4

MCECC Functions

Error Logging

ECC error logging is facilitated by the Petra MCECC sector because of its internal latches. When an error (single- or double-bit) occurs in the DRAMs to which the MCECC sector is connected, it freezes the address of the error and the syndrome bits associated with the data that is in error. Each MCECC sector segment performs this logging function independently of the other. Once the MCECC sector has logged an error, it does not log any new errors that occur until the ERRLOG control/status bit has been cleared by software.

Scrub

The MCECC sector contains programmable registers and circuitry to implement the memory scrubbing function. Programmable registers determine how often the entire DRAM is scrubbed. During a scrub, the scrubber holds the memory for a programmable amount of time and then releases it for the local bus, or for a refresher if one of them is requesting local bus mastership. The scrubber then refrains from using the DRAM again for a programmable amount of time. Each scrub cycle is made up of a full 39-bit read of DRAM, a correction of any single-bit errors, and a write of the full 39 corrected bits back to the same location. If a single- or double-bit error occurs and if such interrupts are enabled in the control register, the local bus master is notified. A software bit is available to disable the read portion of the scrub cycle.

Refresh

The MCECC sector provides refresh control for the DRAM. It performs a single CAS-before-RAS refresh cycle to the two DRAM blocks approximately once every 15.6 μs.

4-8

Computer Group Literature Center Web Site

Page 256
Image 256
Motorola MVME1X7P manual Error Logging, Scrub, Refresh