Line input routine

[Mike Katz]

I'm rewriting a readable text paper tape punch program and I need PAL-8 routine that will input a line of text and return on carriage return.

The following features would be nice (for teletype, glass TTY or VT-100:

• Convert lower case to upper case
• Accept backspace and rubout
• Accept linefeed to display the line
• Accept control/X or ESC to delete the entry and start over again.
• Puts out a prompt
• Either null terminates the end of the string or stores the length of the string somewhere
• Maximum line length of 60 to 80 characters.
• Ring the bell when the buffer is full.

I could write this myself but I'm trying to save some time.

If you know of a package or routine like this, please let me know.

Thanks,

     Mike

[Steve Tockey]

Mike,

More questions need to be answered to see if anything is available or how easy it might be to write a new one:

1) Is this intended to be a completely stand-alone program (e.g., read in using BIN Loader)? Or, is it intended to be a program that runs in the OS/8 environment? The reason this is important in that some of the functionality you are looking for is already built into the OS/8 TTY: device handler but that can only be used if the program is running in the OS/8 environment.

2) If stand-alone, i.e., outside of the OS/8 environment, does it matter if it's running with interrupts on or not? I know for a fact that I have written this kind of code in the past but it was in an interrupts on-based application. OS/8 does not itself play well with interrupts on.

3) The string that gets returned should be unpacked? i.e., one 8-bit character per memory word in the buffer? In many PDP-8 applications, to save memory, characters get compressed to 6 bits then packed two in one 12-bit word. OS/8, by the way, packs three 8-bit characters into two 12-bit words.

4) Behavior on a Teletype could be very different than on a VT-100 regarding backspace and rubout. Whereas the VT-100 can erase the last character and move the cursor left, the "standard" PDP-8 behavior on a Teletype is to print a slash on the first rubout/delete followed by the character deleted for each rubout/delete press followed by another slash when the next character is no longer a rubout/delete. For example, if the user typed the sequence ABCEF<rubout><rubout>DEF it would get printed on the Teletype as:

ABCEF/FE/DEF

5) The "standard" in PDP-8 land is to use Control/U to erase everything, not Control/X

6) It is generally good practice to separate input from output in a situation like this (AKA high cohesion & loose coupling / Single Responsibility in the SOLID sense). I mean, printing a prompt should not be a responsibility of this function because it limits its applicability. You should have a separate output routine that prints stuff. Call the output routine that prints the prompt, then call this routine to get the input.

Finally, how soon is this needed?

Cheers,

-- steve

[ggrinton]

Although it is nearly 50 years since I wrote serious PDP8 code, I decided to treat this as an exercise to check on my memory (and neuron count). The "solution" by perplexity.ai, posted in a separate thread, looked like an interesting place to start, but as anyone else who gave it more than a cursory glance would have seen, it had many problems, both in terms of syntax and logic. However, after a bit of trial and error, and much reference to a few manuals to bone up on OS/8 - used only for development, not for providing system routine support - I managed to get a fully functional version which I believe meets all of the requirements of the OP.  My experience was back in the paper tape only days, so doing 'raw' I/O was my usual approach. Nevertheless, the comments by Steve Tockey point to some significant and desirable modifications to the original requirement.

Thanks for the challenge.
Geoffrey.