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Unformatted text preview: e FERR# output. 3. The frozen processor waits for an external interrupt, which must be supplied by external hardware in response to the FERR# assertion. 4. In MS-DOS compatibility systems, FERR# is fed to the IRQ13 input in the cascaded PIC. The PIC generates interrupt 75H, which then branches to interrupt 2, as described earlier in this appendix for systems using the Intel 286 and Intel 287 or Intel386 and Intel 387 processors. The deferred method of error reporting is used for all exceptions caused by the basic arithmetic instructions (including FADD, FSUB, FMUL, FDIV, FSQRT, FCOM and FUCOM), for precision exceptions caused by all types of x87 FPU instructions, and for numeric underflow and overflow exceptions caused by all types of x87 FPU instructions except stores to memory. D-4 Vol. 1 GUIDELINES FOR WRITING X87 FPU EXCEPTION HANDLERS Some x87 FPU instructions with some x87 FPU exceptions use an "immediate" method of reporting errors. Here, the FERR# is asserted immediately, at the time that the exception occurs. The immediate method of error reporting is used for x87 FPU stack fault, invalid operation and denormal exceptions caused by all transcendental instructions, FSCALE, FXTRACT, FPREM and others, and all exceptions (except precision) when caused by x87 FPU store instructions. Like deferred error reporting, immediate error reporting will cause the processor to freeze just before executing the next WAIT or x87 FPU instruction if the error condition has not been cleared by that time. Note that in general, whether deferred or immediate error reporting is used for an x87 FPU exception depends both on which exception occurred and which instruction caused that exception. A complete specification of these cases, which applies to both the Pentium and the Intel486 processors, is given in Section 5.1.21 in the Pentium Processor Family Developer's Manual: Volume 1. If NE = 0 but the IGNNE# input is active while an unmasked x87 FPU exception is in effect, the processor disregards the exception, does not assert FERR#, and continues. If IGNNE# is then de-asserted and the x87 FPU exception has not been cleared, the processor will respond as described above. (That is, an immediate exception case will assert FERR# immediately. A deferred exception case will assert FERR# and freeze just before the next x87 FPU or WAIT instruction.) The assertion of IGNNE# is intended for use only inside the x87 FPU exception handler, where it is needed if one wants to execute non-control x87 FPU instructions for diagnosis, before clearing the exception condition. When IGNNE# is asserted inside the exception handler, a preceding x87 FPU exception has already caused FERR# to be asserted, and the external interrupt hardware has responded, but IGNNE# assertion still prevents the freeze at x87 FPU instructions. Note that if IGNNE# is left active outside of the x87 FPU exception handler, additional x87 FPU instructions may be executed after a given instruction has caused...
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This note was uploaded on 10/01/2013 for the course CPE 103 taught by Professor Watlins during the Winter '11 term at Mississippi State.
- Winter '11