Far memory support for MSX about z88dk HOT 11 CLOSED

I've not had any thoughts about adding far support to any other machines - it was needed on the z88 because the OS was built around 3 byte pointers and provided allocation features (albeit only up to ~250 bytes).

For machines without such restrictions, and access to banks of contiguous memory, I think it's easier to just use Named address space

from z88dk.

Thank you for your answer. I've read your link. I'm developing for MSXDOS2, so I know how to manage the memory mapper by calling EXTBIO. But it's not clear to me the meaning of:

void setb0(void);            // The function that sets the currently active memory bank to b0
void setb1(void);            // The function that sets the currently active memory bank to b1

Moreover, I tried the linked example, but it seems that both files (bank1 and bank4) end on the same bank:

The first line ("Value in address space 1 is..") should be 89.
Thanks

from z88dk.

... my fault, I was using the emulator in 48k mode. With 128k it works!
Anyway, can you explain what does "sets the currently active memory bank to b0" mean for MSXDOS2? Thanks

from z88dk.

It means that we simply page in that bank into the memory space. In that example, I named the address spaces after the bank indices because I thought it was simpler and tied in with the general way banking is done within z88dk

For the MSX2, you'll need to maintain a map of physical to logical banks. So for allocation you've probably got code like this:

    ld      b,0             ;Primary mapper
    ld      a,0             ;Allocate user segment
    call    ALL_SEG
    jp      c,print_message_pop
    ; a = allocated segment

And then you'll need to keep track of logical to physical map:

    ; e = logical bank
    ; c = physical bank
    ld      hl,bank_mappings
    ld      d,0
    add     hl,de
    ld      (hl),c         ;Save mapping

bank_mappings: defs 256

So to switch to implement setb0 and setb1 the code would look like this:

_setb0:
    ld    a,(bank_mappings)
    call    PUT_P2  ;page the bank into segment2
    ret

_setb1:
    ld    a,(bank_mappings+1)
    call    PUT_P2  ;page the bank into segment2
    ret

ALL_SEG and PUT_P2 are obtained from EXTBIO:

    xor     a
    ld      de,$0401
    call    $FFCA   ;EXTBIO
    xor     a
    ld      de,$0402
    call    $FFCA   ;EXTBIO
    and     a
    ld      de,msg_nomapper
    jp      z,print_message
    ld      de,dos2_jump
    ld      bc,dos2_end - dos2_jump
    ldir

The code snippets have been pulled out from lib/target/msx/classic/msxdos.asm - if you use the pre-existing banking support it will load code/data into the appropriate banks and maintain the logical-physical mapping for you. So all you'll need to do is to provide setb0, setb1 and add a cheeky PUBLIC bank_mappings to msxdos.asm (I'll export an identifier by default so you won't need to do that forever)

from z88dk.

Thanks a lot!

from z88dk.

Hi @suborb ,
do you have any plan for the "I'll export an identifier by default" part? :-)
Thanks!

from z88dk.

To be honest, as you can probably guess I completely forgot!

from z88dk.

No problem! I hope you'll add it, when you'll have the time! :-D

from z88dk.

Just reopening so I don't forget again!

from z88dk.

Sorted - I've updated the example so that it works on msxdos as well. Hopefully your version looks at least somewhat similar!

from z88dk.

That's great! Thanks a lot!

from z88dk.