bit in the FPU exception enable field (Enable) of FPSCR is set and the QIS bit in
FPSCR is also set, FPU exception is generated when qNAN or
±∞
is input to a floating point
operation instruction source.
Содержание Single-Chip Microcomputer SH7203
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Страница 1598: ...Section 31 Electrical Characteristics Rev 0 50 May 18 2006 Page 1568 of 1588 REJ09B0313 0050 ...
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