Editing Diagnostic Serial Console (section)

== Memory Testing Algorithms and Diagnostic Procedures ==

=== Automatic Memory Detection and Configuration ===

During Power-On Self Test (POST), the Glue Logic (UI8) initiates system reset and address decode validation while the 68030 CPU performs basic memory access at reset vectors. The memory controller validates SIMM presence and configuration, followed by System ROM execution of built-in diagnostic routines and video memory allocation reserving 1MB from the available RAM pool. Bank detection and validation occurs automatically for installed SIMM configuration, with memory allocation optimization based on available modules and address bus integrity testing through POST sequences.

The diagnostic system reports memory configuration through hexadecimal codes that reflect addressing architecture. A typical 4MB configuration produces the diagnostic code <code>004000000000</code>, where the significant portion <code>00400</code> converts to 4,194,304 bytes (exactly 4MB). The trailing zeros <code>0000000000</code> likely represent diagnostic status information, error flags, or formatting padding used by Apple's diagnostic tools rather than additional memory size data.

=== Manual Memory Testing Command Sequences ===

Pattern testing algorithms include Walking Ones Tests using the 32-bit sequence 0x00000001, 0x00000002, 0x00000004, 0x00000008, continuing through all 32 bit positions to 0x40000000, 0x80000000, designed to detect stuck address bits and adjacent bit interference. Walking Zeros Tests employ the inverse pattern sequence 0xFFFFFFFE, 0xFFFFFFFD, 0xFFFFFFFB, 0xFFFFFFF7, continuing through all inverse positions to 0xBFFFFFFF, 0x7FFFFFFF, identifying stuck-at-one faults and coupling issues.

The March C- Algorithm implementation follows these steps: initialize all memory locations with 0s, read 0 and write 1 in ascending address order, read 1 and write 0 in ascending address order, read 0 and write 1 in descending address order, read 1 and write 0 in descending address order, and conclude with read 0 verification pass in descending addresses. This comprehensive algorithm detects various memory cell failure modes including data retention, coupling effects, and address decode problems.