ECC exception handling

AN4276

12/21

DocID024408 Rev 2

4.1

RAM ECC error action

It is up to the system requirements what to do in case of non-correctable ECC error during

read access to RAM memory. Handler can decide upon analysis of additional ECSM

registers, like ECSM.REAR register determining RAM address. If the application considers

such event as critical it is up to the application to terminate the system in the managed way.

To clear non-correctable ECC error in the memory means to overwrite whole 32-bit word of

affected RAM cell with a new value that refreshes data and ECC value.

4.2

Code Flash ECC error action

Criticality of non-correctable ECC error from Code Flash memory depends on type of the

access. Error during the instruction fetch represents critical situation and can be taken as

critical event requiring system termination.

ECC error during data access can or cannot represent critical event depending on system

implementation, like data redundancy etc. In such case error action depends on system

design.

4.3

Data Flash ECC error action

Non-correctable ECC exception coming from data Flash accesses can happen regularly

and may not represent critical events especially when data Flash memory is used for

EEPROM emulation. In such case it is desired to continue the program operation and let

application software to solve the ECC data error.

In principle there are two scenarios how error handler, IVOR2 in this case, can let

application software to continue its flow.

•

Continue with successive instruction of the read function

•

Continue from known address in the read function

Both scenarios are based on SRR0 register modification which changes effective address

where to continue once the handler returns back by rfi instruction. Modification of SRR0

register is necessary because it is loaded by effective address of the instruction that caused

the exception, which means that using the original value of SRR0 would cause execution of

the same instruction accessing corrupted memory cell once returning from the handler.

4.3.1

Continue with successive instruction of the read function

Target is to continue with the instruction that follows the instruction reading the data from

Flash memory like in Figure 5.