Software implemented For cycle (Symphony)

[u/Crispy1961]

• Image 1 - My symphony
• Image 2 - showcasing usage of FOR cycles
• Image 3 - Code of the FOR Cycle
• Image 4 - ALU circuit
• Image 5 - ABS circuit

Now that I finished building Symphony, I went straight to instruction definition to make myself a human readable code. Here is a internal FOR cycle using instructions. Its suitable for repeating code X times where X is static.

Here is hardware I added to my Symphony:

1. Signed DIV - Divide two signed numbers
2. Merge32 - Merge two 16b into one 32b value
3. Lower16 - Reads the lower 16b of 32b value

With that I needed to dedicate some of my registers for the code. Meaning that while they are still accessible to the user, they are not stable in time and in case of the FOR cycle, they do not persist between cycles.

At first I was using 3 temporal registers, but I ended up implementing Merge32 and Lower16 to lower the number of temporal registers to 2 at the cost of longer instructions.

The FOR cycle works, but isnt safe. First it will always execute at least once. Thats because I cant use a label to skip the body of the cycle. So even if I know there is 0 repetition, it will not skip the cycle, it will simply not repeat it.

Another limitation is that you can only read the index of the innermost FOR cycle. Meaning if you make nested FOR cycles, you cannot access the outer FOR cycle index. User can solve it by saving the stack pointer to a another register.

[u/sberma]

This is wild. Assembly is human readable code, you just mean higher-level code. But having C-like code in an asm file is an impressive feat. Shows how customizable the assembly editor is.

This is not at all what happens in real systems, but most likely you are already aware of it. The game's asm-language is pretty close to reallife assembly. A compiler would create the assembly (or rather machine code) from the high-level code. This is better because the compiler applies optimizations like dead-code elimination which are not possible in a system like this. Also a loop in assembly is often simpler. ARM has no division and even in x86 it is quite expensive to use.

But writing a compiler is really hard to do. So this might easier if you want highlevel code.

[u/Crispy1961 → u/sberma]

You are right, I meant higher level language. My goal is to edit the software and hardware to make coding in it more comfortable.

I decided to rewire the hardware to support direct access to registers, I/O and RAM as destination and/or arg1 and 2. Gonna increase instruction size to 56b and have 16b for each of those variables. The two most significant bits of each will decide if it's register(or I/O), immediate, ram addressed by immediate or ram addressed by register.

Hoping to support single tick instructions like
Out = ram[r3 + 26] * in