sub and function, asm and ix

[nitrofurano]

when advancing a bit more on the MSX part of Boriel's ZX-Basic Compiler, and after that help from accessing paged memory on ZX-Spectrum 128k, i got this situation:

the library i used on the MSX "version"

Code:

sub msxvpoke(tad as uinteger,tva as uinteger) asm ld h,(ix+5) ld l,(ix+4) ld a,(ix+6) call $004D end asm end sub

there i'm seeing that sub is using 'ix' from the arguments, but i don't know how are they arranged (as ubyte, uinteger, etc.), and why or what for we use fastcall, get ix instead of bc,de,hl,af - and from a function, in which register or index the value is returned (af, just like from fastcall?)

i can't find documentation explaining it better on the wiki: <!-- m --><a class="postlink" href="http://www.boriel.com/wiki/en/index.php/ZX_BASIC:FUNCTION">http://www.boriel.com/wiki/en/index.php ... C:FUNCTION</a><!-- m --> and <!-- m --><a class="postlink" href="http://www.boriel.com/wiki/en/index.php/ZX_BASIC:SUB">http://www.boriel.com/wiki/en/index.php/ZX_BASIC:SUB</a><!-- m -->

thanks and cheers!