So, about the parallel port emulation problem. With all the complexity for full parallel port support on PCs requiring a PCI card, surely you could do full parallel port support on Raspberry Pi by the use of the GPIO, I2C, or SPI, correct? Indeed, you can, and I found one such project, but you have to do a bit of searching before you get there.
20180820/DuckDuckGo ecp port on raspberry pi
20180820/https://www.reddit.com/r/raspberry_pi/comments/4f5ltd/gpio_to_lpt_is_it_possible/
Here is an interface for Arduino control over CNC mills, etc. connected via a parallel port.
20180820/http://www.coreforge.com/blog/2014/08/grbl-tb6560-interface/
20180820/DuckDuckGo raspberry pi parallel port
Ah ha! Here it is. Full support for ECP in version 2, i.e. IEEE 1284 bi-directional.
20180820/https://github.com/garlick/pi-parport
20180820/https://en.wikipedia.org/wiki/Parallel_port
So, let me summarize the whole parallel port ordeal this way. In the early days of computers, if you wanted a cheap, low-level electrical control interface, you would head straight toward writing a program on your MS-DOS PC that manipulated the parallel port by a custom pattern. For a short period of time, you could also do likewise even on a more powerful computer running a multitasking operating system like Windows 95/98/95SE. But, nowadays, parallel ports are all but obsolete for modern applications. By far and large, specialized hardware is connected to modern powerful computers only through a “serial port” discipline. If, by contrast, you want to be able have some semblance of lower-level hardware control from a powerful computer in the modern era, you would head straight toward a Raspberry Pi and program the GPIO pins, which will give you an experience similar to Windows 9x. If you want really low-level control on a real-time system similar to MS-DOS, you would head straight toward programming an Arduino microcontroller.
Wow, that is really interesting, when you think about it. The older PCs? We never really retired the hardware, but rather we assigned new names for feature-equivalent computers. For the new computers that were the same physical size as the old ones, they took on the same name as the old ones. At the same time, the desired applications on those computers changed to adapt to the new applications available. Old-fashioned MS-DOS computers became microcontrollers. Old-fashioned Windows 9x computers became single-board computers.
But now, and this is where things get really interesting. What about the latest PCs, you ask? Well, those kind of fell off an edge of a cliff of a sort. What happened was that yes, those machines continued to gain new features and functions. But consumer mass market computer users were no longer interested to keep using the new computers! The new features and functions simply just weren’t interesting compared to what older computers could already do. The line stopped at laptops running Windows XP Media Center Edition: right in the midst of 2005, when laptops were on their upwards trajectory of replacing PCs in terms of mass market share, and laptops have also long but ditched some of the low-level hardware fancies from PCs of times past such as parallel ports and floppy disk drives. Also, these laptops added new Wi-Fi wireless communications network support, which proved to be massively popular. The result? The consumer mass market polarized itself around smartphones, tablet computers, and laptops. Docking stations are available for these smaller computers should you want to have a larger monitor, better keyboard, and mouse for your computer, but most people were no longer interested in connecting those peripherals to a full-sized desktop PC. The smaller computers provided enough features and functions for most people, so why pay for the larger one?
Desktop PCs, nowadays, are only used for computationally intensive, real-time interactive computing such as the latest video games, three-dimensional design, and real-time simulations. Nowadays, non-realtime computationally intensive computing is outsourced to cloud computing and accessed via a mobile device: laptop, tablet, or smartphone.
Again, I reiterate, because this is important! Why are the biggest most expensive computers “required” for video games? They are “required” because the commercial video game market, where people are willing to pay a considerable amount of money for their video games, is by far and large inhabited only by people who already paid a considerable amount of money for their computers. Now, this shouldn’t be surprising, but if someone starts out on on foot by buying a cheap computer, chances are likely that they’re going to want to keep the price of complementary products down too. Yet this means that one cannot fund an expensive video game with even a million of these such customers: chances are likely that people are willing to pay even less for their software than they paid for their computer hardware.