How does cortex-M33, for example, know previous exception priority?

Hello I want to know about exception priority. In following situation A has highest priority, described as priority A. B has medium priority, described as priority B. C has lowest priority...
How does cortex-M33, for example, know previous exception priority?

Hello I want to know about exception priority. In following situation A has highest priority, described as priority A. B has medium priority, described as priority B. C has lowest priority...
MISSING FUNCTION PROTOTYPE AND REQUIRE ANSI-TYPE PROTOTYPE

COMPILE TIME ERROR::mini project.c(49): warning C206: 'lcddata': missing function-prototype ::mini project.c(49): error C267: 'lcddata': requires ANSI-style prototype PROGRAM #include<reg51.h...
MISSING FUNCTION PROTOTYPE AND REQUIRE ANSI-TYPE PROTOTYPE

COMPILE TIME ERROR::mini project.c(49): warning C206: 'lcddata': missing function-prototype ::mini project.c(49): error C267: 'lcddata': requires ANSI-style prototype PROGRAM #include<reg51.h...
Back down from uVision5 to previous version.

I have uninstalled uVision5, but I still get the link error for using an evaluation copy. How can I completely remove uVision5 and return to my previous working copy.