[vcf-midatlantic] Pdp-8 focal @ Kennett Classic

[Bill Degnan]

Do you have a source online for PDP-8 toggle in test programs, such as echo
characters to/from the TTY  and PDP-8?   THe PDP-8e versions are
different.  I can probably figure some of it out, like I did with the chase
the lights, but I am always up to make things easier.

I have loaded and run PDP 11 BASIC without a reader run relay.  The FOCAL
tape I have came from the former owner of the machine.

First though, I need to get the RAM to behave solidly, so I need to check
the diodes of the flip chips and measure what's happening to the best of my
ability. I can load simple programs like the chase the lights but I could
not load in the papertape loader successfully, ~20 instructions.

On Sat, Jul 8, 2023 at 8:35 PM David Gesswein via vcf-midatlantic <
vcf-midatlantic at lists.vcfed.org> wrote:

> On Sat, Jul 08, 2023 at 03:26:57PM -0400, Ethan Dicks via vcf-midatlantic
> wrote:
> > On Fri, Jul 7, 2023 at 10:39 AM Duane Craps via vcf-midatlantic
> > <vcf-midatlantic at lists.vcfed.org> wrote:
> >
> > But there's also pacing problems between chars.  The reason the DEC
> > LT33 adds the Reader Run Relay to the standard ASR33 is because if the
> > TTY is sending chars back to back but the PDP-8 is off processing
> > previous chars, it's going to fail to keep up and you'll lose chars.
> > It happens with the RIM and BIN loaders
> >
> I don't see how this can be an issue with standalone RIM and only an
> issue with BIN if you have two sections on the tape so 8 halts between.
> I've
> found the code path is short enough that any reasonable baud rate
> character
> time is longer than the time for 8 to be ready for next character. If your
> reading tapes under OS/8 or other OS then you do need reader run.
> For early 8's without buffered serial port reasonable is lower since you
> have less time till next character will corrupt current. I haven't done
> test/analysis to determine limit but think its worked for me at 9600
> without
> reader run. At 110 baud 1 bit time is 3000 3us instructions.
>
>
> > but it's especially pronounced
> > when reading programs into interpreted languages like FOCAL and BASIC.
> >
> The early FOCAL's I've been playing with use interrupts for the serial
> I/O reading into a buffer. The code isn't smart enough to turn off
> receiving
> to prevent overrun so the reader run doesn't help case I was discussing
> with
> the slight mismatch of baud rates. Code is hard to follow but their likely
> is an IOF in path of adding new lines so reader run probably helps their.
> Don't know if later FOCAL's improved this.
> For loading from PC I have a program that checks the echo back to prevent
> overrun at high baud rates.
>
> I haven't played enough with BASIC reading from console to comment.
>
>