How to use the RISC-V and be able to turn it off and on

Hi there. I am trying to use the RISC-V core with a custom code to take a picture. In a separate project it is working with MBOX and communicating the image pointer in memory to the app core. Now I need to start the board, disable the RISC-V core, wait for a command, in this case using a UART command from the app core, awake the RISC-V core, run the code that takes the pic and communicate the pointer to the app core and be turned off. I tried to locate an example but not able to find something workable yet. Can you guide me to some guide or example?

Thanks in advance.

Luis

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