A computer simple enough to build in Minecraft (hopefully) !
- Simple enough that I can finish it without losing interest
- Can run interesting stuff
- Write a simple assembler/mayyybe retarget a C compiler ?
- Flex on the freshman kids who struggle with their CPU class :D
- 16-bit address bus
- 8-bit data bus
- Add and Nor. No sub, no other bitwise ops.
- Absolute branching
- One(!) addressing mode via a dedicated register (+ immediate loads)
Registers:
- A: Accumulator, 8b
- B: O
🅱️ erand, 8b - C: Condition, boolean
- D: Delta, 16b: For branching
| mnemonic | effects | commentary |
|---|---|---|
| add | a = a + b, c = overflow | vanilla normal addition |
| nor | a = !(a | b) | complete singleton logic operand |
| cpb | b = a | Copies a into b |
| cmp | c = a == b | compare a and b |
| cms | c = a < b | strict comparison |
| jmp | pc = d | Inconditional jump |
| jmc | if(c == true) pc = d | Conditional jump |
| cpl | d[7..0] = a | Copy A to lower 8 bits of delta register |
| cph | d[15..8] = a | Copy A to upper 8 bits of delta register |
| ldc | a = *(pc++) | Load from constant |
| get | a = *d | Load from address |
| put | *d = a | Store to address |
| psh | push(a) | Push A contents to stack |
| pek | a = peek() | Read the contents of the top of the stack and puts it into A |
| pop | a = pop() | Pop stack and reads it's contents in A |
| out | print(a) | Sends the content of A to the standard output |
proof:
cpb // b = a
nor // a = !(a | b) = !(a | a) = !a
nor // a = !(a | b)
#not
#not b ( not it before loading it into b)
#not a
nor // a = !(!a | !b) = !!a & !!b = a & b
ldc // load rhs
cpb
nor // not'ed rhs
cpb
ldc 0x01
add // done inversing rhs
cpb
ldc // load lhs
add
- is a inversed version of jmp ( if a != 0 ) useful ?
- is cms/cmp redudant given we can == with xor ?
- a_out/16
- d_out/8
- d_in/8
- read/write line
- request line
- reply line