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Model 4 boots from FreHD !

V

veco

Experienced Member
Joined
May 12, 2013
Messages
95
Hi.

I had some spare time (thanks to vacation days!) and I added the capability to boot from FreHD on my model 4.
So far, I am able to boot
- LSDOS 6.3.1
- CPM 2.2
- LDOS 5.3.1

The code is not 100% polished yet, but it works nicely. You don't have to patch the OS (unlike the 4P), it's all done during runtime. You need a patched ROM C, which detects if FreHD is present. If not, the usual boot flow is followed. If FreHD is present, the code attempts to download more boot code from the FreHD's eeprom. If that fails (FreHD not ready or firmware too old), back to the old boot flow. The new boot code now tries to download the final boot code from a file located on the SD card. Again, if the file is missing (or if <space> is pressed) old boot code. Next, the code checks some flag in the hard drive image header. If auto-boot is set and if the OS is recognized, the boot sector is read and patched, and the OS boots from HD.

I plan to create a utility to modify the hard drive image file header automatically, so that the parameters required for the patch (LSDOS) are stored automatically. Something like "vhdutl (autoboot=yes|no)"...

Will now try on my model 3 to autoboot LDOS 5.3.1, then will attack newdos... too bad I don't have a model I, but the same principles will apply.

-Fred
 
So where does one obtain a patched "C" ROM? unless we can come up with a EEprom or Eprom that is pin caompatible with the Motorola ROMS.
 
Chromedome45 said:
So where does one obtain a patched "C" ROM? unless we can come up with a EEprom or Eprom that is pin caompatible with the Motorola ROMS.
Click to expand...

The motoroal eproms are pin-compatible with the usual 27xx. I didn't have a 2716 available, but many 2732, so I burnt my patched code twice (actually, only the upper high matters, since the highest address bit is tied to +5V on the motherboard (if you use a 2732, of course)).

I am happy to give my patched code to anyone who wants to beta-test this. You will need :
- a 2716 or 2732 eprom, and a way to program it
- a FreHD with firmware 2.11
- a model 4

I will be testing on my model 3 soon, probably today.

-Fred
 
Well Veco you know me Mr. experimentor. Send me the files. You have my e-mail. I have a burner and an eraser. And a few 2716'a
Oh and I do beleive the Model III uses the same "C" ROM as the 4. When I was trouble shhoting my one model 4 board I swapped the
Model 4 ROM's into the Model III and it booted up normally. Which actually suprised me but looking closer they had the same part numbers!
 
veco said:
Hi.

I had some spare time (thanks to vacation days!) and I added the capability to boot from FreHD on my model 4.
So far, I am able to boot
- LSDOS 6.3.1
- CPM 2.2
- LDOS 5.3.1
Click to expand...

That's great news! I'm looking forward to using that once the dust has settled. (Hopefully Ian will be able to supply a drop-in EPROM along with the new FreHD firmware :D). I guess that being able to boot into CP/M 3 should also be possible, I'm mainly using CP/M 3 on my FreHD but of course am still booting from a floppy.
 
I'm happy to sell a Rom C upgrade product for Model III/4 when all the testing is completed.

Here's a question for everyone. Currently the space needed in Rom C is liberated by taking away the 500 baud tape load routine. Essentially this means you lose the ability to load model 1 500 baud tapes into the computer. This may present a problem for people who like to collect old TRS-80 tapes on eBay and then load them into their systems.

Just be aware of this limitation.

Ian.
 
TRS-Ian said:
I'm happy to sell a Rom C upgrade product for Model III/4 when all the testing is completed.
Click to expand...

Cool, I'm looking forward to that.

This may present a problem for people who like to collect old TRS-80 tapes on eBay and then load them into their systems.
Click to expand...

I'd imagine that it is definitely a consideration for Model III users, but less so for Model 4 users. Anyway, I assume that the ROM change is easy to temporarily reverse if necessary.
 
2732 with the standard rom in one half, Veco's rom in the other and connect the high address line to a switch - best of both worlds;-)
 
cluttered said:
Cool, I'm looking forward to that.



I'd imagine that it is definitely a consideration for Model III users, but less so for Model 4 users. Anyway, I assume that the ROM change is easy to temporarily reverse if necessary.
Click to expand...

Actually, there is no such limitation on a model III. I started with this rom, and I found enough space to fit the hack. (I can provide details, but basically, the C rom does a "check computer version" by reading a byte in rom A or B. Since this byte is always fixed (01h in my rom), I removed some of the code which handles the case where the byte is not 01h. I wonder if any such rom exists...

For model 4, I started hacking the rom directly, and didn't spend enough time on it to reclaim some space, but I am convinced that it is doable.

Finally, you lose the ability to WRITE at 500 bauds. You can still read/write at 1500 bauds, and read at 500. So I believe the limitation is really small. Who is still writing tapes at 500 bauds these days ? [just curious]

And I can confirm that my model III boots LDOS 5.3.1 from FreHD. I took a video, will try to post it on youtube.

-Fred
 
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