CRC checksum over PMU0 and PMU1 in TC1798

[Matthias R. (Firma: Boschrexroth) (roettgermann)]

Hello,
until now in TC1798 we use the first flash (PMU0) with header and footer 
and CRC-building.
In TC1798 there is a gap between PMU0 and PMU1.
Problem: now we want use also the PMU1 (but not always), so we don't 
know whether PMU1 is used and so we don't know footer / header for 
CRC-Building exactly?
The main point is: what would you suggest how we could handle the 
reserved parts?
Would it be better to
- build two checksums over each part?
- build a checksum within the reserved parts? ( I don't think so ....)
- build a checksum and left out the reserved parts (but how).

I would be glad if anyone could help me.
Regards Matthias