Sub Fastcall behaviour - Printable Version

Sub Fastcall behaviour - Printable Version

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Sub Fastcall behaviour - na_th_an - 07-27-2012

I understand that if, for example, you pass an uByte parameter, it's put into the A register... But it seems that the parameter itself is not usable from BASIC. I don't know if this is intended, there's nothing about this in the doc.

Code:
Sub Fastcall test (n as uByte)

    Asm

        ld (40000),a

    End Asm

    Print n

        Print Peek (40000)

End Sub

test (16)

I expected this code to print 16 twice, but it outputs:

Code:
0

16

This is, the value of "n" is 0. In other scenarios, I get other values, not just 0.

Re: Sub Fastcall behaviour - boriel - 07-27-2012

This is not possible.
FASTCALL is used for registers. I could manage to use the A register for "N var", but the content will be lost.
FASCTALL is used for ASM functions basically, or for SUB/Functions with no parameters.

In the future, functions with no parameters will be all fast-called.

Re: Sub Fastcall behaviour - na_th_an - 07-30-2012

Nice to know. It would be nice to mention this in the docs, as it is not, and may mislead people (i.e. me :lol Smile

Re: Sub Fastcall behaviour - boriel - 07-30-2012

na_th_an Wrote:Nice to know. It would be nice to mention this in the docs, as it is not, and may mislead people (i.e. me :lol

It would be nice to use only registers, but Z80 has so few registers, I couldn't manage to do it. :oops:

Re: Sub Fastcall behaviour - na_th_an - 07-30-2012

No, it's incredibly useful. What I meant is that the behaviour "you can't really use the variables" should be documented. I mean, if the fastcall sub has a byte parameter "X", that parameter goes into the A register, but that's it, there's no "X" local variable you can use. Well, there is, but the value is not.

Re: Sub Fastcall behaviour - boriel - 07-30-2012

na_th_an Wrote:No, it's incredibly useful. What I meant is that the behaviour "you can't really use the variables" should be documented. I mean, if the fastcall sub has a byte parameter "X", that parameter goes into the A register, but that's it, there's no "X" local variable you can use. Well, there is, but the value is not.

Hmmm. Maybe the compiler can issue a Warning like "Warning: Fastcalled var is not accesible" :?:

Re: Sub Fastcall behaviour - na_th_an - 08-02-2012

boriel Wrote:
na_th_an Wrote:No, it's incredibly useful. What I meant is that the behaviour "you can't really use the variables" should be documented. I mean, if the fastcall sub has a byte parameter "X", that parameter goes into the A register, but that's it, there's no "X" local variable you can use. Well, there is, but the value is not.
Hmmm. Maybe the compiler can issue a Warning like "Warning: Fastcalled var is not accesible" :?:

It would be useful, but just mentioning it in the wiki (that's the docs I always read) would suffice. The wiki explains how to use the fastcall parameters and stuff, but doesn't mention this issue.