AMD AMD-K6-2/400 User Guide - Page 260

Preliminary Information AMD-K6™-2E+ Embedded Processor Data Sheet 23542A/0-September 2000 External Logic Support of Floating-Point Exceptions The processor provides the FERR# (Floating-Point Error) and IGNNE# (Ignore Numeric Error) signals to allow the external logic to generate the interrupt in a manner consistent with IBM-compatible PC/AT systems. The assertion of FERR# indicates the occurrence of an unmasked floating-point exception resulting from the execution of a floating-point instruction. IGNNE# is used by the external hardware to control the effect of an unmasked floating-point exception. Under certain circumstances, if IGNNE# is sampled asserted, the processor ignores the floating-point exception. Figure 88 on page 239 illustrates an implementation of external logic for supporting floating-point exceptions. The following example explains the operation of the external logic in Figure 88: 1. As the result of a floating-point exception, the processor asserts FERR#. 2. The assertion of FERR# and the sampling of IGNNE# negated indicates the processor has stopped instruction execution and is waiting for an interrupt. 3. The assertion of FERR# leads to the assertion of INTR by the interrupt controller. 4. The processor acknowledges the interrupt and jumps to the corresponding interrupt service routine in which an I/O write cycle to address port F0h leads to the assertion of IGNNE#. 5. When IGNNE# is sampled asserted, the processor ignores the floating-point exception and continues instruction execution. 6. When the processor negates FERR#, the external logic negates IGNNE#. See "FERR# (Floating-Point Error)" on page 111 and "IGNNE# (Ignore Numeric Exception)" on page 116 for more details. 238 Floating-Point and Multimedia Execution Units Chapter 11