Application software notes

AN4276

16/21

DocID024408 Rev 2

Figure 8. OS exception handling with user hook

5.3

Flash memory drivers

Flash driver can easily find if data read from the memory are correct or there was a non-

correctable ECC error by reading Flash module control register MCR. There are two status

bits linked to ECC events, MCR.EDC bit signaling single bit correction and MCR.EER bit

signaling presence of non-correctable EC error during read operation. It is up to the driver

and application how it processes these events.

In any case, low level exception events are enabled and activated whenever there is a non-

correctable EC error during read access. It can have impact on processing time needed to

read the data from Flash memory by the driver.

Driver should not rely on ECSM ECC status bits that are used and controlled in low level

exception handlers and which are completely independent from the Flash driver.

There are several methods to read multiple data with ECC checking where each method

has its pros and cons.

•

Check ECC immediately after each read access

•

Check ECC after whole data buffer is read

•

Low level exception handler linked to the driver ECC check

IVOR2 exception ie.

-ECC

-MPU

- Register protection

OS IVOR2 Handler()

User IVOR2 Handler()

ECC errors

Try to correct the

ECC issue

User IVOR2

Handler() call

Shutdown

Return

UserSolved value

Shutdown

Other reason of

user interest

Return

UserNotSolved value

YES

NO

NO

UserSolved

Continue with

standard OS

handler

YES

NO

YES

NO