You can upgrade to CTPOS 9.1R3.1 from older releases (7.x and
9.x) by using the dual image upgrade procedure only. The traditional
upgrade using the "upgrade" utility will not be supported for upgrading
CTPOS 9.1R3.1 from earlier releases ( 7.x and 9.x). Refer
to the Upgrading to CTPOS 9.1R3.1
The dual image feature is supported on the CTP150, CTP151, and CTP2000 (only PP332 and PP833 processors are supported, PP310 is not supported) platforms.
The dual image upgrade feature is supported on CTPOS 7.3R7-1 and above including 9.0R1, 9.1R1 and 9.1R2 releases. If you want to upgrade an older CTP, then you need to first upgrade to one of these releases.
There are a few older generation PP332 CPUs which will not support 9.1R3.1. The installation process will detect such CPUs and prevent the upgrade.