[simh] RSTS processor identification

[Paul Koning]

> On Mar 7, 2021, at 6:42 PM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> 
> 
> On 2021-03-07 23:00, Paul Koning wrote:
>>> On Mar 5, 2021, at 9:02 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>> 
>>> On 2021-03-06 02:33, Paul Koning wrote:
>>>>> ...
>>> 
>>>> I would have liked better comms.  The USART has such a tiny FIFO that you can't run it at higher than 9600 bps even with the J-11 CPU.  At least not with RSTS; perhaps a lighter weight OS can do better.  The printer port is worse, that one can't run DDCMP reliably at more than 4800 bps.  I normally run DDCMP on the PC3XC, which is a 4-line serial card that uses two dual UART chips (2681?) with reasonable FIFO.
>>> 
>>> Hmm. I'm pretty sure I was running my -380 with the printer port for DDCMP on HECnet for a while, and at 9600 bps.
>> DDCMP runs fairly well on RSTS with the printer port at 9600, but I get some overruns.  My guess is that the terminal driver (which is front ending the DDCMP machinery) isn't as lightweight as the equivalent on RSX.  Or do you bypass the terminal driver and get a separate comms-specific driver for this case?
> 
> I realized I might have spoken too soon. There is also a comm port, and now I'm unsure if DECnet isn't running over that one actually.

That would make a difference.  The printer port is a 2661 on the Pro 350, or the gate array equivalent on the Pro 380.  Either way, it's a UART without a FIFO.  The comm port is an 8274, which has a 3 byte FIFO.  So does the 2681 dual UART, which is what the 4 port comm card uses.  In my tests, that FIFO makes the difference between running reliably at 9600 baud, and getting frequent overrun errors.

> Anyway, in RSX, when running DDCMP on the serial port, DECnet has its own device driver. So not talking through any terminal device driver, which have all kind of features and capabilities expected for a terminal line.
> 
> Same with normal RSX, which is why you have to dedicate the whole controller to either DECnet or TT. You can't mix.

That's probably more efficient.  In RSTS I added the DDCMP support as an "auxiliary" function attached to the terminal driver, so the regular terminal driver does the device control and then diverts the data stream to/from the DDCMP driver.  It's a bit like how Linux does these things, I forgot what term they use.  In fact, it would be possible to add DDCMP support to Linux in the same way if someone wants to try that... :-)

>>> But with P/OS, you are not using the console port as such. That's all on the graphics side.
>>> But unless I'm confused, that's the same port. The printer port just can also be the console port, if you short pins 8-9, right? Except it won't fully work the same as the DL11, since interrupts work differently. But polled I/O will work the same.
>>> But I would expect the speed characteristics to be the same for the console as for the printer port.
>> Correct, printer and console are actually the same thing.  If you use the console cable (pin 8 connected to 9) then that materializes a DL11-like CSR set at 177560.  Yes, with polled I/O such as the ODT microcode uses that works just like a real DL11, but for interrupts it's different.  In RSTS, either way that port becomes a terminal port.
>> RSTS does have support for the graphics module, in "glass TTY" mode within the initialization code and full VT220 emulation in RSTS proper.  Well, except for blink mode, and no bold in 132 column mode.
> 
> Well, in P/OS you do have the option of also play graphics, and do different resolutions. But the "terminal" handling for it have similar limitations. I think blink isn't working the same as in a VT100, nor is reverse (if I remember correctly). And of course, smooth scrolling do not work you you don't scroll the whole screen, since the hardware isn't capable, and doing it in software would be way too slow.

Right, I forgot about partial smooth scroll.  Blink could be done fairly easily with EBO through the color lookup table; I haven't bothered doing that.  Same for bold.  Reverse wasn't a problem in my experience.

	paul