Q: If there are two operations, such as CPU write and CLA read, to the same variable in the CPU to CLA message RAM, which one will be firstly to be executed? And after this operation, will the left one to be done immediately, or to be ignored?

A: Both accesses will be serviced, highest priority first.  The arbitration is described in the appendix of the CLA Ref Guide.  This also applies to different variables within the same message RAM. http://www.ti.com/lit/spruge6