My CPU

Now let us take a look at how the functional CPU (FunCPU for short) can be programmed in reality, from the programmer’s point of view.   This will be covered by looking at each gizmo  (i.e. button, switch, LED, etc.) on the front/control panel. On the bottom right side, the purpose of the…

It is not trivial how to handle argument passing in the lack of stack, or any dedicated storage for parameters. Consider the following examples: fac (n):= n*fac(n-1) fac(add(2,3))? ack(add(fac(fac(2)+fac(1)),fac(1)),1)? I wanted a simple solution, which still works without posing serious…

When evaluating expressions, the CPU must exactly know how to evaluate an expression, what function/expression parts should be evaluated first, next, and last etc. Therefore the representation of expressions and functions must be unambigous with respect to parenthesis and priorities. In…

It is not trivial how expressions should be reduced, i.e. evaluated. I have already mentioned that while some strategy could be fruitful in reducing an expression in a given interpretation, others may be not. Let us have a look at the following simple example of evaluation of the factorial function…

Needless to say that not only initial and final expression, but also temporary expressions should be stored in memory somehow. The way of how expressions are represented has impact on hardware design. During reduction the cycles, expression symbols are being copied one by one. When a function…

In the previous post we have seen how 8 bit symbols represent literals, arguments, functions, etc. Similarly, it was vital to have a good and efficient function encoding. Basically in the context of function encoding we need to be able to answer the following question: Where does the function…

In the memory, different type of symbols are stored together. It is essential for the CPU to be able to differentiate among them. Therefore type information is required to be assigned to each unit of information. This piece of information is tagged to each symbol. A lot of effort has been dedicated…

As the computational model will be purely functional without any imperative elements (which could introduce side effects), a simple expression rewriting system will be adequate. User-defined functions will make up a library, which will in turn, also define the rewriting rules. Functions from…

FunCPU will operate with 7-bit numerals (to understand why see the next couple of posts) and will directly support the following built-in functions: inc(x) is used for incrementing a value, that is for any x: x+1=inc(x). dec(x) is used for decrementing a value in the similar fashion. if-then-else…

It has been a long time since my last CPU project, which focused on a very simple 8 bit CPU. Nothing groundbreaking, just a very simple variation of an accumulator machine.  This time I have set out a different, more ambitious goal. I have wanted to create still something simple, but…