FCO DEQNA-R001, Undetected data corruptions occur

This document, Field Change Order (FCO) DEQNA-R001, addresses critical issues of undetected data corruptions and device "lock-ups" occurring in DEQNA (M7504) modules operating at revision level "D" or earlier within Micro-PDP11 and Micro-VAX LSI-Bus Ethernet systems. The problems manifest when the DEQNA is busy with a transmit pre-fill operation while receiving a message, requiring a device or system reset to clear.

The solution involves both a hardware upgrade and recommended software modifications. The hardware fix mandates replacing all M7504 (DEQNA) modules below Rev "E1/E2" with upgraded, reworked devices (M7504 ("E1/E2")). Modules can be identified by the presence of chip # 23-087K4-00 in location E11 or by a revision stamp.

For custom DEQNA device drivers, the document provides essential software change recommendations to prevent future issues. These include configuring a sufficient number (at least 20) and size (sum exceeding 1600 bytes, individual buffers at least 1600 bytes for safety) of receive buffers, and ensuring both receive and transmit buffers start on word-aligned boundaries. Specific guidelines are also given for setting up Buffer Descriptor Lists (BDLs), managing transmit packet sizes (not exceeding 1518 bytes), and implementing appropriate timers and checks within transmit and receive service routines. Digital's standard operating system drivers for various platforms (e.g., MicroVMS, Ultrix, VAXELN, DECnet) have already incorporated these recommended changes.

The rework procedure outlines steps for safely replacing the DEQNA module, including powering down the system, removing the old module, verifying the new module's revision, and crucially, exchanging the Ethernet Address ROM from the old module to the new one to preserve the system's node address. The old module must be tagged and returned for rework. Following installation, system and device diagnostics, along with customer verification of operating system software, are required to confirm resolution. The FCO was released on June 4, 1986, with an estimated installation time of 1.0 hour and affecting an estimated 30,000 systems.