trylle / ibm515x Goto Github PK

Hi,

This is a really cool project and I am excited to build it and test it out on my CGA monitor. I am sure you have moved on from this to new pursuits, but can't help but ask a few things.

1. On the temporal dithering, one thing that I have noticed when doing that (on a Tandy and on tweaked CGA) is that if you take the resulting image and swap every other line you get a consistent brightness across both images and it helps flicker a lot. https://www.youtube.com/watch?v=MR1uq4y9G34 The picture is true to life, it doesn't flicker a lot. Certainly, it is there.
2. Have you thought about making the display 640x400 interlaced video? Not sure if 640x480 might work as well? Not sure how awful or full of flicker it will be, but would be neat. The ATI VGA Wonder will allow you to display 640x350 using some kind of process to get more colors on the monitor (and it does) but not sure if it is temporal or something else.
3. Last one, do you think you could overmodulate the signal to get more colors in 60 Hz? So, we have 16 levels of TTL, what if you were to drive the signal FASTER than the actual rate the pixel changed using PWM. So, if you are able to drive a 15.75 KHz signal and you could drive a signal at 4 times that at 63 KHz then I think during the pixel draw portion of the signal you could switch it faster than the raster scan and drive more than one color per pixel. At 4X you could drive Red-Black-Black-Black and probably get a darker red, or Blue, Blue, White, Red and get a light magenta. Odd combinations like Brown, Cyan, Red, Yellow would give even additional colors. I think the math works out to with 16 colors and 4 "cycles" per pixel you could get 3,876 combinations. If you could do 8 cycles per pixel that would require precision control of a 126 KHz signal that would give you 490,314 combinations. 12 "cycles" per pixel would be 17.4M colors which has to have every color close to 24 bit. 12 would require precision control of a 189 KHz signal. I don't know how the TTL to Analog RGB circuitry inside the 5153 would handle the frequency though or if it would switch fast enough. Anyway, if you read this far this is what your project made me think of.

Regardless, 640x400x17M colors on a TTL CGA monitor would be something to see for sure.

I was absolutely stoked to find this project! I have an IBM 5153 and am planning an art installation that uses it to display an interactive video. I've looked at other VGA to CGA options and this one seems the most desirable for the monitor I'll be using. I'm new to using a Raspberry Pi for something like this and could use some pointers on how to properly implement it.

1. For the timing breakout board, is the IC you're using a 74AHCT125 quad-level shifter? The link to Benjamin Gould's page is dead. Any more information on the circuit you built would be appreciated.
2. Can this be used to play video directly from a Raspberry Pi or is it streaming from another source? Is there a means for me to play a video through the Raspberry Pi itself? If so, what are the limitations for doing so?

Any advice would be deeply appreciated.

Here are the photos of our (mine & @bertronika's) setup and results so far (RPi desktop shows and one can use it, also the dpi/fb_render_test works; have not tested netvid/streaming/dithering yet!):
https://imgur.com/a/e6RcodQ

Hardware

• To buy/obtain: Raspberry Pi 3, 2x SN74AHCT125N chip, 6 resistors, protoboard, jumper wires
• Can use jumper wires to directly interface the male CGA connector
• We will provide schematics ASAP!
• Our goal is to run a Dosbox application just like it would show on the original IBM PC (or PC XT) with CGA graphics

Software
Complete instructions for fresh RPi install + latest Chrome + VirtualXT emulator in browser.
Since the resolution is 1920x200, normal Dosbox software doesn't properly render, thus the easiest "hack" for this was to use an emulator in browser and stretch it to fill screen. We use old Raspbian version from the time of this project to avoid incompatibilities.

• Flash .img from https://downloads.raspberrypi.org/raspbian/images/raspbian-2017-09-08/2017-09-07-raspbian-stretch.zip
• Put ssh and wpa_supplicant.conf on /boot

sudo apt update (apt upgrade not needed if just doing basic stuff!)
sudo apt install snapd
sudo reboot
sudo snap install core
sudo snap install chromium

git clone https://github.com/trylle/ibm515x
cd ibm515x/configs
dtc -@ -I dts -O dtb -o cga.dtbo cga.dts
sudo cp cga.dtbo /boot/overlays/

• Edit ibm515x/configs/config.txt and add line avoid_warnings=1
sudo cp config.txt /boot

• Edit ibm515x/configs/cmdline.txt and change root=/dev/mmcblk0p7 to root=/dev/mmcblk0p2
sudo cp cmdline.txt /boot

• Edit /etc/lightdm/lightdm.conf and set under [Seat:*] (not before!):
  xserver-command=X -s 0 -p 0 -dpms -nocursor

sudo apt install apache2

• Copy virtualxt to /var/www/html/virtualxt (see section below!)
• Add line to /etc/mime.types: application/wasm wasm
• Remove the only line in /etc/ld.so.preload
• Create /home/pi/virtualxt.sh with contents, then do chmod +x virtualxt.sh:
  /snap/bin/chromium --kiosk --app="http://localhost/virtualxt/?activity=0&touch=0"
• Replace file /home/pi/.config/lxsession/LXDE-pi/autostart contents with this line:
  /home/pi/virtualxt.sh

sudo reboot

• To build project binaries (OPTIONAL - we did NOT use this for our project and couldn't get streaming to work):

git clone https://github.com/trylle/ibm515x
cd ibm515x/
git clone https://github.com/trylle/netvid
sudo apt-get install cmake libblkid-dev e2fslibs-dev libboost-all-dev libaudit-dev libeigen3-dev
cmake .
make

VirtualXT

• Obtain the following files: (Copyright (c) 2019-2023 Andreas T Jonsson [email protected])

https://app.virtualxt.org/index.html
https://app.virtualxt.org/freedos_web_hd.img
https://app.virtualxt.org/script.js
https://app.virtualxt.org/virtualxt.wasm

• In index.html change
  <body style="background-color:black;">
  to
  <body style="background-color:black; margin:0px; padding:0px; overflow:hidden;">

• In script.js change
  canvas.style.setProperty("transform", "matrix(" + xScale + ",0,0," + (xScale * yScale) + "," + transX + ",0)");
  to
  canvas.style.setProperty("scale", (document.body.clientWidth / width) + " " + (window.innerHeight / height));

• Edit the hard disk image (freedos_web_hd.img) as you see fit.
  Tip: DiskExplorer works great for editing - use the profile "vmware plain disk"