AMD AMD5K86 - INIT (Initialization)

AMD~
18524B/O-Marl996 AMD5~6 Processor Technical Reference Manual
5.1.30 ICNNE (Ignore Numeric Error)
Summary
Sampled
Details
Signal Descriptions
Input
The IGNNE input, together with the numeric error (NE) bit in
CRO, controls the behavior of the FERR output where the pro-
cessor reports errors for DOS-compatible, floating-point pro-
grams.
The processor samples IGNNE every clock during memory
cycles (including cache writethroughs and writebacks), cache
hits of all types, 110 cycles, locked cycles, special bus cycles,
and interrupt acknowledge operations in the normal operating
modes (Real, Protected, and Virtual-8086) and in SMM; or
while AHOLD, BOFF, or HLDA is asserted. IGNNE is not sam-
pled in the Shutdown, Halt, Stop Grant, or Stop Clock states; or
while RESET, INIT, or PRDY is asserted.
System logic can drive the signal either synchronously or asyn-
chronously (see the data sheet for synchronously driven setup
and hold times).
The FERR and IGNNE signals are designed for backward-com-
patibility with floating-point software designed for 286 and 386
IBM-compatible PC/AT systems running DOS.
If software has cleared the numeric error (NE) bit in CRO to 0,
unmasked floating-point exception reporting depends on the
state of the IGNNE input, as follows:
• If the IGNNE input is negated, the processor reports
unmasked floating-point exception conditions in a way that
is compatible with PC/AT systems-the processor asserts
FERR to report the error externally to a busy latch. The
external busy latch generates IRQ13 if FERR is asserted,
and the service routine for IRQ13 can then assert IGNNE to
permit continued processing of floating-point instructions.
• If the IGNNE input is asserted, FERR is negated and the pro-
cessor does not report unmasked floating-point exceptio.n
conditions externally.
IGNNE plays no part in error reporting if the NE bit in CRO is
set to 1. DOS and Windows-compatible PCs typically clear the
NE bit to O. Operating systems like Windows NT set the NE bit
to 1. For additional details on the relation between FERR and
IGNNE, see the description of the FERR signal on page 5-65.
5-81