Skip to content

Latest commit

 

History

History
142 lines (92 loc) · 3.77 KB

getting-started.md

File metadata and controls

142 lines (92 loc) · 3.77 KB
Raw

Getting started with cdm-devkit

Some tips to start developing for CdM processors with cdm-devkit

Installation

  • Install cdm-devkit

  • Make sure you have cocas available in your terminal, otherwise add your (PYTHON_DIR)/Scripts to PATH

    (PYTHON_DIR is your Python istallation folder)

Writing a program

You can write your assembly programs in VS Code:

  • Create a folder and open it with VS Code

  • Create a file with .asm extension

  • Write your program

  • Assemble your program with cocas

    cocas -t <target> <file>

    <target> - processor name (list available names with cocas -T)

    <file> - file to be assembled

  • You get an output file with .img extension that you can upload to Logisim

Code templates

CdM-8/8e

asect 0
# Your program starts from 0x00 address

start:
    # your code here

end.

CdM-16

asect 0
main: ext               # Declare labels
default_handler: ext    # as external

# Interrupt vector table (IVT)
# Place a vector to program start and
# map all internal exceptions to default_handler
dc main, 0              # Startup/Reset vector
dc default_handler, 0   # Unaligned SP
dc default_handler, 0   # Unaligned PC
dc default_handler, 0   # Invalid instruction
dc default_handler, 0   # Division by zero
align 0x80              # Reserve space for the rest 
                        # of IVT

# Exception handlers section
rsect exc_handlers

# This handler halts processor
default_handler>
    halt

# Main program section
rsect main

main>
    # your code here

end.

Getting started with Logisim

Logisim is a program that is used to simulate logical schemes.

You can download it here

  • Open Logisim

  • Load desired processor

    • Project > Load Library > Logisim Library
    • Select desired .circ processor scheme (you can find one in cdm-devkit-misc archive)
    • Now you have new category with a processor name in Logisim's left menu
    • Get processor from this category and put it on your canvas

  • Build your scheme

  • Load assembled program (.img file) to your program memory

    • Right-click on memory chip and select Load Image
    • Select .img file (one that you got from cocas)

    In Harvard architecture, where you have separate memory chips for ROM and RAM, you need to load image to ROM chip

  • Run the simulation with Simulate menu

    Useful keyboard shortcuts:

    • Ctrl + K - toggle clock
    • Ctrl + R - reset simulation
    • Ctrl + E - toggle simulation

Scheme templates

CdM-8/8e

Processor symbols may differ, but inputs and outputs are the same

CdM-8/8e in Von Neumann configuration:

cdm8-vn


CdM-8/8e in Harvard configuration:

cdm8-hv

Here instr memory aka instruction memory is ROM and data memory is RAM

CdM-16

With CdM-16 you should use special memory chips:

  • In Logisim go to Project > Load Library > JAR Library

  • Select logisim-banked-memory-*.*.*.jar that is located in cdm-devkit-misc archive in jar folder

  • Now you have new category in Logisim's left menu that is called BankedROM&RAM

  • You should use ROM and RAM from this category

These chips emulate real banked memory configurations and allow processor to read and write 2 bytes per bus cycle

CdM-16 in Von Neumann configuration:

cdm16-vn

Memory chip is RAM from logisim-banked-memory

Harvard configuration is build the same way as with CdM-8/8e, but with memory from logisim-banked-memory. In this case word should be connected to both RAM and ROM