a simple problem in VHDL

[Behi Jon]

Hi,
I have to write a simple code for this circuit :

we have eight registers(each one: 8-bit) and two mux(8-1), and each mux, must select one of these eight registers and this two selects will be the input of an ALU.
Then ALU has to perform an operation according to its opcode and produce a result and this result goes to one of eight registers(by a decoder) .

How can I do all these ? These operations must execute sequentially and I can't use a process for them. And concurrent code won't work.

I don't want code, just a little help.
First, the code related to muxes must execute and then code of ALU and then storing result in registers. How can I prevent executing concurrently ?

thanks..............