Double-Bit Fill Errors

8.11 Double-Bit Fill Errors

Double-bit errors for fills are detected, but not corrected, in the 21264/EV67. The fol- lowing events may cause a double-bit fill error:

Icache fill from Bcache

Dcache fill from Bcache

Icache fill from memory

Dcache fill from memory

If an error is detected, the following actions are taken:

C_STAT is set to one of the following: ISTREAM_BC_DBL (Icache fill from Bcache) DSTEAM_BC_DBL (Dcache fill from Bcache) ISTREAM_MEM_DBL (Icache fill from memory) DSTREAM_MEM_DBL (Dcache fill from memory)

C_ADDR contains bits [42:6] of the system memory fill address of the block that contains the error.

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

A double-bit fill error from memory, marked by the data’s corresponding ECC, when written to cache, also writes the corresponding ECC to cache. Any consumer of that error (such as another CPU) also consumes the corresponding ECC value.

Note: C_ADDR may be inaccurate in heavy traffic conditions. C_STAT is accu- rate.

8.12 Error Case Summary

Table 8–3summarizes the various error cases and their ramifications.

Table 8–3 Error Case Summary

 

 

 

Hardware

 

Error

Exception

Status

Action

PALcode Action

 

 

 

 

 

Icache data or tag

CRD

ISTAT[PAR]

Icache flushed

Log as CRD

parity error

 

 

 

 

Dcache tag parity

DFAULT

MM_STAT[DC_TAG_PERR]

Evict with two

error (on issue)

 

VA[address]

 

HW_LDs and log as

 

 

 

 

CRD

Dcache tag parity

MCHK1

DC_STAT[TPERR_P0] or

Log as MCHK

error (on retry)

 

DC_STAT[TPERR_P1]

 

 

Dcache single-bit

CRD

DC_STAT[ECC_ERR_LD]

Corrected and

Log as CRD

ECC error on load

 

C_STAT[DSTREAM_DC_ERR]

scrubbed

 

 

 

C_ADDR[bits [19:6] of the error

 

 

 

 

address. [42:20] not updated.]

 

 

Alpha 21264/EV67 Hardware Reference Manual

Error Detection and Error Handling 8–9

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Compaq 21264, EV67 Double-Bit Fill Errors, Error Case Summary, 3summarizes the various error cases and their ramifications