Safe to use $3FD - $4FF area when loading file

[RetroCoder]

I've got a decompressor routine that I use in my code and located it at $2000. Now I want to pack my xex file blocks and was wondering if I can move the decompressor to the tape buffer area @ $3FD - $4FF?  Is it safe for all DOS versions?

 

If not seen many programs use that space, so having a decompressor located there would be great. Extra benefit is that the code is exactly $103 bytes.  Maybe even a general packer could be written.

[kenjennings]

According to Mapping the Atari if you're not using the Cassette, FP package, or BASIC, looks like memory is free from $3FD through $6FF.

 

 

[baktra]

The cassette buffer will not be used by normal Atari DOSes  (DOS 2 family), as they do not want to interfere with the "C:" device.
I wouldn't be so sure for SpartaDOS like systems and also for those tiny "DOSes" that do not do anything else than load one binary file (MicroDOS, PicoDOS, PicoBoot).

There is never a guarantee. You would need to consult docs of the respective DOSes.

 

I believe a better option would be to decide with what DOSes you want your program to work with. And then choose the location for the depacker accordingly.

It is no shame to support only subset of DOSes on this platform.

 

 

 

 

[thorfdbg]

If this area is used only as temporary, then likely ok, though there is of course a hand full of software whose authors had the same idea. (-: For example, DDT (the Mac/65 debugger) uses this area for its temporaries. The most reliable and portable way would be to allocate space directly above MEMLO and relocate your code into this area. That's the "official" way.

 

[kenames99]

spartados 3.2d and 3.2c do not use that area. 3.2p, al 3.3 versions, and all current realdos versions do use that area. 

 

Ken

 

[RetroCoder]

Currently my packer asks for a location of a safe space and then locates the de-packer and the compressed data there. Once a piece is compressed into the right location the next file block is loaded into the safe space etc.  Works quite well if you know your program does not use a specific memory area.

 

Not writing a general purpose packer, but hoping to have one flexible enough for various programs.

 

The other advantage I have is that my level data is compressed and the same de-packer is already used in the game, so loading it at its final location as the first block in a file and then using it to unpack the rest of the program is a bonus

[phaeron]

The cassette buffer only extends to $047F. $0480-$06FF is considered user program memory (Atari OS Manual, section 4), with the caveat that the floating-point package can use part of it if used by the program. Thus, if you're concerned about conflicts with C:, only half of this memory is affected.

 

 

[Rybags]

$580-$5FF is generally used as the input buffer for Basic (usually E: input) and can actually overflow into page 6.  But the usage is temporary and you'd generally not have E: input going on during a load/compress operation.

[+CharlieChaplin]

Think if you are packing a ML program and it does not use/require Basic, then you can use pages 4, 5 and 6 safely. I am using pages 4 and 5 for Superpacker/Exomizer buffer and depacker since several years now without any problems. The only time when I cannot use that area is when the (unpacked) ML program itself makes use of these memory pages.

 

[Harry Potter]

Is it safe to use these areas with my cc65 programs?  I've been wanting to use some Low Memory areas with my cc65/Atari 8 programs. 

[thorfdbg]

Oh no, not again. Look, have you now understood how a binary load file works? This area is likely too small for compiled programs, and it is not generally safe to use, in particular to programs that using parts of the Os services. These are tape and printer buffers, and conversion buffers for the math pack functions.

 

In general, 0x1f00 and up is a good place for user programs, and not this area.

 

[sanny]

As I said before, the simplest way to use this memory area in cc65 is by calling _heapadd() [https://cc65.github.io/doc/funcref.html#ss3.5] so it becomes malloc()-able. To automatically load something there from the EXE file you need to add a load chunk.

[Harry Potter]

Can I load data into these areas from the main program?  That's what I'm doing on the CBM versions of my memory enhancements.

[Wrathchild]

Please take this back to your other thread... of course you can, as you have been told multiple times

[sanny]

1 hour ago, Harry Potter said:

That's what I'm doing on the CBM versions of my memory enhancements.

I'm wondering how you do that. Can you explain?

[Harry Potter]

I simply write the files in the config files with the starting address then use cbm_load() to load them into memory at the beginning of the main() function.

[sanny]

Hmm.  So you have code to explicitly load these areas.

 

You can do the same on Atari, where is the problem?

 

(Atari could do better by loading it automatically from DOS, but you seem to have problems implementing that...)

[+Stephen]

Relax and put away your tin-foil hat.  Commodore didn't destroy the free world.  This 7-year old playground mentality shit needs to stop.

[miker]

@Harry Potter

 

https://atariage.com/forums/forum/172-commodore-8-bit-computers/ - Commodore subforum

 

I don't believe Dumbledore hasn't told you...

[Irgendwer]

12 hours ago, Kyle22 said:

Harry, why do you talk about Commie shit here?

Because he was requested to do so.

Only dull people won't share and learn from principles applied in a similar field elsewhere...