7.3 -Flags

7. Floating-Point Exceptions

7.3 Flags

A Flag bit is provided for each IEEE exception. This Flag bit is set to a 1 on the assertion of its corresponding exception, with no corresponding exception trap signaled.

The Flag bit is reset by writing a new value into the Status register; flags can be saved and restored by software either individually or as a group.

When no exception trap is signaled, floating-point coprocessor takes a default action, providing a substitute value for the exception-causing result of the floating-point operation. The particular default action taken depends upon the type of exception. Table 7-1 lists the default action taken by the FPU for each of the IEEE exceptions.

Table 7-1 Default FPU Exception Actions

The FPU detects the eight exception causes internally. When the FPU encounters one of these unusual situations, it causes either an IEEE exception or an Unimplemented Operation exception (E).

Table 7-2 lists the exception-causing situations and contrasts the behavior of the FPU with the requirements of the IEEE Standard 754.

Table 7-2 FPU Exception-Causing Conditions

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