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21264/EV68A Hardware Reference Manual
Error Detection and Error Handling 8–7
Memory/System Port Single-Bit Data Correctable ECC Error
Note: Errors in speculative load instructions cause a CRD error to be posted but
the data is not scrubbed by hardware. The PALcode cannot perform a scrub
operation because C_STAT is zero and C_ADDR does not contain the
address of the block in error.
8.9.3 Bcache Victim Read
A victim from the Bcache is written directly to the system port, without correction. The
ECC parity checker on the LSD detects the error and posts a corrected read data (CRD)
error interrupt. The Cbox error register is not updated.
8.9.3.1 Bcache Victim Read During a Dcache/Bcache Miss
While the Bcache is servicing a Dcache miss and that Bcache access is also a miss, and
an error occurs during that Bcache data access, the Cbox does not latch the error infor-
mation. However, the Mbox correction state machine is activated and it invokes a CRD
error despite the fact that no correction is performed.
The Bcache access error is written out to memory and is subsequently detected and cor-
rected by the next consumer of the data.
• No correction is made.
• No status is logged (C_STAT = 0).
• A CRD error interrupt is posted, when enabled.
8.9.3.2 Bcache Victim Read During an ECB Instruction
A victim from the Bcache that occurs while an ECB instruction is being executed is
written directly to the system port without correction. No Cbox registers are set and no
exception is taken.
8.10 Memory/System Port Single-Bit Data Correctable ECC Error
The following actions may cause memory/system port data ECC errors:
• Icache fill–data possibly used by Icache
• Dcache fill–data possibly used by a load instruction
The recovery mechanism depends on the event that caused the error.
8.10.1 Icache Fill from Memory
For an Icache fill the LSD ECC generators detect the error, and bad Icache data
parity is generated for the octaword that contains the quadword in error.
• The hardware flushes the Icache.
• C_STAT[ISTREAM_MEM_ERR] is set.
• C_ADDR contains bits [42:6] of the system memory 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.