COMP4300 Lab 3 Solution

Lab Exercise Three
Objective
This lab develops some remaining datapath building blocks for the Aubie processor . It will be combined with the Aubie control logic to make a working cpu in Lab 4.
Instructions
Develop VHDL for the following components. You should define an architecture for each of the entities given below. You should test each entity by developing simulation files for the entity. Your architecture should implement the functionality described in the text for each entity.
You should use the types from the dlx_types and bv_arithmetic packages you used in lab2. The propagation delay through each unit should be 10 nanoseconds.

Register File. The register file consists of 32 registers numbered 0-31. In a given clock cycle one value can be read or one value can be written (not both). The propagation delay through the register file should be 10 nanoseconds for a read operation (zero for write, but write has no output). The reg_number is a five-bit number which specifies which register is being read or written. If a read is being done (readnotwrite is 1), the data_in input is ignored, and the value in register reg_number is copied to the data_out port. If a write is being done (readnotwrite is 0), the value present on data_in is copied into register number reg_number. The data_out port does not have a meaningful value for a write.

The entity declaration should look like:
entity reg_file is
port(data_in : in dlx_word; readnotwrite, clock: in bit; data_out: out dlx_word; reg_number : in register_index); end entity reg_file;


The entity should be implemented with an architecture consisting of a single VHDL process. You should use an array variable of 32 dlx_words to store the register values, something like

type reg_type is array (0 to 31) of dlx_word;
…
variable registers : reg_type;


32-bit single-value register. This will be used everywhere in the chip that a temporary value should be stored.

entity dlx_register is port(in_val: in dlx_word; clock: in bit; out_val: out dlx_word); end entity dlx_register;

The register should be sensitive to all inputs. If clock is one, the value present at in_val should be copied to out_val . When clock goes to zero, the output value is frozen until clock goes high again.


Deliverables
Please turn in the following things for this lab:
• A printout of your VHDL code.
• Your simulation test file. Do not exhaustively test these designs since they take lots of input bits, but do test a reasonable number of things.
• Transcripts/screenshots of tests running your simulations. You cannot test exhaustively, but you should demonstrate that all your modules work.
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