How STCU2 configuration can be updated
TN1239
4/11
DocID029694 Rev 1
2
How STCU2 configuration can be updated
As explained in the previous chapter, simply writing a second STCU configuration at
different location does not cause any change in the configuration that the STCU loads, such
as the first one.
Since the UTest sector is not erasable, if the user wants to change the STCU configuration
he must invalidate the first configuration. It means invalidating the first instance of the unlock
keys.
As a consequence, STCU2 reads unlock keys that are not correct and ignores the following
configuration.
With reference to
, if the user invalidates the unlock keys at address X the STCU
ignores the first configuration and loads the second one.
If needed, the user can repeat the process by adding a third configuration and invalidating
the unlock keys at address Y and so forth.
Figure 2. Make STCU unlock key invalid
Invalidating means overwriting the unlock keys with incorrect keys. The user, however, does
this operation carefully due to the ECC/EDC.
The ECC/EDC protects the UTest content. It means that the UTest contains not only the
data, but also some redundant bits. The hardware can correct or detect some errors by
comparing the data and the redundant bits. This process is transparent from the standpoint
of the user who cannot access the redundant bits.
For this reason, if the user overwrites the unlock keys with random data, there is a risk that
the ECC/EDC logic detects one or more not correctable errors. In case of this event the
sample does not start.
Under those circumstances, the user must adopt specific values that do not cause the
ECC/EDC errors. These values are visible in
