[simh] RSTS processor identification

Johnny Billquist bqt at softjar.se
Sun Mar 7 17:42:33 CST 2021

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.
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 

Same with normal RSX, which is why you have to dedicate the whole 
controller to either DECnet or TT. You can't mix.

>> 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.

There was even a window system available, which sortof reminds of 
Windows before 3.1. Played a little with it. It works, but it's a bit 
limited. But from the pure graphics point of view, it's nice.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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