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a few DECmate II questions

I don't know OS/278 but it seems like RK50: and RX51: is how it refers the first and second floppy? That's what I am thinking anyway. Never used it.
 
The RX50 is an unusual drive.

Assuming RX50: is the top slot in the drive and RX51: is the bottom slot, I have to ask, Are you flipping the floppy upside down when you insert it into the bottom slot? On real DEC branded diskettes there is a mark that lines up with an indicator on the drive that you can see when the door is opened. On the top slot it is on the right and the bottom slot it is on the left. If the floppy is not flipped over when in the bottom slot the drive will not see the index pulse. And if the drive doesn't see the index pulse it probably doesn't think there is a floppy inserted.

I apologize if you already knew this but I have seen this cause confusion.
 
DougIngraham said:
The RX50 is an unusual drive.

Assuming RX50: is the top slot in the drive and RX51: is the bottom slot, I have to ask, Are you flipping the floppy upside down when you insert it into the bottom slot? On real DEC branded diskettes there is a mark that lines up with an indicator on the drive that you can see when the door is opened. On the top slot it is on the right and the bottom slot it is on the left. If the floppy is not flipped over when in the bottom slot the drive will not see the index pulse. And if the drive doesn't see the index pulse it probably doesn't think there is a floppy inserted.

I apologize if you already knew this but I have seen this cause confusion.
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Unless I misunderstand something @hush is using gotek floppy emulators, so there are no real floppy disks involved when he references "RX51:".
I am actually impressed that the gotek emulator worked as a RX50 using standard cabling. I was expecting some fancy cabling to make that work.
 
A quick look at the system device driver code seems to imply it implements SYS: in group RX50 as whatever device you've booted from. I didn't yet find any code for a non-system driver, which is weird.

Does the command "RES/E" say anything interesting?

I think there are some MAME folks working on an emulator. Maybe they've been down this road before?

Vince
 
Found it. It was hiding in "rx5a.pal". The device class is RX5A and the entry points are for RX50: and RX51:. The only difference between the entry points seems to be the unit bit is set in the parameter to the internal routine when RX51: is used.

Vince
 
I'm no expert on DECmate hardware, and certainly no expert on floppy disk issues, but I seem to recall that the RX50 drive has a single head positioning arm, so that seeks on the upper drive also seek on the lower, and vice-versa. This makes the pair behave as if the second was a sort of upside-down "head" of the first. I don't know if that's important, as the driver shouldn't be making assumptions about where the head was left during earlier calls. (Each call should seek, I think.)

But if it is important might be something that needs special attention to get right in the emulator.

Vince
 
slight misunderstanding on my part, you are correct, RX50/51 correspond to drive pair A and RX52/53 to drive pair B. did as recommended and set both up the same way but strangely enough, if i issue a DIR RX52: the only device that lights up is the first gotek, the one that i am booting from. the system also hangs without error after refreshing the screen. i think that has something to do with what i'm seeing, but the second gotek is physically connected to the second connector on the motherboard, i'm not using a ribbon cable to connect the two of them. in terms of cabling and jumper settings, the second gotek *should* be where i expect it, and it does not prevent the system from booting.

it seems like the first gotek is somehow "intercepting" the calls to the second, but with them both on separate ports i'm not sure why that would be. maybe it is something in firmware that isn't accounting for RX50 behavior?

edit: i've opened an issue with the flashfloppy developer just in case, seeing as i have tried multiple ribbon cable orientations and jumper settings for the second gotek and it still does not work i am truly at a loss. :)
 
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hush said:
it seems like the first gotek is somehow "intercepting" the calls to the second, but with them both on separate ports i'm not sure why that would be. maybe it is something in firmware that isn't accounting for RX50 behavior?
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The RX52: and RX53: devices, I believe should be part of the "RX5B" group, controlled by a different handler.

I'd expect "DIR RX52:" to hit the boot device briefly -- it will load DIRECT.SV from there and then branch to it. DIRECT should then load the RX5B driver (also from the boot device) and use that to access the other drive pair.

I'd expect that the emulator setups for the 50/51 pair and for the 52/53 pair could be identical and interchangeable, and the controller/cabling should differentiate them to the software.

If your system lacks the RX5B driver, I'd expect an RX52: access to give an error, not a hang.

Vince
 
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hush said:
i have the biggest smile on my face right now, that did it! i got a happy beep and a welcoming DECmate II screen this time, seems like she's good to go! .. :)
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This is impressive and very encouraging. Sounds like you have a DECmate II working with a non-DEC display (in place of a VR201)? If so, could you post a pic and/or a wiring diagram of what parts are needed and how they're connected? Which OSSC module/kit do we need? Do you have it working with a VGA or HDMI display? What resolution? Thanks for sharing your expertise.
 
i do have it working on a standard 16:9 HDMI display using an OSSC but if you are not interested in retrogaming or think the OSSC is a bit spendy, you could probably use any regular VGA to digital converter. the OSSC is an upscaler and the image seems quite clear on my display but i haven't tested a cheaper unit, so YMMV. you could probably also just hook it up directly to a VGA display. i documented the process with pinouts and parts here: https://wiki.syspro.gs/#DEC/PDP8/DECmate_II_VR201_cable_replacement.md

if you're going to buy an OSSC i recommend buying directly from VGperfection: https://videogameperfection.com/products/open-source-scan-converter/ it looks like they are out of stock for now though, unfortunately. like i said though, likely not necessary, just what i had lying around.

if anything is unclear just let me know!
 
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