Specification Update

MOBILE INTEL

CELERON

PROCESSOR at 466 MHz, 433 MHz, 400 MHz,

366 MHz, 333 MHz, 300 MHz, 266 MHz SPECIFICATION UPDATE

ERRATA

H1. FP Data Operand Pointer May Be Incorrectly Calculated After

FP Access Which Wraps 64-Kbyte Boundary in 16-Bit Code

Problem: The FP Data Operand Pointer is the effective address of the operand associated with the last

noncontrol floating-point instruction executed by the machine. If an 80-bit floating-point access (load or store)

occurs in a 16-bit mode other than protected mode (in which case the access will produce a segment limit

violation), the memory access wraps a 64-Kbyte boundary, and the floating-point environment is subsequently

saved, the value contained in the FP Data Operand Pointer may be incorrect.

Implication:

A 32-bit operating system running 16-bit floating-point code may encounter this erratum, under

the following conditions:

• The operating system is using a segment greater than 64 Kbytes in size.

• An application is running in a 16-bit mode other than protected mode.

• An 80-bit floating-point load or store which wraps the 64-Kbyte boundary is executed.

• The operating system performs a floating-point environment store (FSAVE/FNSAVE/FSTENV/FNSTENV)

after the above memory access.

• The operating system uses the value contained in the FP Data Operand Pointer.

Wrapping an 80-bit floating-point load around a segment boundary in this way is not a normal programming

practice. Intel has not currently identified any software which exhibits this behavior.

Workaround: If the FP Data Operand Pointer is used in an OS which may run 16-bit floating-point code, care

must be taken to ensure that no 80-bit floating-point accesses are wrapped around a 64-Kbyte boundary.

Status: For the steppings affected see the Summary of Changes at the

beginning of this section.