PRB: Cyrix Processor May Cause Build Failure

• Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52
• Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0
• Fortran PowerStation for MS-DOS, Versions 1.0, 1.0a
• Fortran PowerStation 32 for NT, version 1.0, 4.0

SYMPTOMS

When building a project using one of the products mentioned above, one or more of the following problems may occur:

• The Visual Workbench may return "0 error(s), 0 warning(s)", but no executable is produced.
• From the command line, the linker may return "Run-Time Error R6000 - Stack Overflow."
• The machine may hang during a build from the command line.

CAUSE

A 386DX or 386SX computer was upgraded using the Cyrix "LC" family of processors in place of the required processor from the Cyrix "RX" family.

For the 486DRX family, an early lot number had a bad mask that exhibits a similar problem. It can be identified by the number on the top of the chip, under the heat sink. The bad lot will be xx1###x where x is a letter and # is a number. About 50% of these chips also fail due to the same timing conditions as those above.

MORE INFORMATION

Cyrix builds CPUs for both OEMs and end users that plug into 386DX and 386SX sockets. The end user CPU family is labeled 486DRx or 486SRx, while the OEM family of microprocessors is labeled 486DLC or 486SLC. The RX or end user family of microprocessors differs from the LC or OEM family as follows:

• The RX family does not require any BIOS or hardware modifications to existing 386 systems as does the LC family.
• The RX family has integrated cache coherency logic built on the chip, unlike the LC family.
• The Cyrix LC family is clearly marked "FOR OEM USE ONLY" to avoid end user confusion. This processor family should not be used in unmodified existing motherboard designs.

Using an LC family processor in a system is not safe unless the necessary hardware and BIOS modifications have been made in the design of the motherboard. These changes, although not difficult for an OEM to make, are not possible for an end user. Therefore, Cyrix does not support end users who upgrade their 386DX or SX systems using the LC family of processors. The following problems can occur when using the LC family of processors as an upgrade to a 386 system:

• Loss of data on DMA devices such as SCSI or ESDI drives due to lack of cache coherency circuitry.
• General I/O timing errors due to the I/O system being too slow for the LC family.

End users who have upgraded using the LC family of processors should return the LC processor and purchase an RX family processor. If further information is needed, Cyrix can be contacted at (214) 968-8387.