On Sat, Jul 08, 2023 at 09:27:44PM -0400, Bill Degnan via vcf-midatlantic wrote:
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've used print and echo TTY tests on straight 8. BSW is not valid for straight 8 so tests will give different results after BSW. IAC with rotate are also invalid but didn't see any in quick look. Don't remember seeing straight-8 specific toggle in tests. http://www.pdp8online.com/pdp8cgi/query_docs/tifftopdf.pl/pdp8docs/toggle_in...
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@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@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.