IBM PC-XT Emulator on an ESP8266

Can you run an 8086 PC-XT emulation with 640K RAM, 80×25 CGA composite video and a 1.44MB MS-DOS disk on an ESP12E without additional components?

Yes, you can and I did.

The CPU emulator is a port of Mike Chambers FAKE86.And the composite video is based on the work of Cnlohr and Hrvoje Cavrak

The video is output using DMA I2S and uses only about 10% of the CPU.The components makes a lowpass filter at 7MHz and a correct NTSC CVBS signal.

The video has a resolution of 640×200 and is a subset of the upcoming ESP8266 TVout library.

1MB of the flash is used as a swapfile and creates virtual RAM space to the emulation through a MMU caching system.

The MS-DOS 3.3 1.44 MB bootdisk image is uploaded into the ESP8266 flash and accessed from the emulator as drive A:

It has been tested with MS-DOS 6.22 and works as well.

I used MS-DOS for reference. To not break any copyright you can use a Free-DOS image available here: http://www.fdos.org/bootdisks/

A HDD can be supported through SPI and the SD library.Networking is supported through the ESP8266 Wi-Fi.

I’m using a 3.5″ TFT CBVS display so the text is quite small.A larger CBVS monitor will show a crisper picture.

Once keyboard and mouse code is added, here are 2 of the GUI’s it will run:

Windows 3.0

GEM Desktop

Here is the source code for the ESP8266 PC-XT emulator.

These files are required for compiling it on the Arduino-IDE:

You also need to upload the MS-DOS disk image to the ESP8266 using the ESP Flash Download Tool.

The code outputs video on the I2S data pin (UART-RX) so this needs to be connected to a TV or NTSC composite monitor.

You need to build this circuit to make the output into 1-Vpp CBVS.

Also the filter circuit cannot be connected to the UART-RX pin while uploading.It will make the upload fail.

This just boots the PC up. No keyboard code yet.

Happy hacking your new tiny PC.

11/12/2018 update:

I'm in the process of porting my emulators to the ESP32.

It has better native support for memory and video.