flat assembler
Message board for the users of flat assembler.

Index > Non-x86 architectures > how to realize CPU adresses words not bytes

Author
Thread Post new topic Reply to topic
ProMiNick



Joined: 24 Mar 2012
Posts: 688
Location: Russian Federation, Sochi
ProMiNick
hello.
lets suppose that for custom CPU memory addressed not by bytes but by words - how to make proper labeling (all instructions are word sized, all data are words or word sequences).
of corse we could walkaround of that & encode all instructions with address operand divided by 2.
but how to make that at least org, virtual, $, $$ will operate on memory addressed by words not bytes?
for example something like this
Code:
address :       encoded as              mnemonic
00000000:                               org 0
00000000:       03 03                   jmp hello
00000001:       03 65                   jmp hello2-2
00000002:       03 08                   jmp hello+5
00000003:                               hello:
00000004:                               org $30
00000030:       03 20                   jmp $20
00000031:                               virtual at $+51
00000064:       ?? ?? ?? ?? ?? ??       rw n
00000067:                               hello2:
00000067:                               end virtual
00000031:                               n=($-$$)*3    

there 2 solutions come in my mind:
1) initialy place source in virtual block & for each stored block produce 1 byte in that virtual per 1 word stored in output, and "end virtual" should close only nested virtual blocks not global one
2) override symbols org, virtual, $, $$ - no idea how.

_________________
I don`t like to refer by "you" to one person.
My soul requires acronim "thou" instead.
Post 02 Jun 2022, 08:12
View user's profile Send private message Send e-mail Reply with quote
bitRAKE



Joined: 21 Jul 2003
Posts: 3482
Location: vpcmipstrm
bitRAKE
I'm still thinking about the overall problem, but #2 can be realized in fasmg with the namespace separation mechanism. Here is another example, and this one.

_________________
¯\(°_o)/¯ unlicense.org
Post 02 Jun 2022, 09:20
View user's profile Send private message Visit poster's website Reply with quote
bitRAKE



Joined: 21 Jul 2003
Posts: 3482
Location: vpcmipstrm
bitRAKE
Maybe preventing any odd byte output is another solution? In fasmg there are a limited number of data directives at the bottom of the hierarchy - they could be overloaded with a calminstruction which limits output. Similar to how relocations are accumulated and alignments are verified.

_________________
¯\(°_o)/¯ unlicense.org
Post 02 Jun 2022, 09:31
View user's profile Send private message Visit poster's website Reply with quote
Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 8026
Location: Kraków, Poland
Tomasz Grysztar
The AVR.INC in the classic examples for fasmg does this by overriding label definition with "(label) ?" macro definition:
Code:
calminstruction (label) ? definition&
        local command
        match : command?, definition
        jno other
        match :: command?, definition
        jyes other
        arrange definition, =LABEL label =AT =$ =shr 1
        assemble definition
        assemble command
        exit
    other:
        arrange definition, label definition
        assemble definition
end calminstruction    
See also the chapter called "How are the labels processed?" in fasmg.txt.

The AVR.INC also defines PC symbol to be equal to ($ shr 1), to be used in expressions where you need current address. In another of my early examples, one for DCPU-16 I override the $ symbol itself:
Code:
; The following statement defines case-sensitive "$", while the internal "$"
; is case-insensitive (like all built-in symbols). Because such name has only
; one case, this definition effectively replaces the internal symbol unless
; the "$?" construction is used to directly access the case-insensitive one.

$ equ ($? shr 1)    
The DCPU-16 example was a conversion of macros originally made for fasm 1, which became mostly irrelevant and is not distributed in fasmg packages. With fasm 1 it is not possible to override standard label syntax and LABEL macro had to be used instead.
Post 02 Jun 2022, 10:22
View user's profile Send private message Visit poster's website Reply with quote
Display posts from previous:
Post new topic Reply to topic

Jump to:  


< Last Thread | Next Thread >
Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Copyright © 1999-2020, Tomasz Grysztar. Also on GitHub, YouTube, Twitter.

Website powered by rwasa.