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Re: Siemens PC-D [Re: anyfoo] #117500 07/06/20 01:35 AM
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Separate post, because I don't expect many people reading that wall of text that is my previous post about MMU details:

If anyone has an actual PC-X, it would be amazing if you could upload some detailed pictures of the MMU, and maybe even dump the (presumed) ROM.

If the MMU indeed contains an 8086 and a ROM for some reason, the program in there could go a long way in understanding those missing details. But even just pictures would help, in case you don't feel like taking your PC-X apart too much.

Last edited by anyfoo; 07/06/20 06:51 AM.
Re: Siemens PC-D [Re: rfka01] #117501 07/06/20 02:57 AM
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There's a PC-X at http://www.geekdot.com/siemens-pc-x/. I don't know what the MMU would be there though as the board looks exactly like the PC-D.

Re: Siemens PC-D [Re: rfka01] #117502 07/06/20 06:23 AM
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Yes, I suspect the MMU is not actually shown there. Though I'm also not quite sure where it would plug in on that board. It's also unfortunate that that 20 year old slashdot comment is very light on details.

Re: Siemens PC-D [Re: rfka01] #117503 07/06/20 07:02 AM
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@crazyc, did you see the picture of the PC-D I linked in my post, with the bare "MMU" chip? Is there any chance that this is, after all, more than just a memory controller?

Re: Siemens PC-D [Re: rfka01] #117505 07/06/20 10:34 AM
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Oh weird. Did SINIX 1.2 work before? I just found out that it writes some page table entries with port 86xx instead of 84xx. The installation disks don't do that, but the fully installed system on hd does.

Last edited by anyfoo; 07/06/20 10:34 AM.
Re: Siemens PC-D [Re: rfka01] #117509 07/06/20 02:48 PM
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If the MMU indeed contains an 8086 and a ROM for some reason

I very much doubt this, performance would be terrible if a '70s-'80s era cpu had to look up an address translation for every memory access. It's very likely to be fast discrete logic and pals or an asic.

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@crazyc, did you see the picture of the PC-D I linked in my post, with the bare "MMU" chip? Is there any chance that this is, after all, more than just a memory controller?

You're right, that's just a simple dram controller. The 8207 does connect to the cpu io/mem status lines so it possibly could be replaced with a chip that does dram control and mmu functions with the same pinout (this does seem unlikely but the mmu has to sit between the cpu and the ram and the dram controller does too).

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Oh weird. Did SINIX 1.2 work before? I just found out that it writes some page table entries with port 86xx instead of 84xx. The installation disks don't do that, but the fully installed system on hd does.

I never fully installed it but rfka01 couldn't get it to work either https://forums.bannister.org/ubbthreads.php?ubb=showflat&Number=107533#Post107533. If you can figure it out it would be helpful.

Re: Siemens PC-D [Re: crazyc] #117510 07/06/20 06:52 PM
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Originally Posted by crazyc

I very much doubt this, performance would be terrible if a '70s-'80s era cpu had to look up an address translation for every memory access. It's very likely to be fast discrete logic and pals or an asic.


Oh absolutely. No way a slower CPU sits on the bus as an arbiter for memory accesses. The only reason I can imagine an 8086 there is if that thing is more complex than thought, but I'm not sure what the 8086 would do. Effecting configurations changes? But that's a bit much for what we know the MMU to do so far, then.

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You're right, that's just a simple dram controller. The 8207 does connect to the cpu io/mem status lines so it possibly could be replaced with a chip that does dram control and mmu functions with the same pinout (this does seem unlikely but the mmu has to sit between the cpu and the ram and the dram controller does too).


Yeah, although it seems unusual (the chip would essentially have to be a 8207 with an additional MMU, which seems weird), that is a possibility. I've asked the owner of the PC-X to look around for a daughterboard, which they agreed to do. If there is none, maybe they are okay to take the chip out and take a picture of it. At least that should tell us whether it's still an 8207.

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I never fully installed it but rfka01 couldn't get it to work either https://forums.bannister.org/ubbthreads.php?ubb=showflat&Number=107533#Post107533. If you can figure it out it would be helpful.


Yeah, just treating any access to 86xx as if it was 84xx is enough to make SINIX 1.2 boot and login (together with the other changes mentioned before, but I don't think they matter much for well-behaved programs). I haven't looked yet into what the difference between using 86xx vs 84xx could be.

Re: Siemens PC-D [Re: rfka01] #117511 07/06/20 08:44 PM
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Hmm, seems like SINIX 1.2 added support for an "Excelan EXOS 206 intelligent Ethernet controller". That would be interesting, but it seems to have its own CPU (hence the "intelligent"), so without hardware access to dump its ROMs...

Re: Siemens PC-D [Re: anyfoo] #117513 07/07/20 01:42 AM
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Originally Posted by anyfoo
Hmm, seems like SINIX 1.2 added support for an "Excelan EXOS 206 intelligent Ethernet controller". That would be interesting, but it seems to have its own CPU (hence the "intelligent"), so without hardware access to dump its ROMs...

Not necessarily, a bunch of these intelligent network controllers don’t have firmware in ROM. They start with the CPU stopped and wait for the driver to upload the firmware blob to shared RAM.

Re: Siemens PC-D [Re: rfka01] #117514 07/07/20 02:52 AM
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Thanks, Vas. I will dig around for that, but I have a hunch that I might not find it. Generally the SINIX kernel is pretty lean, and almost all of the bigger high entropy regions from my memory dump I've seen so far contain 80186 instructions that seem to be part of SINIX. I did not look at all of it, though, and it's always possible that it was in a segment that gets dumped after initialization, which would make sense.

I also found the initialization code for a "SERAC board", which I guess stands for "serial access board", but that, too, seems to have at least some firmware (though I guess this one is at least more likely to contain it as part of the driver).

I did not see any other, simpler serial port interface that would allow a getty or UUCP so far, which is a bit of a bummer. The "reserve" USART does not seem to be addressed at all in the kernel... though maybe the one designated to the printer could work?

And in slightly unrelated news, I was slightly wrong about my NMI bit 2 explanation above: It's not fully ignored during initialization (which includes the just mentioned driver initializations), the kernel also sets a flag in memory. Driver initialization uses that to check whether an NMI occurred during the early stages of trying to talk to the device, and if so, the device is skipped, since a bus timeout indicates absence of the device. I think bit 2 is then simply the bus timeout bit.

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