I'm about to start porting a version of ANS Forth to the Sprinter, and I have a few questions ;-)

1. What memory segments are available for use by EXE programs? I see that normally DSS/BIOS is at $0000-$3fff, and the EXE loads at $8000. What is at $4000-$7fff?

2. Can the DSS/BIOS be paged out and replaced with RAM at $000-$3fff? Do interrupts need to be disabled if doing this?

3. Is it recommended to use the text I/O functions in DSS or the BIOS?

4. When exiting the EXE with BC=$0041/RST $18, does execution continue after the RST $18 (in other words, is it necessary to have the following RET?)

Thanks,

Garry


--
Garry Lancaster
http://www.z88forever.org.uk/zxplus3e/
http://www.z88forever.org.uk/

> 1. What memory segments are available for use by EXE programs? I see
that normally DSS/BIOS is at $0000-$3fff, and the EXE loads at $8000. What
is at $4000-$7fff?

Yes, the first segment ($0000-$3FFF) used for DSS or BIOS, when you call it
or interrupts coming.
The next segments ($4000-$7FFF, $8000-$BFFF, $C000-$FFFF) are available for
use EXE program.
But it has some features:
The system will build EXE prefix at the address (start address - $100).
Therefore you can't use the address of loading less than $4100.
The system will allocates and set memory only that need to load your
program. I.e. if a program loads to $4100 and it has length 10K, system
allocates one page (16K) and set it to $4000-$7FFF segment. In the next
segments will set page number $FF. If a program has length 20K, system
allocates two pages (32K) and set it to $4000-$7FFF $8000-$BFFF segments,
the last segment set to $FF.
About 'loads at $8000'. We recommended to use $8100 as start address for
the program and $BFFF as STACK address. If your programm are small than
$4000(16K). It will help to avoid mistakes in the first programm. But it's
not system requirement.

> 2. Can the DSS/BIOS be paged out and replaced with RAM at $0000-$3fff?
Do interrupts need to be disabled if doing this?

Yes, it can.

Replace

        DI             ; disable interrupts

        IN A,($82)     ; get page which set $0000-$3FFFF

        LD (DSSPAGE),A ; store dss page number

        LD A,your_page ;

        OUT ($82),A    ; replace it with your page.



Restore

        LD A,(DSSPAGE) ; restore dss page number

        OUT ($82),A    ; back dss page

        EI             ; enable interrupts

Thanks for your replies - very informative. I'm sure the memory allocation would have caught me out if you hadn't explained it!

Are there any issues with disabling interrupts for a long period of time (are they used to read the keyboard or something, for example)? I was considering paging out DSS/BIOS all the time (except when needing to call it) so I can use the whole 64K address space.

Thanks,

Garry



--
Garry Lancaster
http://www.z88forever.org.uk/zxplus3e/
http://www.z88forever.org.uk/

> Thanks for your replies - very informative. I'm sure the memory
allocation would have caught me out if you hadn't explained it!

Thank you for your question. It help us for more and best description of
Sprinter's features.

> Are there any issues with disabling interrupts for a long period of
time (are they used to read the keyboard or something, for example)? I was
considering paging out DSS/BIOS all the time (except when needing to call
it) so I can use the whole 64K address space.

If you don't want to lose data from keyboard or mouse, you have to write
interrupt handler at $0038 address.
Like this:

$0038

        CALL DSS_INT ;that placed at $4000 or more

        EI

        RETI

        ...

        ...

$4000

        ...

DSS_INT

        PUSH AF

        LD A, (DSS_PAGE)

        OUT ($82),A

        CALL $0038

        DI

        LD A,(YOUR_PAGE)

        OUT ($82),A

        POP AF

        RET