About the start address and length of "_DATA_GROUP_"

In my project without OS, there are two task, one is Encryption Task, another is Seirial_ISR Task.

Strictly speaking, the above is self-contradictory. If you have no OS, you don't have tasks to speak of. And this assumption

when entering Serial_ISR it must save the sapce that Encryption Task used.

is pretty much guaranteed to be wrong. Not only would it be terribly much work to do that, it would achieve nothing useful. You would waste a lot more time copying all those data around than it could possibly cost to have the ISR (or the rest program) just use that memory you want to use as an intermediate holding area.

To put it bluntly: you're going at this in entirely the wrong way.

In my project without OS, there are two task, one is Encryption Task, another is Seirial_ISR Task.

Strictly speaking, the above is self-contradictory. If you have no OS, you don't have tasks to speak of. And this assumption

when entering Serial_ISR it must save the sapce that Encryption Task used.

is pretty much guaranteed to be wrong. Not only would it be terribly much work to do that, it would achieve nothing useful. You would waste a lot more time copying all those data around than it could possibly cost to have the ISR (or the rest program) just use that memory you want to use as an intermediate holding area.

To put it bluntly: you're going at this in entirely the wrong way.