2.4.7 Error responses

The CCI-550 uses a combination of precise and imprecise error responses.

Precise errors are signaled on the response to the request that caused the error. Except for DVM or Evict requests, for accesses to regions that are not mapped in the address decoder, the CCI-550 generates a DECERR response. For such accesses, snoops or snoop filter updates are suppressed. The address map is platform-specific. See your platform documentation for more information.
A snoop error response to a CleanInvalid, CleanShared, or MakeInvalid transaction generates a SLVERR response to the originating device.
There are certain circumstances when it is not possible to signal an error precisely. In these cases, the CCI-550 signals an error imprecisely, using the nERRIRQ output pin. You can identify the interface that received the error response by reading the Register summary.
The following table shows the errors that are signaled as imprecise. All other sources of error are signaled precisely.

Note

An error is signaled either precisely or imprecisely, but never both.

Table 2-6 Imprecise errors

Error condition
Channel receiving error
Imprecise error indicator from
A snoop hit response with the error bit set, where data from another snooped master is returned instead of this one.
CR
Slave interface receiving the CR response.
A snoop miss response with the error bit set.
CR
Slave interface receiving the CR response.
Write access that the CCI-550 generates.
B
Master interface receiving the B response.
A snoop response with the error bit set where the snoop was generated from a WriteLineUnique or WriteUnique transaction.
CR
Master interface receiving the CR response.
A snoop response with the error bit set where the snoop was generated from a back-invalidation.
CR
Slave interface receiving the CR response.
The CCI-550 generates a precise error response for a security violation on a CCI-550 register access.
Related concepts
2.4.6 Security
Related reference
3.2 Register summary
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