The Ita computer system is a project I began in early 2010. I decided
that I would like to create a complete computer system on my own.
My goal was to create something reasonably "modern" (at least in my mind)
and strive to keep things as simple as possible/practical.
There are certainly different approaches one could take when creating
their own computer system. I decided to focus on the software and the
design of the hardware. However I decided not to try attempt physically
constructing the computer. Instead I have done VHDL designs for the
processors and then used an FPGA development board to test out the system.
All of the major hardware features for the project are complete. I
am now able to display bit-mapped graphics on the monitor. Unfortunately,
I have been running into many instabilities in the memory controller.
To get everything working with the bit-mapped grahics I am currently
running the CPU at 50MHz. In theory I should be able to run the CPU at 100MHz (or possibly
higher) once I can sort out these memory issues.
I am still hoping to boost the computers clock rate, and possibly
introduce a small cache for the CPU to improve performance.
This video shows a few graphical test programs written for the computer.
I have also implemented a mandelbrot generator to demonstrate the bitmapped
graphics capabilities of the system.
You can also try out the OS in your browser by using the JavaScript
simulator here.
Future Work
There are numerous areas of the computer system that I would like to
improve over time. The only real barriers are finding enough time and
motivation to complete them.
Hardware
The current CPU runs at 50MHz and uses a 50MHz memory bus. The memory
controller requires multiple cycles to read a single 32bit word over the
16bit data bus. I would like to increase the CPU and memory controller
performance by increasing the clock rate to 75MHz (in fact some parts of
the memory controller will have to operate a twice the clock rate).
I may also want to add a small L1 cache using the FPGA's on chip memory.
This should allow me to improve effective memory performance. I'll probably
aim for a simple combined instruction/data cache that is direct mapped
to keep things simple.
I am considering enhancing the graphics support by adding palettized
graphics. That would allow the computer to do some interesting
palette rotation effects. Another fairly simple feature would be to
add partial hardware support for filled vector graphics.
Software
Compiler
The current compiler does very little optimization of the generated code. In
order to improve the system's performance I would like to implement a
few simple compiler optimizations. For example the system should do
some constant folding optimizations. In general the compiler needs
to track constant values better so that unnecessary operations can
be eliminated, and so that fewer constants are stored on the stack
when they could be "immediate values" in the machine code without
ever existing on the stack.
Applications
I'd like to make some improvements to existing sample programs and
finish the text editor which is still a work in progress. As I add more
features to the system (e.g. bitmapped graphics) I plan on creating some
more applications to demonstrate the features.
