Functional Description

ECC

The Petra MCECC sector pair performs single-bit error correction and double-bit error detection (SECDED). Since the SDRAM device can deliver data from incremental addresses with each clock tick (subject to boundary limitations), the Petra MCECC sector does not implement an interleaved memory architecture. The SDRAM array is 32 data bits plus seven checkbits wide. The depth is dependent on the number and type of SDRAM devices.

Cycle Types

The Petra MCECC sector always initiates burst read/write accesses to the SDRAM device. If the bus access is not a burst, the cycle is terminated early. Single- and double-byte write cycles are read-modify-write accesses, but longword write accesses require no read cycle.

Error Reporting

The Petra MCECC sector generates ECC check bits for write cycles. It also checks read data from the DRAM and corrects the data if it contains a single-bit error. If a non-correctable error occurs within the read data, the Petra MCECC sector so indicates by asserting its non-correctable error (NCE) pin.

The following paragraphs describe the actions that the MCECC sector will take in different error situations.

Single Bit Error (Cycle Type = Burst Read or Non-Burst Read)

1.Correct the data that is driven to the local MC680x0 bus.

2.Do not correct the data in DRAM. The DRAM is not corrected until the next scrub of that address, which happens only if scrubbing is enabled.

3.Terminate the cycle normally. (Assert TAto the local bus.)

4.Log the error if not already logged.

5.Notify the local MPU via interrupt, if so enabled.

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Motorola MVME1X7P manual Cycle Types, Error Reporting, Single Bit Error Cycle Type = Burst Read or Non-Burst Read