Stack space

Lucky

If the method your launching into a new cog is spin, the cognew command requires a stack pointer, but if its assembly code it doesn't? Why doesn't assembly routines need a stack pointer?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"The man who smiles when things go wrong has thought of someone to blame it on."


-Lucky[size=-1][/size]

jazzed

PASM does not use a stack. Subroutines in PASM are called using the jmpret instruction.
The second parameter for cognew with PASM is the value given to the new COG's PAR register.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
May the road rise to meet you; may the sun shine on your back.
May you create something useful, even if it's just a hack.

pullmoll

Lucky said...
If the method your launching into a new cog is spin, the cognew command requires a stack pointer, but if its assembly code it doesn't? Why doesn't assembly routines need a stack pointer?

Because in PASM there is no stack pointer and thus no need for a stack. Calls to subroutines are executed by modifying the accompanying return instruction, which is why recursion isn't possible in PASM without additional measures, e.g. creating a stack in hub RAM.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
He died at the console of hunger and thirst.
Next day he was buried. Face down, nine edge first.

MagIO2

The call is only a compiler-instruction. If you have a "call #somewhere" instruction, the compiler searches for a "somewhere_ret" label. There you have to put the ret instruction. When the call is executed, the current program counter + 1 is stored in the source-field of the ret instruction.

There are 2 lessons to learn:
1. You can't have multiple ret instructions in a subroutine as only the one behind the x_ret label will relly return then.
For example:
call #doSomething
...
doSomething
' check condition
...
IF_C ret
' if not C do something
...
doSomething_ret
ret

This would not work as desired. If you want to exit the subroutine before, you have to jump to the _ret

2. call is self-modifying code. So you should not have empty subroutines as placeholder during development:

' the main code already calls an empty subroutine
call #doSomething
....

doSomething
doSomething_ret
ret

A self-modified instruction can't be executed as next instruction, as the unmodified version is already loaded into the execution pipeline. So, you'd have to put a NOP in between doSomething and doSomething_ret.