CompactRISC16 (CR16) CPU

This is an implementation of the CompactRISC (CR16) CPU written in Verilog and SystemVerilog with an assembler written in Java for the Computer Design Laboratory ECE 3710 class at The University of Utah. This CPU was designed to run on an FPGA and interface with peripheral components and hardware. Our group’s final project for this class is entitled “FSS Prototype” and uses this CPU and assembler. More information on our final project can be found here.

Authors

• Jacob Peterson
• Brady Hartog
• Isabella Gilman
• Nate Hansen

How This Repository is Organized

• .formatter/verilog/ contains the Verilog source code formatter. More info on it here.
• assembler/ contains the source code for our custom assembler written in Java. More info on it here.
• docs/ contains the following: LaTeX source files and compiled PDFs of our lab reports for this class, various datasheets and documentation (including our custom CR16 ISA), and class handout of a CR16 block diagram guideline.
• resources/bram_init/ contains block RAM (BRAM) initialization files encoded in UTF-8 hexadecimal characters.
• resources/pin_assignments/ contains exported CSVs of pin assignments for the various Verilog top modules in this repository.
• src/asm/ contains assembly source code files written in accordance with our custom ISA which can then be assembled with our custom assembler.
• src/v/rtl/ contains the Verilog and SystemVerilog RTL code for our custom CR16 processor. Note that it contains various top-level modules that were used to test certain RTL modules during our development process. The main cr16.sv module source code is located here.
• src/v/tb/ contains the Verilog and SystemVerilog testbench code for testing the various CR16 processor modules.

Assembler

To compile an assembly code file in accordance with the CR16 ISA, run the assembler/assembler shell script with the given arguments as outlined below. Some example programs are given in src/asm. A good example showing the capabilities of the ISA and the assembler is shown in src/asm/test_all/all.asm. Note that the Java Runtime Environment is required to run the assembler and must be of version 11 or greater. Also note that you may need to make the script executable via: chmod 755 assembler/assembler.

Usage: assembler [options] <assembly code file path>
  Options:
    -d, --debug
      Turns on debug mode.
      Default: false
    -p, --max-padding-line
      The line number to which padding lines should be added to an output
      binary.
      Default: 0
    -v, --max-padding-line-value
      The decimal value of the padding lines.
      Default: 0
    -b, --number-base
      The number base of the output binary.
      Default: HEX
      Possible Values: [BINARY, DECIMAL, HEX]
    -o, --output
      The output binary file path. Defaults to <input assembly file>.dat.
    -s, --output-processed
      True to write the processed assembly to <output binary file
      path>.processed.asm.
      Default: false

Verilog Source Naming Conventions and Format For This Repository

• File names, module names, and wire/reg assignment names should be snake case (e.g. my_verilog_module.v)
• Testbench modules and file names should be appended with a _tb (e.g. my_verilog_module_tb.v)
• Top level modules and file names should be appended with a _top (e.g. my_verilog_module_top.v)
• There should only be one module per source code file
• Module instantiations should use uppercase named port lists with inputs prepended with I_ and outputs prepended with O_ (e.g. my_verilog_module(.I_INPUT_1(my_input_1), .O_OUTPUT_1(my_output_1));)
• Module signatures and bodies should use parameters instead of hard-coding constants. When defining the parameters for a module instantiation or for a module signature, the parameter list should start on the next line, but if there is only one parameter, it should be defined on the same line as the module instantiation or signature (same goes for the port list of a module).
• The port list in module signatures should contain input and output port direction declarations, as opposed to those port direction declarations being placed in the body of the module.
• Consecutive single line comments should always be aligned with eachother if there are no lines between them.
• If there are 2 or more consecutive lines (including no comments between the consecutive lines) that assign a parameter, localparam, wire, or reg to a constant or to a single-line expression, then the equals signs in those lines should be aligned.
• If a single-line expression/assignment needs to be split into multiple lines, then the following lines should be further indented by 8 spaces, or if the subsequent lines can fit within the 100 character column limit, then the subsequent lines should be further indented until they are aligned to the expression/assigment on the first line.
• No line should be greater than 100 characters.
• Use non-blocking assignments (e.g. <=) in sequential @always blocks and blocking assignments (e.g. =) in combinational @always blocks.
  • An @always block is sequential if it is sensitive to the posedge or negedge of an input signal, whereas it is combinational if it is sensitive to signals without the posedge or negedge modifier included in the sensitivity list.
• Module sections should generally follow the following format, from top of file to bottom of file:
  • Module signature with parameter list, then input wires, then output reg/wires
  • localparams that defines constants for the rest of the module
  • Internal register and wire declarations
    • Prepend reg/wire names with q_ to represent a ‘current state’ register/wire and n_ to represent a ‘next state’ register/wire
  • Output mapping assign statements which map internal wires/registers with module output wires/registers
  • RTL logic with assign statements for all internal wires which generally consist of ternary operators
  • Module instantiations using named port lists in the instantiation signature and a module instance name that is the same as the module name (or a name that’s more concise and applicable to the instantiation), but with i prepended
  • Clock @always blocks which generally should only include posedge I_CLK in the sensitivty list
  • Other @always (such as internal finite state machines) or task blocks

Verilog Source Formatting For This Repository

To format verilog source code, use the istyle-verilog-formatter tool via the format script:

.formatter/verilog/format <paths to files or directories>

For example, to recursively format Verilog source files in the src directory, use the following command:

.formatter/verilog/format src

The istyle-verilog-formatter is used as a submodule in the .formatter/verilog directory. Either clone this repository with git clone --recurse-submodules or use git submodule init; git submodule update to clone the istyle-verilog-formatter repository into the .formatter/verilog directory so that the format script can run properly. The format shell script will run make if the iStyle binary is not already present in the istyle-verilog-formatter directory. Note: you may need to make the script executable via: chmod 755 .formatter/verilog/format.