Recently I have been working migrating full Atom functionality in an ESP32 microcontroller. This controller is a very powerful and includes 2 cores.
I use a TTVGA PCB that is available for a very friendly price. This has a standard VGA connection, in addition to a PS / 2 keyboard and mouse connection. You can also connect a standard microSD card with version 1.4 and higher of that print.
I've chosen to run the entire VGA control in 1 core and a full Atom kernel in the other core. Both follow their own track: one reads memory and translates it into a VGA image, the other 'only' writes to video memory, without having to worry about the consequences.
I didn't invent or develop very much myself. For the VGA there is a standard library and for the ATOM functionality, I reused the Atomulator. The work is mainly in adapting it so that it works in a microcontroller. Serial.print is my best friend.
An ESP32, like a ESP8266, can host a filesystem (SPIFFS) by default. That behaves as if there is a filesystem available for the programmer. However, its size is limited, due to the actual 4MB size of the ESP32, so it will be replaced later by a library that supports an external SD card. I am using the MMC routines. I installed the Atom Archive on an 8Gb micro SD and it works great.
All graphics modes are supported, including full color support. This emulator is also equipped with scaling routines, so that the full width of the connected screen is used. In order to maintain sufficient speed for the Atom core, a shadow memory is used and it checks whether something has been changed in the relevant video byte. If not, nothing will be recalculated or drawn. Using this approach, even the fastest games can also be played smoothly. Text mode is of course supported and the standard Atom font is re-used to have that great 32x16 capital character screen.
The signals from the PS/2 keyboard are translated into values that correspond to the B000/B001 keyboard matrix to be read. For example, it seems to the Atom as if it has a real Atom keyboard. This way there are some handy tricks possible: on the PS/2 keyboard there are four cursor control keys, on the Atom only 2, where you have to press the shift key for the 2 other movements. The scan code of the PS/2 keyboard is translated into a 'shift' and an 'arrow', so that the ATOM really thinks that these two keys have been pressed. Implementing this routine (which has to be written) was a nice thing: works with an IRQ routine to the ESP32 and had to be '2 cores proof'. Especially vital when writing to the file system. Leared by experience that if the IRQ is not handled ok, the content of the whole file system is lost in space.
Whats next
On one of the next upcoming Atom days in the Netherlands in the post-corona era, I would like to officially hand over a copy to Roland, who is the great inspirator for me and is the leader in the Netherlands to keep the Atom alive.
Not everything is implemented in the Atomulator is also in the ESP32ATOM. For example, I do not a SID or the emulation of image noise or engine sounds lover. So those routines are not implemented. likewise for the BBC roms: I have not implemented the entire BBC basic part.
The source code is of course freely available for those who want it.
Some of you may be are familiar with my FPAtom ROM. That is an upgraded floating point rom which was developed for the ATOMinPC card. In that ROM the floating point arguments were handed over to the Intel x87 core, which has a very fast native instruction set for eg. SQR and SIN. The outcome was redirected to the ATOM and the results were stunning.
On my bucket list is to migrate this functionality to the ESP32 (and the Atomulator), not by native x87, but using standard C fp libraries. Now days these libraries are very efficient, and combining ASM and C is a pain in the neck when it comes to cross platform (as I learned by experience...)
My ultimate goal is to implement these routines in an FPG solution, but that's beyond the scope of this topic..
Leendert
Again a very nice Atom project. I am looking forward to see this in real life and hear and see all the technical details 
