Kevin Boone, July 2023
This is a rather silly and pointless program for CP/M that displays a pattern on a set of 8 LEDs similar to that of the 'Knight Rider' car of the 80s TV show (also known as the 'Cylon helmet' pattern). See the included demo.mp4 to see the pattern.
Although it's a trivial application, the program is actually quite complicated, because it uses pulse-width modulation (PWM) of the LEDs to create smooth-looking transitions between patterns.
I wrote this to use with the front panel LEDs of an RC2014 system. Conventionally, these LEDs are at port zero.
Because I couldn't be bothered to create a user interface for so silly a program, the only way to change the output port or the speed of the animation is by editing and rebuilding. All the settings that can usefully be edited are at the start of main.asm.
I wrote this utility to be built on CP/M using the Microsoft Macro80 assembler and Link80 linker. These are available from here:
http://www.retroarchive.org/cpm/lang/m80.com http://www.retroarchive.org/cpm/lang/l80.com
Assemble all the .asm files to produce .rel files, then feed all
the .rel files into the linker. See the Makefile (for Linux) for
the syntax for these commands. There is no make for CP/M, so far as I
know, so building on CP/M is a bit of a tedious process.
Building on Linux is easy, if you have an emulator that can be invoked
from the command line -- just run 'make'. See the Makefile for information
about a suitable emulator.
The brightness of each LED is represented as a number between 0 and 255. These represent that fraction of the time that the LED is switched on, in 255ths. So 255 is fully on, 0 fully off.
In practice, the perceived brightness is very non-linear. There's a big difference between zero and ten, and then correspondingly less difference thereafter. I've picked brightness values that looked nice with my specific front panel LEDs. I've tried with other LEDs, and the results are definitely not as satisfactory.
Apart from the obvious limitation that it's a pointless waste of energy, be aware that this program never quits. You'll need to reset the CPU. I found that checking for keyboard activity made the display jumpy.
For what it's worth, ktrider is copyright (c)2023 Kevin Boone, distributed
under the terms of the GNU Public Licence, v3.0. There is no warranty of
any kind.