Altirra and D8:

[reifsnyderb]

Hello,

 

I am running Altirra 4.10 and have a question about drive 8. 

 

Drive 8 emulation is turned off under File/Disk Drives.

 

Originally, I had the emulated system setup for the following:

Atari 600XL/800XL

OS v 2

RAMBO -- 320k

 

When I booted with a DOS 2.5 boot disk ATR, I got the expected 128k RAM Disk on D8:

 

So, to eliminate D8, I first removed all files but DOS.SYS and DUP.SYS on the ATR.  Going into the DOS menu, I still found I had a D8 with 999+ free sectors.  (The number of sectors changed.)

So, I dropped the memory down to 16k without any extended memory.  I still have a D8 with 999+ free sectors.

 

When I compared this with real hardware on a 600XL w/320k of RAM, I don't have a D8:  This tells me that the issue is some setting in Altirra.

 

How do I turn that off?

 

Thanks!

 

 

 

 

Edited August 31, 2023 by reifsnyderb

[flashjazzcat]

Change the contents of location 5439 ($153F) to ATASCII "1" and write DOS to disk to permanently remove the RAMDisk.

[reifsnyderb]

44 minutes ago, flashjazzcat said:

Change the contents of location 5439 ($153F) to ATASCII "1" and write DOS to disk to permanently remove the RAMDisk.

I just checked and $153F already is $31 (or ATASCII "1")

[Kylev]

reifsnyderb,

Can we assume that you rebooted the Atari after you made the changes to the ATR?

Also, did you write DOS back to the ATR after you removed all files except DOS and DUP?

[reifsnyderb]

35 minutes ago, Kylev said:

reifsnyderb,

Can we assume that you rebooted the Atari after you made the changes to the ATR?

Also, did you write DOS back to the ATR after you removed all files except DOS and DUP?

I didn't change a thing.  It already had $31 at $153F.

[phaeron]

The $153F POKE from the DOS 2.5 manual is for where MEM.SAV and DUP.SYS get loaded from; I don't think it controls the presence of the RAM disk.

 

I deleted RAMDISK.COM off a copy of DOS 2.5 and wrote it out to a physical disk to boot on my 64K 800XL. It produces the same behavior as in Altirra in allowing access to D8: but showing 0 sectors free, so I'm not sure what determines whether D8: is accessible, if it is even conditionally visible. I haven't been able to set up a situation where it isn't.

 

The 16K case is more interesting. I can reproduce the 999+ sectors free, and from the execution history it looks like DOS 2.5 is reading nonexistent memory:

 

          40300:240: 83 | A=14 X=FF Y=01 S=EE P=74 ( V I  ) |     14AF: A0 7F             LDY #$7F
          40300:240: 85 | A=14 X=FF Y=7F S=EE P=74 ( V I  ) |     14B1: 28                PLP
          40300:240: 89 | A=14 X=FF Y=7F S=EF P=70 ( V    ) |     14B2: 90 09             BCC $14BD
          40300:240: 92 | A=14 X=FF Y=7F S=EF P=70 ( V    ) |     14BD: B1 32             LDA (BUFRLO),Y ;$74FF
          40300:240: 97 | A=FF X=FF Y=7F S=EF P=F0 (NV    ) |     14BF: 91 43             STA ($43),Y  ;$1480
          40300:240:103 | A=FF X=FF Y=7F S=EF P=F0 (NV    ) |     14C1: 88                DEY
          40300:240:105 | A=FF X=FF Y=7E S=EF P=70 ( V    ) |     14C2: 10 F9             BPL $14BD
        + Last 4 insns repeated 127 times

 

If a 16K configuration is used in Altirra with the 65XE/130XE base system, the DOS listing produces garbage because it is pulling open bus data instead of $FF. Either this is a straight bug in DOS 2.5 or there is some step necessary other than deleting RAMDISK.COM to disable the RAM disk access.

 

If anyone has a 16K system, I would be interested in whether it is open bus or not in unmapped areas (e.g. PEEK(32768)).

 

[reifsnyderb]

1 hour ago, phaeron said:

If anyone has a 16K system, I would be interested in whether it is open bus or not in unmapped areas (e.g. PEEK(32768)).

I pulled the 320k 1090 card and checked.  With a PEEK(32768), I get 255.  This would be right as the 600XL schematic shows the data bus is held high via 8 10k ohm resistors.

 

It sounds like this problem I found is some sort of DOS bug.  I've never checked for D8, without a RAM Disk, until now and was surprised to see DOS is reporting something there.