Yes, that was the beauty of the 8 bit era, and many people lost it without even knowing that they lost something very precious. The total control is a very nice feeling.
I'm not sure why "simple, understandable system design" would have to be synonimous with 8-bit computing. One of the most appealing things about new open hardware initiatives is how they bring this simplicity and surveyability together in what's otherwise a very modern design and context.
Seems every time someone applies that to hardware with a wider compute path, other complexity creeps in.
Would be interesting to make a 32 bit Apple 2 style computer. Include a ROM for a means to boot, and leave everything else simple, with some nice slots. Could be a great development / learning machine.
I've "built" such machines in FPGA; PicoRV32 core, hand made display processor, a bit of RAM, and a couple UARTs. It was fun and not that hard for me, a newbie to FPGA.
One of the bigger challenges is integrating peripherals. I got bogged down trying to do SD Card interfacing. There are off the shelf bits of IP from Xilinx, etc. you can use to do this, but that sort of defeats the purpose of the exercise.
I think modern machines started their slide into mind boggling complexity when bus speed and CPU speed outstripped RAM speed. So much complexity and unpredictability is in the all the infrastructure built around cache.
Something like an Amiga or Atari ST was still not hard to understand all/most of, despite being 16/32 bits.
Because once the clock speed gets past a handful of MHz, maintaining good clock distribution and good signal integrity become more painful very, very rapidly.
It's unclear what you're asking for here? The Raspberry Pi Pico and Raspberry Pi Zero are existing and very well documented ARM based single board computers.
Fair enough. I suppose what I'm asking is whether it's possible to purchase a more modern CPU independently of a SOC and design my own single board computer built around that. Can you buy a naked Cortex M0 in a PDIP package? Are there data sheets for it?
A search of the interned didn't turn up what I was looking for, but I'm very new at hardware work. Perhaps newer chips have such tight timing requirements that you can't work with them without using a SOC?
Nearly everything is going to be a SOC because that's what commercial applications need to minimize part count and cost; there's negligible demand for a standalone processor.
If you're just looking to breadboard up a computer but don't want to go back to 8-bit processors, the Motorola MC68000 / MC68008 used in the original Apple Macintosh is a 32-bit processor in a DIP package running at a manageably low frequency and can be found on eBay inexpensively.
