Using the highest memory address

By Bit Addict

Resident (34)

22-05-2016, 10:01

What is the highest memory address an assembly program can safely use?

At address F197 the DPB (Drive Parameter Block) starts. Is it safe to use memory below F197?

By DarkSchneider

Paragon (1030)

22-05-2016, 10:36

I think is defined by SP.

By gdx

Enlighted (6431)

22-05-2016, 11:20

System variable "MEMSIZ" (at 0F672h).
The Drive Parameter Blocks are not in a fixed area. To know the DPB of each drive see the "DPBLIST" (at 0F353h ~ 0F363h).

By hit9918

Prophet (2932)

22-05-2016, 19:27

yes it is not ld hl,address but ld hl,(variable).
it is variable dependant on disk drives.
the highest one is HIMEM.
ld hl,(0xfc4a)
dec hl
thats the top byte you can use.
and the stackpointer goes somewhere below, need to reload it to be sure.

By gdx

Enlighted (6431)

23-05-2016, 10:08

By Metalion

Paragon (1628)

23-05-2016, 10:33

Nice, gdx.
Marked for future reference.

By santiontanon

Paragon (1831)

23-05-2016, 20:26

Nice figure! How come "BOTTOM" has a higher value than "MEMSIZ" given it's above?

By Metalion

Paragon (1628)

23-05-2016, 21:29

santiontanon wrote:

Nice figure! How come "BOTTOM" has a higher value than "MEMSIZ" given it's above?

"(address)" means the value stored at that address.
So "BOTTOM (0FCh48h)" means that the BOTTOM address is stored at 0FC48h.

By santiontanon

Paragon (1831)

24-05-2016, 02:52

Oh! I see! makes sense

By Daemos

Prophet (2169)

24-05-2016, 10:42

@Gdx. That image is so nice that it should be added to the WIKI.

By DarkSchneider

Paragon (1030)

24-05-2016, 11:04

Hi, according to the MSX technical handbook, MEMSIZ is:

Quote:

MEMSIZ (F672H, 2)
contents: highest address of memory used by BASIC

So maybe is not what you want if your environment is not BASIC. The map can vary if you use binary (ASM) program, with 4000-7fffh available (in that picture is shown as used by BASIC interpreter), or DOS, with also 100-3fffh available.

But, concerning the question, MEMSIZ could not have the highest one to use if not using BASIC. It would be good if someone knows about this.