A Simple 8 bit Microprocessor
We present here a complete 8 bits microprocessor with all the tools needed
to build assembly program. This generic processor has been conceived and
realized from scratch in about two weeks. It was the first design we made,
so it was not optimal... but it worked !
We designed the microprocessor with the XACT software environment provided
by Xilinx. Then, we put it on a programmable Xilinx device. We used it with
an evaluation board containing a 32KB SRAM, a 6-digit hexadecimal display, a
16-key keyboard and the logic to establish a serial link with a PC.
The microprocessor could address up to 64K and drive all the peripherials
provided on the board. It was slow (0.3 MIPS), but it enabled us to make
some programs such as a stack-based decimal calculator, a maze game which
could transmit the map of the maze to a PC via the serial link, and a banner
to display a scrolling message.
The french report gives more information about the project.
* bdasm : the assembler we used to compile our programs.
* asm : a script to launch bdasm on asm .S files. We use cpp to preprocess
the asm sources.
* simu : the simulator. You may adjust its speed according to your
hardware. Try 'simu calc.bin' to launch the calculator. The 16-key
keyboard is emulated with the keys 0-9, a-f under X11.
* calc.bin : the calculator. It is stack based (RPN notation) and work
with 16 bits numbers.
keys : 0-9 : enter a number (modulo 2^16).
A : addition of the two number on the top of the stack. pop
them and put the result on the stack.
B : substraction.
D : enter the current number on the stack.
E : drop a number from the stack.
F : clear the current entry of the stack.
C : shift key. Then Press on :
A : multiplication
B : division ( 16 bits / 8 bits)
C : copyright notice :-)
example : 1 2 3 D
D F 4
to calculate : (123+5)*4
* banner.bin : a simple banner. You should adjust the speed on the
simulator to read it well.
* laby.bin : a maze game - read the sources to understand :)
* xxx.S : the assembler sources for all the programs
* doc/ : the report (in French)
* scheme/ : the complete schemes of the microprocessor in postscript, and
the logic functions in ascii.
* All these tools are provided 'as is'.
* The tools have been compiled under Linux. They should work on any Unix
computer with X11.
Fabrice Bellard & Sylvain Delas.