Rhombus

a stack-less PDP-11-ish virtual machine inspired by ARM and RISCV.

instructions

instruction type	argument type	argument type
no argument	-	-
label	@label	-
register	register	-
memory	[memroy]	-
index	#label[index]
register-register	register	register
value-register	$value	register
index-register	#label[index]	register
register-memory	register	[memory]

control flow

instruction	description
mov src, dest	copies data from source to destination
cmp src, dest	compares source to destination
jmp dest	jumps to program instruction
jmpe dest	jumps to program instruction if result of the last instruction was zero = true
jmpb dest	jumps to program instruction if result of the last instruction was zero = false and negative = overflow
jmps dest	jumps to program instruction if result of the last instruction was negative != overflow

arithmetic

instruction	description
add src, dest	addition
sub src, dest	subtraction
shr src, dest	shift right
shl src, dest	shift left
xor src, dest	xor
or src, dest	or
and src, dest	and

input and output

instruction	description
print src	print register to IO
scan dest	scan from IO to register

data

instruction	description
db data	this instruction gives a pointer relative to program's beginning for using later

flags

flag	description
negative	if result of the last operation was negative, set to true
zero	if result of the last operation was zero, set to true
overflow	if result of the last operation caused signed overflow, set to true
carry	if result of the last operation caused unsigned overflow, set to true

memory

the machine has 64KB of fixed-size memory that you have direct access. your program is separate and doesn't take anything from it.

registers

purposes are just convention and are not enforced. but be wary of overwriting the instruction pointer or i0

register	purpose
i0	instruction pointer
i1	return address
i2	function argument
i3	function argument
i4	function argument
i5	function argument
i6	function argument
i7	function argument
i8	function argument
i9	general purpose
i10	general purpose
i11	general purpose
i12	general purpose
i13	general purpose
i14	general purpose
i15	general purpose

Examples

hello world

; examples/hello_world.rhom
@STR
    db "HELLO, WORLD!"
    
@PRINT_LOOP
    print #STR[i9]
    add $1, i9
    cmp $13, i9
    jmps @PRINT_LOOP

basic repeater

; examples/repeater.rhom
@BEGINNING
    scan i9
    print i9
    jmp @BEGINNING