Compaq EV68A Dcache Store Second Error, Dcache Duplicate Tag Parity Error, Dcache Victim Extracts

Dcache Store Second Error

–C_ADDR contains bits [19:6] of the Dcache address of the block that contains the error (bits [42:20] of the physical address are not updated).

–DC_STAT[ECC_ERR_LD] is set.

–The load queue retries the load and rewrites the register.

–A corrected read data (CRD) error interrupt is posted, when enabled.

Note: Errors in speculative load instructions cause a CRD error interrupt to be posted but the data is not scrubbed by hardware. The PALcode cannot perform a scrub because C_STAT is zero and C_ADDR does not contain the address of the error.

8.4.2 Store Instruction (Quadword or Smaller)

A store instruction that is a quadword or smaller could invoke a Dcache ECC error, since the original quadword must be read to calculate the new check bits.

•The Mbox scrubs the original quadword and replays the write transaction.

•DC_STAT[ECC_ERR_ST] is set.

•A corrected read data (CRD) error interrupt is posted, when enabled.

8.4.3Dcache Victim Extracts

•Dcache victims with an ECC error are scrubbed as they are written into the victim data buffer.

•No status is logged.

•No exception is posted.

8.5 Dcache Store Second Error

A second store instruction error is logged when it occurs close behind the first. Neither error is corrected.

•DC_STAT[ECC_ERR_ST] is set.

•DC_STAT[SEO] is set.

•When enabled, a machine check (MCHK) is posted. The MCHK is taken when not in PALmode.

8.6Dcache Duplicate Tag Parity Error

The Dcache duplicate tag has the correct version of the Dcache coherence state for the 21264/EV68A, allowing it to be used for correct tag/status data when the Dcache tags generate a parity error. These tags are parity protected also; however, the Dcache dupli- cate tag cell is designed to be much more tolerant of soft errors. The parity generators for the duplicate tags are enabled whenever the Cbox performs a physically-indexed read transaction of eight locations in the tag array. If an error is generated, the following actions are taken:

•Dcache duplicate tag parity errors are not recoverable.

8–4 Error Detection and Error Handling 21264/EV68A Hardware Reference Manual