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Bootstapping Cromemco 4FDC

So I've verified that cdos107_5.tbz is a SSSD 5.25" CDOS that boots. However...it isn't IMD format but a raw dump. So I'm going to look around to see if there's an IMD version of it somewhere.
 
Amardeep-AC9MF said:
Nice finds! I was going by Github and Dave's Old Computers archives. I didn't realize unix4fun had stuff beyond what was included with z80pack and I had recently browsed through DeRamp so should have realized that one at least. Well, that certainly solves the boot disk problem.
Click to expand...

Is it possible for you to figure out what disk format the IMD image files on the deramp.com web site are for? Hopefully those are the 5.25" SSSD disks we are looking for.
 
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I feel better now that I've seen the files again at DeRamp and they are just letter salad for the naming. I never would have guessed that was the contents of that file.
 
So Now I need some clarification. I am noticing that I don't even have single density disks! I have SS/DD and DS/DD. Am I going to need single sided single density floppies to do this? I was just about to try writing the CDOS 1.07 image to disk when I realized this.

The Tandon 100 drive is capable of DS/DD disks, but yet it will still work with a single density controller?
 
Endersending said:
So Now I need some clarification. I am noticing that I don't even have single density disks! I have SS/DD and DS/DD. Am I going to need single sided single density floppies to do this? I was just about to try writing the CDOS 1.07 image to disk when I realized this.

The Tandon 100 drive is capable of DS/DD disks, but yet it will still work with a single density controller?
Click to expand...
Double density disks can be used for both single and double density recording. You can use a double-sided disk for single-sided recording.
All drives in the TM100 series can read/write both SD and DD. The recording method is determined by the floppy drive controller it is connected to.
The TM100-1 is a single-sided drive, the TM100-2 is a double-sided drive.
The TM100-2 can record either single or double sided disks, and again the recording method is determined by the floppy drive controller it is connected to.
 
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To build a little further on that, all 5.25" non-high-capacity soft sector media* is essentially identical. Even single sided or single density disks can be formatted as double sided or double density. They are not technically different, just tested to different levels of rigor. So other than taking on a little bit of risk it's not really an issue. I've not seen an issue in over four decades of using floppy disks. Now, 8" disks are also interchangeable for density, but single vs double sided are physically different. The jacket has the index hole in a slightly different angular position on double sided disks so they are not interchangeable.

*One notable but rare exception. Very early 35-cylinder diskettes had a shorter head access window than all later diskettes that could support 40 cylinders.
 
As of right now it is not working. The drive light comes on and the motor spins but the head is not moving.
I know the floppy drive works. I have it jumpered to Drive select 0 attached on a cable before the twist. The condition of the card is unknown. It was missing a few ICs when I received it and with all of the capacitors and wires stuck on it I am not sure what to expect. I replaced the 7404 that was missing and the WD1771 from another card. Rdos works fine. I will try some RDOS commands and see if I can load something that way

I tried the other image and IMD got mad:
imd.jpg
I assume this is because my floppy controller does not support 128 byte sector size?
 
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Ok, so if you got no errors writing the 2.17 then it was probably double density. That would explain why it just sits on the boot track with no activity. The 1.07 is definitely single density given the photo above, but yeah it looks like your controller is choking on that sector size. So it might work after your Adaptec arrives.
 
Amardeep-AC9MF said:
Ok, so if you got no errors writing the 2.17 then it was probably double density. That would explain why it just sits on the boot track with no activity. The 1.07 is definitely single density given the photo above, but yeah it looks like your controller is choking on that sector size. So it might work after your Adaptec arrives.
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Alternatively, you can use the Gotek/Flashfloppy combination. The IMD image file will need to be converted to either an IMG or HFE format file for use on the Gotek, using the HxC floppy emulator software.
The HxC utility is a free download, and you can see the manual here:
 
I received the adaptec aha 1542B controller and it seems to create successful images. However the IMSAI machine is not booting. when I type ;b into RDOS I hear 3 moves of the floppy head. I think seek to track 0 and then 2 seeks after that and then it stops. I am going to try some different images and maybe this controller can image 8" floppies.
The image I have tried so far is 019C0107.IMD. I am not sure if there is anything other information that could be helpful. I will keep trying different images
I do have a question. I am attempting to convert cdos0020_5.dsk to an IMD but I am not sure the correct way to do this. The last IMD image I used had the first 2 sectors as 128 and the rest were 512. I see from the documentation of BIN2IMD that you can set the sector number map but How would I know what it needs to be?
Am I correct to use disk mode 1, 300KHz FM? 40 tracks, 9 sectors a track? single sided since the image would be single for a SS/SD?
 
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What is the memory configuration in that machine? CDOS on that disk might be configured for a 64KB system. Cromemco boards bank switched RDOS out from C000h and replaced it with RAM during the boot process.

EDIT: I scrolled up and saw you are using a 32KB static RAM board. That might be why it didn't complete booting. So you need to make a decision at this point depending on how you want to build up your system. Do you want a full Cromemco compatible platform? If so you're going to need a memory board that will work. If CP/M and CDOS are enough, most boards can work if you can stack up 64KB. The upper 32KB board does need to support the PHANTOM signal and you'll need to modify the 4FDC to generate that signal. Cromemco relied on bank switching so didn't drive PHANTOM, if I recall correctly.

Or you could acquire a 64KZ or 64kZ-II memory board. Don't buy the one that same vendor you got the 4FDC from is selling. It's missing an unobtanium part and it's unknown if anything else is broken on it.

If you're not specifically wanting a Cromemco system, you could consider getting a different FDC board that supports double density off the bat. But getting 64KB total will be needed for pretty much anything.
 
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With respect to the disk images, don't waste your time screwing around trying to convert formats. Going from a raw sector dump to a structured image like IMD is frought with details that you don't want injecting potential barriers when you're trying to do an initial bring-up. A known good IMD version of that should be available and I'll try to locate it. If anything has 512 byte sectors it indicates MFM so you won't be able to use it anyway.

Attached is the IMD of the CDOS 0020 5" disk.
 

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  • CDOS_0020_5_IMD.zip
    47.1 KB · Views: 2
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300kbps is only for writing MFM standard density on a high density drive. if you are using a high density drive on the Adaptec you are introducing yet another failure point which is the track width. Keep it simple and use a 360KB 40 cylinder drive to write the images.
 
I tried the image. The drive starts seeking and it seems to load into memory. From what I can tell, the first 8K get filled (80h I think would be the hex value).
I have 32K static ram. after 80h the memory looks more random as you step through it.
The machine acts funny after it does its loop and you stop the processor. The examine button act like examine next, like the machine doesn't completely reset or something is hung. I have to power cycle to get a good boot.
After that the machine seems to go into a loop. the drive keep seeking the same 3 or 4 clicks and the loop repeats.
I don't have a good way to take a video of the front panel and chop the file down so it will upload. Here are some snapshots of the front panel that will hopefully give a good picture to what the computer is doing.
IMG_20231209_193959707.jpgIMG_20231209_194001088.jpg
the WAIT light flashes steady and so does the MEMR and INP.
I am not experienced enough to be able to be able to step through the code and figure out where it messed up.
Maybe I can. Is there a way to look at the code of the 017C0020.IMD and figure out where stuff should be loaded?
Is there a chance there is bad logic on the 4FDC controller? Like a bad address bit and it's moving memory to somewhere it is not supposed to?
I have tried the 4FDC with switch 2(RDOS disable after boot) and 3(BOOT ENABLE) in different positions with no different effect.

I am writing the image with a Tandon TM-100 but I have a Fujitsu M2551A I am using on the IMSAI to boot. Should I be using the Tandon to boot?
I have found the power connectors very hard to pull off the Tandon drive so I am not switching it over to the other machine. I don't want to snap the power connector off the floppy drive.

A question about ImageDisk: I am using a double sided floppy drive and a DS/SD 360K disk. when I set up the ImageDisk settings for the floppy should I use 1 or 2 heads? the drive has 2 heads but the image only needs one. Either way seems to write fine. I wrote the image multiple times and same problems.

Thanks for all of the help. I wouldn't have been able to get this far with out it.
 
I haven't so far been able to find any documented information about whether CDOS is linked for a certain memory size or if it adapts dynamically at boot up. That could be crucial for this stage since you don't have the typical 64KB installed. I will keep looking, but in the meantime there are some mods that had to be done to the 4FDC to support CDOS. Check that your board has the fixes documented on page three of the attached bulletin.

Further, you might want to key in a memory test and run it to make sure the 32KB you do have is all working correctly.
 

Attachments

  • Cromemco Users Bulletin Issue 1.pdf
    533 KB · Views: 1
For the Image disk question, if you are writing a single sided image the contents of the second side don't really matter and Image disk would use the correct head of a double sided drive to write the image.

Since both your drives are 40 cylinder 48tpi they should be fine to have the Tandon on the PC and the Fujitsu on the 4FDC.
 
I've found in a later CDOS manual that it was in fact statically linked to a memory size. The 1.07 disk is set up for 64KB. I'm going to boot the 00.20 disk to see what that one is setup for.
 
Ok, confirmed the 00.20 is also set up for 64KB. So you'll need to get more RAM meeting the requirements outlined in my previous message (either Cromemco bank switch compatible or supporting PHANTOM with associated 4FDC mods).
 
I have a 64K board but it is dynamic so it doesn't play well with the front panel. I have 32K plus another 8K board of static. I would have to modify the ZPU board to refresh dynamic.
There are 4 options with keeping in mind that in the end I would like to be able to use my front panel to do the simple things an IMSAI is known to do.
1) Buy enough static ram to fill 64K.
2) Wire the ZPU to support refresh for the Measurement Systems and Control Inc. Model DMB 6400 and figure something later for the front panel later.
3) Setup bank selecting/phantom select stuff. (sounds complicated)
4) I bought a JAIR Single Board Computer that is not assembled but could be used as a last resort.

Thanks for the help
 
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