digger wrote on 2025-03-03, 13:30:

Jo22 wrote on 2025-03-03, 13:04:

^DOS=HIGH does have an effect on an PC/XT in MS-DOS 6.22, if USE!UMB.SYS was being loaded. I tried myself, with a non-intelligen […]
Show full quote

^DOS=HIGH does have an effect on an PC/XT in MS-DOS 6.22, if USE!UMB.SYS was being loaded. I tried myself, with a non-intelligent UMB card.
I tried it together with UMB setting: DOS=HIGH, UMB

Of course, there's no HMA in XTs, but MS-DOS 6.22 does upload more DOS data into UMB if the HIGH setting is set additionally.
It will also complain with a message similar to "HMA not available, use lower memory", which can be ignored.

Cool! I didn't know that. Thanks for sharing that tip!

Hi again, I did forget something! I had to load STOPMAX.SYS on top of config.sys as a device driver, which supressed DOS to auto-load into non-existant HMA (on an PC/XT).
Otherwise, without the driver, the MEM command would be confused and DOS would end up at the bottom of conventional memory.
I checked that with CheckIt! v3. With the STOPMAX/DOSMAX, most of DOS kernal moved correctly into UMBs, leaving merely 9KB in conventional memory.

Hi,

do i need to solder a PSRAM to teensy or does it work without one too?

Thanks

matze79 wrote on 2025-06-07, 12:25:

Hi,

do i need to solder a PSRAM to teensy or does it work without one too?

Thanks

It will work without it - just won't have any Expanded RAM.

On my IBM 5160 XT Mainboard it doesnt add any memory, it just hangs on 64Kb.
Without XTMax it workes fine, also Picomem has no problems.

On Schneider Euro PC 1 it backfills memory from 512Kb to 640Kb, but the BIOS never comes up.
SDCard works with Driver.

I developed the XTMax on an IBM 5160 so it should work in your machine. In the Arduino IDE did you try setting the Teensy's CPU speed to 800 or more MHz and the compilation optimization to Fastest?

I'm glad to hear the XTMax mostly works on your Schneider Euro PC except for the MicroSD BootROM BIOS. @mbucchia may have some ideas, but maybe you can first try relocating the BootROM's base to a different address such as 0xC8000 I case there is a conflict with some other expansion ROM you have in this machine.

This is a very neat project, but its combination of features means it could do much more with a crabby 5150 if you thought outside the box:

Since this thing can 'just provide' bootsector code, and can supply RAM in the >640k area (has to, to simulate lotech ems), then this comes to mind:

Small boot sector program, in a tiny nondos partition marked 'active', is executed which:

1) Copies option roms into ram > 640k that is owned by this card, then sets them read only

2)allocates a small chunk of >640k ram as scratch

3) initiates a scan of adapter rom region, and enumerates entrypoints for execution, and stores the list in that spot.

4) sets a stack for return for opt roms that dont change boot sequence (vga bios, et al) to return to in that small region

5) execute option roms

6) if no boot altering optrom found, (and we end on return to the landing pad), boot specified partition regardless of boot flag.

On a 5150, this would let optionroms get run, and the vector table properly set up, before DOS gets run.

If no xtide or scsi card is found to take over boot sequence, it boots the first primary dos partition, which contains DOS.

MicroCoreLabs wrote on 2025-08-09, 21:03:

I developed the XTMax on an IBM 5160 so it should work in your machine. In the Arduino IDE did you try setting the Teensy's CPU speed to 800 or more MHz and the compilation optimization to Fastest?

With overclocking it, teensy works on 5160. Counts to 640Kb and also executes SDCard BIOS.
Did not retry the Euro PC yet, it has no other Option ROM installed.
But now also the BIOS shows up on the IBM 5160.

Is it possible to create SDCard from Windows / Linux ?

Hi,

is it hardcoded to 8Gb SDCard ?

i tried several SDCards from 64Mb to 2Gb Size, only my 128Gb and 32Gb Card works.
The smaller ones can't be partitioned, it always gives error during fdisk or not detect it at all.
Strange is it shows every Card up as 8Gb HDD.

On my 128 GbSDCard i created a 8024Mb Partition with FAT32, but i can only format the partition with 2048Mbyte (Fdisk shows 8Gb Size).

matze79 wrote on 2025-08-18, 17:08:

Hi, […]
Show full quote

Hi,

is it hardcoded to 8Gb SDCard ?

i tried several SDCards from 64Mb to 2Gb Size, only my 128Gb and 32Gb Card works.
The smaller ones can't be partitioned, it always gives error during fdisk or not detect it at all.
Strange is it shows every Card up as 8Gb HDD.

On my 128 GbSDCard i created a 8024Mb Partition with FAT32, but i can only format the partition with 2048Mbyte (Fdisk shows 8Gb Size).

Not hard coded as far as i know. Maybe try DOS 6.22 tools or FAT16.