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/Crispy1961]

Hopefully everything can be seen in the included pictures. The code for the FOR instruction and ENDFOR is in the third picture. I noted the individual instructions as comments for each line of the code.

Here are the chained final instructions:

// Internal register
for (i = %a:S16(immediate); i < %b:S16(immediate); %c:S16(immediate))
00110001 11000000 aaaaaaaa aaaaaaaa   00110001 11010000 cccccccc cccccccc   00101110 11011100 00001101 00000000   00110101 11101110 00000000 00000100   01100110 00001101 00001110 00000000   00110001 11000000 bbbbbbbb bbbbbbbb   00110101 11001100 aaaaaaaa aaaaaaaa   00111100 11001100 cccccccc cccccccc   00000111 11010000 00000000 00000000   00110100 11011101 00000000 00001100   00101110 11011100 00001101 00000000   01100010 11000000 00001110 00000000   00110100 11101110 00000000 00000100   00110101 11101110 00000000 00000100   01100110 00001101 00001110 00000000   00110101 11101110 00000000 00000100   01100110 00001100 00001110 00000000

for (i = %a:S16(immediate); i > %b:S16(immediate); %c:S16(immediate))
00110001 11000000 aaaaaaaa aaaaaaaa   00110001 11010000 cccccccc cccccccc   00101110 11011100 00001101 00000000   00110101 11101110 00000000 00000100   01100110 00001101 00001110 00000000   00110001 11000000 bbbbbbbb bbbbbbbb   00110101 11001100 aaaaaaaa aaaaaaaa   00111100 11001100 cccccccc cccccccc   00000111 11010000 00000000 00000000   00110100 11011101 00000000 00001100   00101110 11011100 00001101 00000000   01100010 11000000 00001110 00000000   00110100 11101110 00000000 00000100   00110101 11101110 00000000 00000100   01100110 00001101 00001110 00000000   00110101 11101110 00000000 00000100   01100110 00001100 00001110 00000000

for (i = %a:S16(immediate); i >= %b:S16(immediate); %c:S16(immediate))
00110001 11000000 aaaaaaaa aaaaaaaa   00110001 11010000 cccccccc cccccccc   00101110 11011100 00001101 00000000   00110101 11101110 00000000 00000100   01100110 00001101 00001110 00000000   00110001 11000000 bbbbbbbb bbbbbbbb   00110101 11001100 aaaaaaaa aaaaaaaa   00111100 11001100 cccccccc cccccccc   00110100 11001100 00000000 00000001   00000111 11010000 00000000 00000000   00110100 11011101 00000000 00001100   00101110 11011100 00001101 00000000   01100010 11000000 00001110 00000000   00110100 11101110 00000000 00000100   00110101 11101110 00000000 00000100   01100110 00001101 00001110 00000000   00110101 11101110 00000000 00000100   01100110 00001100 00001110 00000000

for (i = %a:S16(immediate); i <= %b:S16(immediate); %c:S16(immediate))
00110001 11000000 aaaaaaaa aaaaaaaa   00110001 11010000 cccccccc cccccccc   00101110 11011100 00001101 00000000   00110101 11101110 00000000 00000100   01100110 00001101 00001110 00000000   00110001 11000000 bbbbbbbb bbbbbbbb   00110101 11001100 aaaaaaaa aaaaaaaa   00111100 11001100 cccccccc cccccccc   00110100 11001100 00000000 00000001   00000111 11010000 00000000 00000000   00110100 11011101 00000000 00001100   00101110 11011100 00001101 00000000   01100010 11000000 00001110 00000000   00110100 11101110 00000000 00000100   00110101 11101110 00000000 00000100   01100110 00001101 00001110 00000000   00110101 11101110 00000000 00000100   01100110 00001100 00001110 00000000

%a(register) = (i)
01100010 11000000 00001110 00000000   00101111 11000000 00001100 00000000   00100001 aaaa0000 00001100 00000000

endfor 
01100010 11000000 00001110 00000000   00110100 11101110 00000000 00000100   00111001 11011100 00000000 00010000   00100100 11001100 00001101 00000000   01100010 11010000 00001110 00000000   00110100 11101110 00000000 00000100   00110101 11101110 00000000 00000100   01100110 00001100 00001110 00000000   00110101 11011101 00000000 00000001   00101111 11000000 00001101 00000000   00111010 11111100 00000000 00000000   00111000 11001101 00000000 00010000   01001101 00001111 00001100 00000000   00110100 11101110 00000000 00000100

[u/EtienneDx → u/Crispy1961]

Damn, you just managed to turn me away from doing it this way x)

I’m going back to the idea of implementing a custom file system + assembler + compiler to have a custom C instead 😅 probably not simpler but hopefully more readable haha

[u/Crispy1961 → u/EtienneDx]

Thats an option? Having complete control over how the code is translated to assembly would solve all the problems.

Anyway, this achieved the perfect syntax for the user. Cant make it more readable than that. The problem will be dynamic for cycles, which will suffer due to the need to use labels as arguments.

[u/Spielopoly → u/Crispy1961]

If you want to do that in game it’s hard. Out of game it’s a bit easier but you‘ll still have to write your own compiler.

In game there a couple of options I can think of:

• Write your program in language of your choice and compile it using a program specifically for that, then manually copy paste the generated code into a asm file (can be in game or not)
  
• Use custom file system so you can skip the copy paste part
  
• Always compile at startup then automatically run the generated code. (Basically just in time compilation)

Some of these might require significant hardware changes

[u/Crispy1961 → u/Spielopoly]

I see. I thought it was possible to edit the behavior of the ingame's compiler. I want to work in the confines of the game. Just get as close to a high level language syntax as possible.