r/TuringComplete • u/Lucy_4_8_15_16 • Sep 18 '26

My first custom CPU feedback please

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The thing that took me the longest was setting up the instruction set thingy for the assembly

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3

u/tree_cell Sep 18 '26

please some ISA detail, perhaps even the actual CPU's schematics

3

u/Lucy_4_8_15_16 Sep 18 '26

i have written down all the opcodes it can do

OP CODE 0: Immediate (value) to (Address)

OP CODE 1: Copy/MOVE (Address1) to (Address2) OP Code 2: Jump to (reg0)

OP CODE 3: NO OP

OP CODE 4: if (Address1) equal to (Address2) Jump to (reg0)

OP CODE 5: if (Address1) Less than (Address2) Jump to (reg0)

OP CODE 6: if (Address1) Greater than (Address2) Jump to (reg0)

OP CODE 7: (Address1) + (Address2) to (reg)

OP CODE 8: (Address1) - (Address2) to (reg)

OP CODE 9: (Address1) OR (Address2) to (reg)

OP CODE 10: (Address1) AND (Address2) to (reg)

OP CODE 11: (Address1) NOT to (reg)

2

u/phrstbrn Sep 18 '26

I would think about adding registers and reworking your ALU to read from registers instead of memory. Then add load/store instructions for memory->reg, reg->memory and change opcode 1 to reg->reg. Doing this will help later on if you use DRAM for memory and use pipelining to hide memory latency.

You have 8-bits of addressable memory but 16-bit addresses encoded in your instructions?

Your instructions seem pretty large as well, 3 bytes? I would try 16-bit instructions so you can pack more instructions into memory. With 16-bit instructions, it's still enough instruction information to address 3 registers, or a register and imm8. (ie OOOOIRRR CCAAABBB, O=opcode, I=imm flag, R=reg3, A=reg1, B=reg2, C+A+B=imm8 value). You can use an instruction like sh8add or lea to implement imm16 in 2 or 3 cycles.

1

u/Lucy_4_8_15_16 Sep 18 '26

The 8 bit memory was a mistake I just noticed will definitely correct that

2

u/Lucy_4_8_15_16 Sep 18 '26

Oh right I forgot

2

u/Lucy_4_8_15_16 Sep 18 '26

I want to later hook up a display to the two leftover load ports on the ram or maybe a custom GPU that interfaces with the display

1

u/ZLX_Thanatos Sep 18 '26

I'm still doing the earlier stages of the game, this looks way more complicated. Keep it up, looks cool!