Single-Bit Error Detection - Intel IXP45X Developer's Manual

11.4.1

Single-Bit Error Detection

When enabled, the MCU interrupts the core when the ECC logic detects a single-bit
error by setting the appropriate bit in the MCISR register. The Intel XScale processor
knows the interrupt was caused by a single-bit error by polling the ELOG0 or ELOG1
register. The DDRI SDRAM Control Block ensures that correct data is returned but the
interrupt handler is responsible for scrubbing the error in the array (refer to
"Scrubbing" on page
An example flow for a single-bit error with error detection and reporting enabled is:
• A single-bit ECC error is detected on the data bus by the MCU.
• The MCU fixes the error prior to returning the data.
• The MCU clears ELOG0[8] indicating a single-bit error.
• The MCU records the requester of the transaction that resulted in an error in
ELOG0[23:16]
• The MCU loads ELOG0[7:0] with the syndrome that indicated the error.
• The MCU loads ECAR0[31:2] with the address where the error occurred.
• Since the Intel XScale processor needs to scrub the error in the array, the MCU sets
MCISR[0] to 1 (assuming it is not already set).
— Setting any bit in the MCISR causes an interrupt to the Intel XScale processor.
• Software polls the interrupt status register. Bit 0 set to 1 indicates that the first
error has occurred.
• Software polls ELOG0 and ECAR0 and scrubs the error at the location specified by
ECAR0.
• Software writes a 1 to MCISR[0] thereby clearing it.
If software does not perform error scrubbing, the probability of an unrecoverable multi-
bit error increases for the memory location containing the single-bit error.
ECARx and ELOGx remain registered until software explicitly clears them.
If a second error occurs before software clears the first by resetting MCISR[0] or
MCISR[1], the error is recorded in the remaining ELOGx/ECARx register. If none are
available, the error is not logged but the MCU carries out the action described in
Table 214.
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IXP46X Product Line of Network Processors—Memory Controller
August 2006
Order Number: 306262-004US