XOL-16 Redstone computer

A computer simple enough to build in Minecraft (hopefully) !

Project

• 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

Features

• 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)

Instruction Set ( wip )

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

rationale

nor + cpb are all the logic you'd need

proof:

not

cpb // b = a
nor // a = !(a | b) = !(a | a) = !a

or

nor // a = !(a | b)
#not

and

#not b ( not it before loading it into b)
#not a
nor // a = !(!a | !b) = !!a & !!b = a & b

implementing sub

ldc // load rhs
cpb
nor // not'ed rhs
cpb
ldc 0x01
add // done inversing rhs
cpb
ldc // load lhs
add

todo

• is a inversed version of jmp ( if a != 0 ) useful ?
• is cms/cmp redudant given we can == with xor ?

implem

• a_out/16
• d_out/8
• d_in/8
• read/write line
• request line
• reply line