Compaq EV68A specifications Bcache Tag Parity Error, Controlling Bcache Block Parity Calculation

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.

8.7Bcache 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.

8.8Controlling Bcache Block Parity Calculation

Parity is calculated for either valid Bcache blocks or all Bcache blocks. The calculation is controlled by the value in Cbox CSR BC_VALID_MODE in the WRITE_MANY chain, as follows:

•If the MSB of BcTag_H is less than the value of Maximum PA in Table 4–13,then BC_VALID_MODE=1 and parity is calculated for only valid Bcache blocks.

•If the MSB of BcTag_H is greater than or equal to the value of Maximum PA in Table 4–13,then BC_VALID_MODE=0 and parity is calculated for all Bcache blocks.

For example, if BcTag_H[38:20] and Maximum PA is 36, then 38 is greater than or equal to 36 and BC_VALID_MODE=0 and parity is calculated for all Bcache blocks.

8.9 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.

8.9.1Icache 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.

21264/EV68A Hardware Reference Manual Error Detection and Error Handling 8–5