PRB: Cause of Trap 0002 Errors

  - Microsoft SQL Server version 4.2 for OS/2

SYMPTOMS

A trap 2 error may occur periodically on SQL Server, halting all processing and causing the machine to be rebooted.

CAUSE

Trap 2, also known as a nonmaskable interrupt, is a hardware problem.

There is parity logic that monitors each memory reference on the memory subsystem of all PCs. If a parity error is encountered, the NMI (nonmaskable interrupt) pin of the Intel processor is asserted. This immediately causes control to be transferred to a short routine that prints out register information, and then halts the CPU.

There is an ISA bus signal called IOCHCK (I/O channel check) that can be asserted by any adapter card. IOCHCK is intended for use by adapter cards as a means of notifying the CPU that an off-motherboard memory parity error has occurred. IOCHCK is gated to NMI, and results in essentially the same outcome. The interrupt service routine can query a register and determine whether the parity error is from the motherboard or adapter card.

The IOCHCK signal is sometimes incorrectly used by certain video cards to trigger a desired software routine. If the software routine is not loaded correctly, the system will halt with a trap 2 error.

A variety of hardware configuration problems can also create a trap 2 condition, either by incorrectly asserting IOCHCK, or by fooling the motherboard parity logic into thinking a true parity error occurred. For example, if adapter cards containing RAM are configured with conflicting memory footprints with respect to each other or to the motherboard, a trap 2 parity error can result.

Running memory diagnostics for a period of time without failure does not indicate a properly functioning system.

PC memory subsystem design virtually guarantees any OS/2 trap 2 is a hardware problem. Resolution of this condition should center on replacing the failing memory, or resolving a possible hardware configuration problem.

WORKAROUND

Trap 2 is an OS/2 fatal error caused by a hardware problem. It is not a SQL Server, OS/2, or application software error.