A node X can use all 64 words of a neighbor node R0 as RAM.
Assuming X's b register points to R0, and R0 is executing from port X, this is how node X reads word at addr from node R0:
: ramread ( addr -- v )
@p !b !b
@p a! @ !p
@b ;
it works by sending a tiny four-opcode program @p a! @ !p to node R0. R0 executes this program:
- @p asks X for another word
- a! stores the word in R0's a register
- @ fetches from R0's RAM at address a
- !p writes the result back to the caller, in this case node X.
After node X has sent this program to R0, it reads the result back from R0.
Writing to R0 can be done in a couple of ways. To write a value v to the same location as was just read, X can do:
: ramwrite ( v -- )
@p !b !b ;
@p ! . .
The trick here is that R0's a already points to the correct word, because of the preceding ramread.
The above are good factors for a read/modify/write, for example to negate a word in RAM:
call ramread - call ramwrite