Compaq 21264 - Manual (Page 237)

Alpha 21264/EV67 Hardware Reference Manual Error Detection and Error Handling 8–9
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 8–3 summarizes the various error cases and their ramifications.
Table 8–3 Error Case Summary
Error Exception Status
Hardware
Action
PALcode Action
Icache data or tag
parity error CRD ISTAT[PAR] Icache flushed Log as CRD
Dcache tag parity
error (on issue) DFAULT MM_STAT[DC_TAG_PERR]
VA[address] — Evict with two
HW_LDs and log as
CRD
Dcache tag parity
error (on retry) MCHK
1
DC_STAT[TPERR_P0] or
DC_STAT[TPERR_P1] — Log as MCHK
Dcache single-bit
ECC error on load CRD DC_STAT[ECC_ERR_LD]
C_STAT[DSTREAM_DC_ERR]
C_ADDR[bits [19:6] of the error
address. [42:20] not updated.] Corrected and
scrubbed Log as CRD