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Bringing up hard disk with unknown parameters

NF6X

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I have a Tandy Fifteen Meg Disk System. The drive seems to be functional. I've dumped its contents with David Gesswein's MFM Emulator, and it seems to still be error-free after 30 years! Examining strings in the image suggests that it probably has LS-DOS 6.03 on it. I found these strings:

TRSDOS 06.02.00 - Copyright 1984 Logical Systems Inc.

and

LS-DOS 06.03.00 - Copyright 1986 Logical Systems Inc.

in the image.

Now I'm trying to access the drive with my Model 4P, and I'm not having luck yet. I'm a bit confused about how hard drives work in TRS-80 land. I gather that the RSHARD driver needs to be invoked with correct parameters to tell it the physical drive details and partitioning, but how do I figure that stuff out with a drive whose contents are unknown?

When I boot the 4P with the hard disk attached and nothing in the floppy drives, I get a blank screen. Inserting an LS-DOS floppy that I have gives me a "Disk Error" message. Resetting with PF2 pressed lets me boot that floppy normally. I use a FreHD on my Model 4, but with disk images that were created by knowledgable folks.

Can anybody help point me in the right direction?

The drive makes a lot of noise. Sounds like arthritic bearings, with occasional "sproing" sounds. I plan to leave it in place and functionally replace it with an MFM Emulator board tucked inside the box to save wear and tear on the real drive, but I'd like to try using the real drive a bit first for fun and edutainment. Here it is spinning up and down after I replaced the keyswitch (didn't have a key for the original) and the Rifa paper dielectric cap in the power supply (based on obvious cracking of its case, I'm sure it would have burst into flame under power):


I posted many pictures in my Twitter feed, and here are some highlights:

IMG_3468.jpg IMG_3464.jpg IMG_3466.jpg IMG_3471.jpg IMG_3474.jpg

Edited to add:
According the the MFM Emulator card, this drive appears to have 306 cylinders, 6 heads, and 32 sectors per track.
 
Last edited:

Stone

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Are you using the same HD controller? You're aware that a drive LLFed with one controller has little if any chance of running on another controller.
 

NF6X

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It should be the same controller unless something weird happened in its previous owner's hands. These Tandy external drives have the controller in the same box as the hard drive, and it connects to the processor bus on the computer with a 50 line ribbon cable. The drive itself appears to be just fine (though a bit noisy), based on reading it with the MFM Emulator card. This test doesn't touch the regular controller card, naturally. Assuming that the controller card still works, I should just need to figure out how to determine the driver parameters.

As I understand it, these systems were typically booted with a floppy disk that loads the hard disk driver with the necessary parameters for that particular hard drive. I think that the 4P's ROM supports booting from a hard disk without needing a floppy, but it was never officially supported by Tandy, and I think that it requires specific changes to the OS installed on the hard disk. Since this one didn't boot by itself, I presume that the installed OS hasn't been set up with the secret sauce for floppyless booting.

I may just need to figure out the driver parameters with educated guesses and trial+error, but I'm hoping that the TRS-80 hard drive experts might have some hints.
 
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NF6X

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Once I finish playing with it under LS-DOS, I think I'll probably try to use the box in my Model 6000 project, with the drive unplugged and replaced with the MFM Emulator card. Then maybe you can help me with the Xenix part!
 

NF6X

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This one is formatted with 32x 256-byte sectors, rather than 17x 512-byte sectors. The hard disk driver also needs to be told about partitioning, which isn't helpfully stored in a partition table on the drive as it would be on an MS-DOS system.
 

pski

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As you surmised, Mark, the partitioning configuration is stored on the boot floppy. AFAIK, there really is no way to figure out how it was partitioned without the floppy. However, you could try a hit and miss approach with RSHARD. I think it was fairly typical to partition in some equal fashion, like 6 partitions each with 1 head and 306 cylinders. Or 6 partitions each with 6 heads and 51 cylinders. 6 partitions is popular since most machines had 2 floppies which left 6 logical drives left. You can play around with rshard and you may get lucky.
 

NF6X

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I was just typing my new response as you posted that, Pete! By trial and error, I determined that there appear to be six partitions, one per head, spanning the full 306 cylinders. They are labeled "DONFTE01" through "DONFTE06". I didn't see anything exciting on then. Looks like LS-DOS is on partitions 2 and 3, and 1, 5, 6, 7 are empty (but formatted). Oddly, DIR lists each partition as having 153 cylinders. Is that some sort of weird logical-vs.-physical thing that LS-DOS does?

IMG_3477.jpg
 

NF6X

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So, I did a SYSGEN on my LS-DOS floppy, so now I can boot from that floppy and access the hard drive. I still need to boot with F2 pressed, though, or else I get a "Disk error". Maybe the 4P's auto-boot ROM is trying to boot from the empty first partition and throwing an error? I'll experiment some more.
 

pski

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I was just typing my new response as you posted that, Pete! By trial and error, I determined that there appear to be six partitions, one per head, spanning the full 306 cylinders.

Ha! What is that saying about minds that think a like?
 

NF6X

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I was hoping for a shortcut, but I just had to bang on the 4P's moderately dreadful keyboard until things worked. :)

I should try to see if I can bring up the drive image I made last night in an emulator. I can tell that the data came off, but I can't tell yet if the dumper utility stored it in a format that any of the TRS-80 emulators know how to use.
 

pski

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Tell us more about the MFM emulator your are considering. Is this a SS drop in for a MFM HD?
 

NF6X

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This one:

http://www.pdp8.net/mfm/mfm.shtml

I used mine last night to dump an image of the drive. It can either connect to a real MFM drive to read its contents, or emulate an MFM drive when connected to a vintage controller. I have only tried reading drives with it so far. Here's mine, plugged into the drive in this disk system in place of the original controller:

IMG_3474.jpg

The fuse is not original. The card includes a bank of super caps in series to hold up power to the BeagleBone Black (out of fight underneath the card) so it can shut down cleanly when power is turned off. One of the traces between them was accidentally made thinner than the others, and something odd and unexplained happened the first time I used the card that burned the trace open. I patched it with a fuse just in case the odd and unexpected event occurs again, using some 40-something year old pigtail adapters that I had lying around.

IMG_3458.jpg IMG_3459.jpg

I never figured out what happened to burn the trace, and the usual inrush surge when the caps first charge shouldn't be large enough to burn the trace. But maybe the trace was nicked or something, causing it to overheat when it got slammed with the 900mA or so inrush surge?

I'm thinking of ordering another card, so I can dedicate this one to living inside the disk system box and have another one sitting around for imaging old drives. The only other old MFM drive I have right now is one that came with an old CoCo (!) hard disk system, though, and it's not doing anything interesting until I fix the dead track zero sensor on its head stepper.
 

NF6X

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Oh, and I should have elaborated some more: The MFM emulator card has a BeagleBone Black hanging off the bottom to act as its brain. The BBB is a small, inexpensive embeddable computer board that can run Linux, among other things. It has an ethernet interface, and USB host and device interfaces. It's vastly smarter than whatever computer it's emulating an MFM drive for!
 

gslick

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I just sent David a payment for an assembled MFM emulator card today and should be receiving a BBB tomorrow so I'll be checking one of these out myself too. If they were less expensive I might have bought a couple of them to find interesting uses for them.
 

NF6X

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I'm excited to see that folks are finding out this cool emulator, and I'm looking forward to seeing more success stories involving it. I think that David did a fantastic job designing and building it!
 

NF6X

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Did you get an assembled one? I figured you as a build it yourself guy.

I am, but I got this one assembled with the BBB pre-installed. I already have enough projects, and I just wanted to use this as a tool rather than yet another project. I did already have a BBB, but I just wanted this to be close to turn-key.
 
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