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

[David Gesswein]

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.