IBM xSeries 380, Hardware Maintenance Manual

Page: 33 / 324

Diagnostics
23
Notes:
1. Each test on the Memory menu can generate error codes.
2. Each test on the menu can be aborted by pressing <Esc>.
DMI memory fault isolation
DMI Memory Fault Isolation
AMIDiag isolates faulty memory modules. AMIDiag displays
The faulty memory chip is on SIMM x
BIOS ROM test
The BIOS ROM Test checks the data path of the BIOS ROM and makes sure the ROM
is write-protected. Select Memory from the Main Menu, select BIOS ROM Test. Press
<Enter> to start the BIOS ROM Test.
Parity test
Run this test to find bad memory locations. This test finds parity errors in all system
memory. This test is the best way to identify and report data corruption because of
DRAM system memory hardware problems. This test diagnoses the parity error
detection circuitry in DRAM.
Parity All data is stored in patterns of binary digits (1s and 0s). Each byte has eight
binary digits (bits). Parity is either even or odd. The parity of a block of data storage is
the sum of all the set binary digits in that unit. If there are eight bits in each unit (a
byte), the parity is the sum of all bits that are set to 1. PC system memory is organized
into bytes that have even or odd parity. This parity is achieved by adding a bit, called
the parity bit, which is made even or odd by the hardware circuitry to make sure all
data units have the same parity. Most system memory actually has 9 bits (8 data bits
and one parity bit). Adding a parity bit is a method of assuring that the data is correct.
Test Description ISA systems include memory parity checking circuitry. When the
CPU accesses a memory location that has a parity error, a bit is set in a specific register
and an NMI (nonmaskable interrupt) is generated. AMIDiag captures the NMI and
checks the specific register for the parity error indicator while accessing different
memory regions. If a parity error occurs in the memory area where AMIDiag is
located, the system may hang.