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Alpha 21264/EV67 Hardware Reference Manual
Error Detection and Error Handling 8–5
Bcache Tag Parity Error
• C_STAT[DC_PERR] is set.
• C_ADDR contains bits [42:6] of the Dcache duplicate tag address of the block that
contains the error.
• When enabled, a machine check (MCHK) is posted. The MCHK is taken when not
in PALmode.
8.7 Bcache Tag Parity Error
The Bcache tag parity is checked on all Bcache tag references, including references
invoked by system probes. If an error is detected, the following actions are taken:
• Bcache tag parity errors are not recoverable.
• C_STAT[BC_PERR] is set.
• C_ADDR contains bits [42:6] of the Bcache address of the block that contains the
error.
• When enabled, a machine check (MCHK) is posted. The MCHK is taken when not
in PALmode.
8.8 Bcache Data Single-Bit Correctable ECC Error
The following actions may trigger Bcache data ECC errors:
• Icache fill, data possibly used by Icache
• Dcache fill, data possibly used by load instruction
• Bcache victim during an ECB instruction or during a Dcache/Bcache miss
The recovery mechanism depends on the action that triggered the error.
8.8.1 Icache Fill from Bcache
For an Icache fill, the LSD ECC checkers detect the error, and bad Icache data parity is
generated for the octaword that contains the quadword in error. If an error is detected,
the following actions are taken:
• The hardware flushes the Icache.
• C_STAT[ISTREAM_BC_ERR] is set.
• C_ADDR contains bits [42:6] of the Bcache fill address of the block that contains
the error.
• C_SYNDROME_0[7:0] and C_SYNDROME_1[7:0] contain the syndrome of
quadword 0 and 1, respectively, of the octaword subblock that contains the error.
• A machine check (MCHK) is posted and taken immediately. The PALcode machine
check handler performs a scrubbing operation as described in Section D.36 to
ensure that the origination point of the error is corrected.
Note: A corrected read data (CRD) error interrupt is also posted in case this error
is in a speculative path and the MCHK is removed. The CRD PALcode
reads the status, to detect this condition, and scrubs the block. In the normal
MCHK flow, the PALcode clears the pending CRD error.