clarify stack arguments

README.md

@@ -20,16 +20,22 @@ If you are intersted in contributing have a look at [[CONTRIBUTING.md]]
 | n.a. | zr |
 | preserved | sp, r8 - r12 |
 | scratch | flags, r1 - r7 |
-| arguments | r1 - r5, r6 = stack args, r7 = stack res |
-| result | r1 = low word, r2 = high word |
+| arguments | r1 - r7 |
+| result | r1-r7 |
 | return address | r13 |
 
-### Stack
-grows downwards from top of memory
-arguments are passed in reverse order with the stack so:
+Arguments not fitting into the 7 registers should be passed on the top of the stack, meaning they should be the last values pushed before the function call.
+Arguments are passed in reverse order with the stack so:
 lowest address = 1st stack arg
 highest address = last stack arg
 
+Should a function return more values than fit into the 7 registers, the caller has to allocate space on the stack for them, and pass the pointer to that space in r7.
+This reduces the amount of argument registers to 6 and all arguments above that shall go on the stack, the pointer to the result stack shall **always** be passed in r7.
+r7 points at the highest available address for results, with the 8th result being stored there, the 9th below it and so on.
+
+### Stack
+Grows downwards from top of memory.
+
 ### Types
 
 #### String