Saturday, November 9, 2019

RC2019-10 - A102 project - The end of the month of hacking

The short version is that I was super productive on these projects this past month.  I didn't complete it, but I never realistically thought I would be able to.  I lost a week's worth of time, or so, prepping our yearly Halloween Hack (blog post soon)... not to mention losing some time to work on building my Lego Saab 900... (blog post soon too).
One thing I will say, is that by combining the projects together, I tricked my brain into quite effectively "being okay with" working on one project or another, by them all being part of the same project.  So I would say that the month was quite successful.

So Anyway, I'm going to first go through a bunch of goals for the month, for the RC challenge, and in general, and briefly discuss my progress on them at a meta-level.  Then I'll get more into details about the actual work.

Overview and goals

Raspberry Pi / Emulation

I wanted to get the Pi 3 configured and booting right into an emulated  Amiga/Amibian environment.  I got the pi configured with standard raspian instead of Amibian, since I wanted this to be more of a general use machine.  It'd be nice to be able to use it for firmware development of the LL530 as well as the machine that it's targeted for.

So the target changed on this, but it is complete for now.

LL530 Development

I wanted to have the LL530 (USB Interface to Amiga serial keyboards, Amiga/Atari controllers and mice) fully finished.  Although I did not finish the firmware this month, I got more done on the project this month than I had in the past 6 months.  However, I was able to test the DIN pinout to discover that it's backwards, so I need to rev the board for those...

I didn't fully succeed, but I was successful.... if that makes any sense.

RC2014 Integration

I wanted to have an RC2014 Z80 computer built in as well, that I can connect to via serial port, for doing RC dev work without an emulator.  This aspect sadly got the least amount of attention.  I have an RC2014 mini installed, connected to the serial port on the Pi 3.  I've rewired the connection twice now, and I still cannot get it to connect using this wiring.

I spent time focusing on the other aspects.  So... 25% success.

Integration / Battery / Monitor / Enclosure

Most of the effort this past month was in this area.  I wanted to have the entire thing as a finished unit; to be able to be brought to a coffee shop, pull it out, turn it on and use it wirelessly. I can do all of these things right now with it.

So I would say this aspect was completely successful... although It does need improvements, particularly with the screen.

Installing The Linux

I started with a base Raspian image from their site.  I had the Pi hooked up to a HDMI monitor with USB keyboard and mouse.  After using Balena Etcher to get the image onto an SD card, I booted the  machine up.  I went through the basic setup, and updates.

I launched raspi-config from a terminal window, and went through to  enable ssh, i2c, and serial.

Next I installed some useful software packages:

apt-get install screen fs-uae-launcher stella

I made sure that serial was enabled  in /boot/config.txt,


I use screen as my quick and dirty way to connect to the RC2014 which is wired up to the uart on the raspi per the diagram above.  The reset line is wired to GPIO 4, so i use this shell script to "hit the reset button":


import RPi.GPIO as GPIO
import time

print "Resetting the RC2014."

# setup GPIO4 as an output

# send LOW (reset) for 1 second, then restore HIGH (normal run)

print "Done."
# return to high-z state

The Red and Green LEDs are wired to GPIO18 and GPIO12, and I can run this script to do a nice fadey display on them:


import RPi.GPIO as GPIO
import time

red = 18
green = 12


r = GPIO.PWM(red, 100)  # channel=12 frequency=50Hz
g = GPIO.PWM(green, 100)  # channel=12 frequency=50Hz
while 1:
for dc in range(0, 101, 5):

r.ChangeDutyCycle( 100 )
g.ChangeDutyCycle( 0 )
time.sleep( 1 )

for dc in range(100, -1, -5):

r.ChangeDutyCycle( 0 )
g.ChangeDutyCycle( 100 )
time.sleep( 1 )

except KeyboardInterrupt:

I may rewire these, or wire up additional LEDs to the ones specified with the Amibian/UAE led indicators, which are defined as GPIO4 for activity, GPIO16 for "Power", and GPIO16 for a clean shutdown button.

LCD Monitor

For a monitor, I'm using a $10 3.5" composite monitor.  I had to do a few things to get it to work however.

I had to hack the power input so that it would run off of 5v.  These are made to be used in cars, so they expect 12v of power.  At the time I did this, there were examples of doing this modification on
other displays, but not this model.  I powered it up using 12v, then probed the outputs in the power supply section for a 5v rail... and I soldered a 5V input there.

Once I had done this, I connected it to the 5v power in the enclosure, and hooked up the video input from the composite output on the Pi 3.

One snag I hit though, is that it wouldn't work right, It would flash on when the Pi booted, but it wouldn't show the desktop. Testing the Pi with HDMI or a known working composite input worked just fine though.

I was trying all sorts of things, and eventually decided upon trying PAL  video modes instead of NTSC, and that worked.  I spent some time tweaking the overscan settings as well, to stretch the screen to fit.  I also noticed that the contrast viewing range was substantially better on the top side of the display, so I ended up mounting it in the enclosure upside down, and I flip the video in the pi's config too.

So the changes that all this amounts to for /boot/config.txt are:





Although, as you can see from the screenshot above, it's basically unreadable.  So I was able to get it to work, but any future development on this will need to be with a different display.  Something with at least 480 rows, so that Amiga emulation can be reasonable on it.

Combining it all, and the Future...

I spent a few evenings rewiring that keyboard which mostly works really well.  I'm using a 5000mAh battery and get an undetermined-but-better-than-my-old-iBook amount of time with it.

The display is garbage.  I'm currently looking into replacing it with an HDMI-based 4" Waveshare IPS display with an 800x480 resolution for about $40.  Surely that will require moving around hardware inside of this enclosure, and since the display is meant to piggyback on the Pi, I will lose my integration board.

Obviously, I'll need to install the Amiga emulator, Tandy 102 emulator, my Model-T-Shell, and the Arduino IDE so that I can continue development on the LL530

In short, I'm super happy with where things are now, it just needs some tweaks to get it to be usable as a primary system. :D

Saturday, October 12, 2019

RC2019-10 Update 1: A102 Amiga/Tandy/RC2014 Frankenstein

The Enclosure

Since I had started working on this last year, the enclosure is partially completed.  I had removed some plastic ribbing prior to the RetroChallenge, and mounted both a Rasperry Pi 3 and a LL530 keyboard interface board inside of it.  That's about as far as I had gotten last year, so that's a good start. (pics in the next update post)

The Keyboard

I started out with trying to get the keyboard working.  This seems to be the most time consuming portion of the hardware at this point, and has the most question marks associated with it.
The big issue is using the Tandy 102 keyboard with a spare "two header" Amiga 500 keyboard "encoder" board.  I had toyed with the idea of perhaps just wiring up the row/columns to the Tandy keyboard's rows and columns, but this brought up some issues.  Obviously, the matrix would be different... ie; row 2 column 2 would be different keys on the two keybaords.  This would be fine as I could just change the code in the LL530 to convert the fakey-102-500 keycode to be the correct keypress.  I kinda wanted to use the LL530 stock though, so this meant rewiring the 102 keyboard.
The 102 keyboard has diodes at most of the junctions, and there were a different ratio of rows/columns. but I plan on ignoring those by cutting the traces on the board and wiring around them, ignoring them.

I measured resistance for each key on both keyboards.  The Tandy 102 keys ("Alps Mount Round Slider") came out at about 100 ohms when pressed.  The Amiga keys ("Mitsumi KPR Hybrid Switches") were 0 ohms (no resistance).  Could this be an issue with the custom Commodore key matrix scanner on the Amiga encoder board?  Only one way to find out... Wire it up!

I wired up a couple of the Alps keys to the scanner, hooked it up to my LL530 and tried it.  Turns out it all works great, so no worries there! I apparently picked "9" and the left spare key usually between 'left shift' and 'z', which apparently maps to a "section character" (§)

Next, I wanted to try to clean up the keys.  They seem to bind a little as you press them down, as the plastic tube is getting snagged in the mechanism. This is probably due to wear, dirt, etc.  I removed one from the board (four through-hole solder pins), and disassembled it carefully to see what I was dealing with.

The keys popped off using an official key cap removal tool... a pair of tweezers wedged under the key.  Then the plunger and dome could be removed from the enclosure by flexing out the two T shaped tabs on the enclosure top. From left to right: the key cap, top cover (snaps on using the two large T shaped tabs), round plunger, rubber dome with carbonized contact, and finally the enclosure with the contacts in the bottom.

As far as I know, all of the keys are contacting/switching okay, but if i need to replace components, they're easy to swap in or replace the entire key.

I also took this opportunity to replace the "caps lock" and "num lock" keys, which are latching, with two spare keys, since I wanted to reuse the Num key for "right Amiga" and the caps lock key needs to be momentary for the Amiga matrix scanner. The pin layouts were different, so i needed to drill new holes in the board for the momentary switches. The switch labelled "56" above is the replaced caps lock, while "57" is the control key next to it.

Four of the "top row" keys of the 102 keyboard, the arrow keys, don't have quite the right snap/click that the others do, due to 30 years of use and wear.  I happened to have a bunch of exact replacements, which I got on ebay for another project a couple years back, "12x12x7.3mm Tact Switches"

Next is the task of remapping the matrix.  I found some commonalities between the two matrices, seen color coded above... the keys in yellow share the same x/y indexing with the Amiga layout, and the other colors only share the same column.  I traced out the schematic on the keyboard, and cut a bunch of traces.  Next up is rewiring it and wiring it up to the Amiga Encoder board.

More to come....

Wednesday, October 2, 2019

RC2019-10 - The Globbing Of The Projects... Globjects?

Hey.  Long time no post.  How y'all doing?  I'm still here. I've gotten a lot of small things done over the past half year, and a lot of things almost done as well... and some long-standing projects not done too.  So, I've been almost productive...  Anyway, I hope to try something different this month for the RetroChallenge RC2019-10...  Let me explain...

The main projects I've been trying to work on recently are:

LL530 USB interface for Amiga serial keyboards and controllers

I've been poking at it a little over time, and am really damn close to getting the proper firmware done for it, but I just haven't finished it.  Which is stupid because I can actually sell these things once I'm ready!  I have keyboard working for all but my A1000 keyboards, and I have joystick/mouse/paddle working... but not at the same time in a way that I'd be proud of.  I also will eventually need to rev the board to fix three layout issues; a power/ground short, lack of ICSP programming header, and lack of pull-up resistor for VCS paddle sampling.

Llichen-80 Computer (LL80)

Okay, so it's not really a whole other completely new computer... but it is a specific configuration of the RC2014 Z80 computer.  It started out this year as a whole lot of customizations to standard (but old, obsoleted) RC2014 boards to add bank switching, using the 8 bit parallel IO board (the one with all the LEDs and switches!).   Now, I reworked the idea so that I just use the standard "Switching ROM" board and the "64k RAM" board.  That simplifies the design; making it easier to get to the LL80 spec, since just using those two cards replaces two RAM boards, one ROM board, and one IO board... plus no modifications to any of the boards are necessary.

The other part of the LL80 computer is the "LLSuper" board.  This is an arduino-based supervisor of sorts that sits on the serial console port.  It acts as your usb-serial interface for when you use a desktop computer as a console.  This board used a CH376S USB Drive interface to access any flash drive as mass storage (it's a neat part.. like $2 for a board with a USB A port... it talks TTLRS232, SPI or parallel, and handles all of the disk switching, FAT filesystem etc. So there's very little overhead on a tiny ATmega micro.  I also have an I2C based clock chip board for this.  This sits between your console and the RC, and lets you have a kind of shell access to the disk from the console, as well as from the RC.  The RC side of things also got direct access to virtual disk image files with a sector-based interface, as well as direct fileio...

The next steps would have been to write a CPM BIOS and make the thing boot into that.

But I've come to realize that even the LLSuper board is unnecessary.  I can accomplish near-similar things using the standard  "Pi Serial Console" board.  If i use a RasPi Zero, and boot linux on it (or adapt the code in the PiGFX kernel, I can put in my serial-disk IO stuff, for cheaper, without needing to fab up my own board.  I started to mess around with this using my new RC2014 Micro, a Pi Zero, and a slight hack to attach the reset line of the RC to a GPIO of the Pi, so i can now reset the RC from the Pi.

I do have the protocol all worked out for the serial interface using unused ANSI escape codes, which are made for custom purposes like this.

A102 - Portable Emulated Amiga in a Tandy 102 shell

This is one i've wanted to work on since last year. I was trying to get it done before Rochester MakerFaire last November, but burned out on it.  It essentially is a project that joins together a bunch of parts... all of which I have:

  • Raspberry Pi 3, with Amibian... booting right into an emulated Amiga environment
  • Tandy 102 shell, rescued from some unrepairable 102's
  • Tandy 102 keyboard, also rescued (keys bind as they're pressed though)
  • Amiga 500 keyboard interface board, from a long-gone computer
  • My LL530 USB serial keyboard interface board
  • Amiga mouse
  • 3.5" composite LCD panel (new, $10 online!)
  • large Power Bank battery pack
This project entailed hacking the keyboard (removing the wiring/traces on the board) to convert the scan matrix to match an Amiga 500 keyboard.  This gets connected to the LL530, which is plugged into the Pi.  All of it gets jammed into the 102 shell, and becomes a portable computer. 

I waffled a bit on this... mainly because the keyboard stuff would be a chore.  I want to remove every key, and clean their travel tubes, to eliminate the keys binding.  Wiping out the traces and rewiring the board seems like it's going to be a tedious process... So i kept thinking that maybe I should make a cherry-mx switch based board to fit the keyboard space instead... and... yeah... i just kept going down that same path of "maybe i should do this other thing" instead... instead of actually moving forward on any of it.

I also pondered putting the entire Llichen 80 computer into this shell... which brings us to...


So that's where RC2019-10 comes in.  Why almost fail at three projects when I can almost fail at ONE project! Seems a lot more efficient!

The end result for this month will be to have a working portable laptop computer that runs Amibian (Linux), RC2014 (via serial connection to the Pi) and general Linuxy stuff.

Or, more granularly, here are the tasks as I see them now: (in no particular order)

  • Finish the Keyboard + Joystick/Mouse firmware for the LL530
  • remove the wires on the 102 keyboard PCB
  • clean the travel tubes on the keyboard
  • rewire the keyboard to match the Amiga's matrix
  • Wire the keyboard to the Amiga 500 interface board
  • Connect the RC2014 Micro via the Pi's serial interface pins
  • Additional buttons on the device to cleanly shut it all down
  • Have it all powered from a 5V/USB powerbank mounted internally
  • Serial-console textmode app for Linux that provides the beginnings of a backchannel to 
Stretch goals:
  • Full drive interface for the RC2014
  • CP/M BIOS for the RC2014 that uses the serial protocol
  • Fit the RC2014 Mini + 64k RAM + switching ROM + TMS9918A cards inside the case
  • Have the video switchable between the Pi and the TMS9918A video card

Not sure how far i'll get, but it globs together all of the recent projects in a way that I won't feel like I'm neglecting one project by working on the others... since they're all the same project now. :D

Thursday, March 21, 2019

Llichen-80 (Retrochallenge 2019-03 Update)

I had originally intended for any time I could devote this month to the 2019-03 Retro Challenge was going to be for a new version of my RC2014 Z80 computer emulator, adding support for the TMS9918A video display chip.  But my plans have changed.  With the recent advancements with The 8-bit Guy's "Commander X16" 6502 computer, I decided to start reviving a project I was considering for a while.  The great thing is that there's so many aspects to it that it's like a grab-bag of things to do.

The original idea was to sit down with a C64, floppy drive, monitor, joystick, mouse and reference books, and start with BASIC, writing a text editor, assembler, IDE, etc and work my way up to having a windowed operating system like GEOS with a few utilities and such.

Except now, the spec of the system is designed by me, and I'm building that too.... Which meshes in perfectly with my original intention to build a RC2014+TMS9918 emulator, which I can use for initial development, and kickstarting the boot rom onto it.


I wanted some sort of related name for the project, so I was thinking Llama, TMS, which became Llitmus, like the PH sensitive dye.  I was gonna go with Llitmus-80 with the '80' because it uses a z80, but then once I read that the litmus was made from lichen, I just went with the name Llichen-80.

First, let's get into the Llichen-80 system specification.

  • RC2014 backplane/base system
  • 7.37 MHz clock speed
  • 32k RAM from 8000-FFFF
  • 8k BASIC ROM from 0000-1FFF (*)
  • 32k RAM from 0000-7FFF (*)
  • Digital IO board at port 00
  • TMS 9918A video board at port 10,11
  • ACIA Serial port at 80
  • ACIA Serial port 2 at C0 - connected to CH376S USB drive interface
So (*) Indicates something... there's an overlap of these two items. My existing design piggybacks bit 0 of the output from the digital board to select which of the two of these that memory READs come from.  That is to say that writing 0x00 to the digital out board will select ROM, and 0x01 will select RAM.  Writes to these locations always go to RAM.  So one way I can test this is:
  • Start up the computer
  • select ROM bank
  • Write a basic program to peek from the ROM and write to the RAM
  • select the RAM bank
  • Yank out the ROM board, and everything still works fine
10 OUT 0,0
20 FOR A=0 TO 8192
30 B = PEEK(A)
40 POKE( A, B)
60 OUT 0,1
This all works great!  One addition I made was to intercept the VCC to the RAM chip and have it also connected to some CR2032 batteries for a backup.  It's not perfect, but it works well enough for my system for now.  I also added a switch to force the use of the ROM, since sometimes the bank switching can get into a messed up state and you need to force reboot off of the ROM.

The other thing I created was a second ACIA serial port, essentially duplicating the circuit of the stock ACIA serial port, but changing it to look at ports C0 and C1 instead of 80 and 81.

The TMS could be configured for anywhere, for the most part, but the ACIA chip IO port mapping is messy so they consume essentially from 80 to FF.  I went with the SORD-M5 configuration of putting it at 10 and 11h.  Although there might be issues with this...

Anyway, more about these modifications and such at the end of the month.


I ended up reassembling my RC2014 system, and started working on testing out the configuration.  I Was able to write a few BASIC programs to output to the video chip and to a TV I had hooked up, as you can see in the photo above.  I was noticing some weirdness though. The LEDs on the IO board were flickering when I was doing writes to the TMS, so I may need to move the port around to another location. I think I'm gonna go with the MSX setting of 98 and 99h.

I also became very aware that I do not yet understand how to get the chip to do what I want.


I was going to write the emulator using QT Creator for maximum portability, and also using the Z80 emulation core and frameworks I created for my existing RC2014 emulators.  But recently, after thinking about it for a little bit, I realizes that 90% or the emulator I need is already out there and already very well supported.  MSX.

There was really no need to get a whole video display system working with my existing emulator when I could start with an existing, debugged, well supported emulator, openMSX, and just create a new hardware profile for the RC2014 with my system's configuration... and with some changes to support my bank switching hardware and such.

I made a branch of openMSX on github to handle any/all of the changes I've made for it, which at the moment is just getting it to build on OSX/Darwin 10.14 correctly.

I also was messing around with my good old friend, the Texas Instruments TI-99/4A as it uses the TMS9918 chip. I figured that I could experiment around with how color and graphics look.  I'm not a fan of the TI's font, nor the MSX's font for that matter, but I figured it's a good platform to get reacquainted with the weirdness of the TMS and to see how this all might look in the future, perhaps.

This is of course just a screenshot from the impressive web-javascript TI emulator at

More as it develops...

Friday, September 28, 2018

More Laserdisc Stuff! A wild Pioneer CLD-V2400 appears!

I just picked up this Pioneer CLD-V2400 in full working order, and in excellent condition.  It was made in 1993, around the same vintage as my Pioneer CLD-S201... but with one major difference... a SERIAL PORT!

It's missing a couple of the more "industrial" commands that allow it to seek quickly (+/- 100 frames) without noticeable glitches/squelching.. so it's not ideal for laserdisc video games, which were crafted so that you could play a game non sequentially without seeing pauses as the disc seeks.  I guess it's able to move the head super quickly within the VBLANK section of the disk

I'm getting ahead of myself...

This thing has a DB-15 connector On the back for the RS-232 serial interface, which includes TTL Serial (0-5v) and RS-232 serial (+/- 12v).

Since I couldn't find my USB-Serial interface, I tried making a TTL cable, and connecting that via FTDI cable to my Mac... I wasn't able to get it to reliably work. I think it might be a that the FTDI/Mac combo couldn't do the 4800 baud rate or something.

Instead I made a DB15-DB9 Null modem cable, and decided to plug it into the 9 pin serial port on... something?

I had a hard time finding any of my machines with DB9 serial, but eventually remembered that my tiny Toshiba Libretto 50 has one! So yeah! Windows 98 and HyperTerminal it is... and it worked great!

Next, I went through the V2400/V2600 manual, (and the V4400 manual) to figure out some commands that I could do.

I had some experiments I wanted to do with using the "user area" of the on screen text of the player.

First of all, I wanted to see how to do it.. which you can see in this pic.  I had my CAV Duran Duran disc playing, obviously.

My thought is that I can do thing similar to the "Rollercoaster" project and just command the thing to play scenes, but it can be taken a step further.

Another option available is to get a user number press from the remote.  The user presses 0..9 and you get that back through the serial port.

It would be possible to make a modern game or interactive video thing using onscreen text for the output, and remote for the input.

The display area on this player is 10 lines of 20 characters each.  Not a lot, but enough for activities.

Perhaps I could encapsulate the game and logic inside of an Arduino would work... but that still brings up the TTL serial issue.

I scoured my basement, looking for my Belkin USB-Serial dongle, which I'm starting to believe I never actually had... I eventually gave up and decided to kludge together this monstrosity.

The nice serial cable I made was a null-modem cable, but the serial level interface (blue board) had the wrong gender and pins for my use, so i tacked on some wires to the correct connector.

The Arduino is a Pro Micro (ATmega 32u4/"Leonardo") made for another project. so it already had the microSD socket and external FTDI connector for a serial peripheral, so this went together substantially quicker than looking for the USB interface.

Regardless, this somehow worked... really well.  I needed to make a simple Arduino program that just reads in from "Serial" port, the USB side of the Leonardo and writes to the "Serial1" port, which is on pins D0 and D1.

The trick was to have both open at 4800 baud.  I had the LD side at 4800 baud, and the USB side at 115200, but that didn't work.

I've made it so I can type on my mac, and control the player... or have the Arduino autonomously control the player.

One of the things you can monkey with is disabling the squelch of the video and audio.  This is what blanks/blues the screen and mutes the audio while seeking, or while doing pause in CLV mode.  When it's off, you can play multispeed/stillframe with audio, stillframe on CLV (which doesn't really work, but it's neat!) and do chapter seeks while still seeing the content.  It's really fun to mess around with...

I think I need to make a script that seeks to the end of the disc to get the duration, then randomly seeks around, plays a second or two, and then repeats that... Especially with squelch off!

Tuesday, August 14, 2018

Commanding Laserdiscs

Coming soon...
For the past couple evenings, I've been poking at controlling video playback programmatically... I was inspired by Kevin Savetz' recent project to resurrect the Rollercoaster Apple ][ Laserdisc game.  He got it working, fixed it, enhanced it to work for the DVD version of the game, and was showing it off at KansasFest.

My first quick hack, as seen before on this blog, was to screen-scrape an Infocom game (Hitchhiker's Guide to the Galaxy), and based on text from that, force VLC to play back certain frames or tracks of video from the Hitchhiker's Guide TV show.

I've been poking at actually making Rollercoster be playable inside the browser for my next trick. I'm basing it all on the source code, which Kevin has made available to us, and using a HD transfer of the movie, which hopefully is the same edit of the film as the Discovision Laserdisc.

There will be more on this later, but the short version is that I'm using jsbasic to run Applesoft Basic right in the browser (no emulation of an Apple ][ ), simulating the Super Serial port (6551 ACIA chip), capturing the BASIC game's laserdisc commands being sent to said serial port, and then using that information to control a fakeo-laserdisc player, which is just an HTML 5 video player.  I'm still working through all of this.  The cool thing is that when I'm done with this, it could be a great test system for people wanting to make more LD-AppleII games.  As long as you use video files that can be properly frame-associated with real discs, it should be a drop-in kind of thing.

NOTE: if I learn more information, I'll note it in this post.  I'm really green when it comes to Apple II hardware, and really Apple II programming in general. This is really my first deep-dive into Apple II serial hardware and specifics of Applesoft BASIC!

Super Serial card

The Super Serial for this game is in slot 2, and is fitted with a 6551 ACIA serial interface chip. Writes to the ACIA get sent out immediately, they are not buffered.  The ACIA has one bit on its status port 0x08 or b00001000 that goes high when there's a byte to read.  The LDP will send a 'R' when its current task is complete.

The Super Serial card, being in slot 2 means that its four registers are at decimal locations:

  • 49320 - Data 
    • Read from here to read characters sent to the Apple
    • Write to this to send out characters to the LDP
  • 49321 - Status
    • Read from here to get error codes, 
    • Read and mask off 0x08 to get the "is a character ready to be read from the LDP?
  • 49322 - Command
  • 49323 - Control
    • These two are used to configure the port, for baud rate, parity, etc.  For this project, I'm simulating the behavior of the device at a very high level, so i basically ignore all of this stuff.
    • The real hardware runs at 4800 baud, 8-N-1
This means that to write a character (newline) out to the LDP:
  • POKE 49320,13

LDP Simulation

Anyway. there's been some interest in others wanting to simulate the Laserdisc player (LDP) using other methods (using VLC for example), so I thought I'd just do a quick post to explain my current understanding of the specific commands used by the game. You can look up specifics of the protocol in the LD-V4400 User's Manual, or in the DVD-V8000 User's Manual  All commands are two-letter sequences, uppercase (although the manual says that it accepts lowercase as well.) and can have a number BEFORE the opcode.

There are a lot of commands that these can handle, but these are the commands that we care about for this game:

Go into "frame mode".  This means that any addresses will be in number of frames from the start of the disc.  Frame 0 is the first frame on the disc, the final frame is dependent on the duration of the disc.  CAV discs are about 30 minutes of content. at 29.97FPS (NTSC), that is roughly 54,000 frames.

(address) SE
Seek to the address (frame number) and go into still-frame mode.  Reading from the ACIA, 

(address) PL
Play, and go to still-frame mode when the address (frame number) is reached.

Additionally, the game's command strings use '/' to indicate a carriage return (CR) character, which is sent as decimal value 13.  The player will then execute the command, and will send back an "R" character (decimal 82) when it completes.

Let's go through a couple real examples...

  • Switch the LDP into frame mode
  • Seek to frame 2818, and still-frame there
  • LDP will send "R" when it has completed.
AKA: Still frame on frame 2818, will send "R" when done.

  • Switch the LDP into frame mode
  • From the current position, play until the frame number reaches 2134, and still-frame there
  • LDP will send an "R" when it has completed
AKA: Play until frame 2134, will send "R" when it reaches there.

  • Switch the LDP into frame mode
  • Seek to frame 6726, and stillframe
  • LDP will send "R" when ready
  • (switch to frame mode)
  • Play until frame 6959, and then stillframe
  • LDP will send "R" when ready
AKA: Play from frame 6726 through 6959, send "R" when done.

Game implementations

The serial port configuration and setup is at line 31000.  The sequence it does is that it POKEs 11 to 49322, and 28 to 49323, which sets up the serial port configuration (baud, parity, etc).  It also does something with CHR$(4); "PR#2" or "PR#0".  I'm honestly not entirely sure what those are for, something with sending data to the serial card.

The BASIC code to send the command strings is at line 40000, and the command string is stored in VC$.  So in the program you'll see stuff like:
34000 VC$ = "FR2818SE/": GOSUB 40000 
34011 VC$ = "FR6726SE/FR6959PL/": GOSUB 40000
You already know what these do from the above examples!

The LDP communication code at 40000 is:
40020  FOR I = 1 TO  LEN (VC$)
40030  IF  MID$ (VC$,I,1) = "/" THEN  POKE 49320,13: WAIT 49321,8:J =  PEEK (49320): GOTO 40060
40040  POKE 49320, ASC ( MID$ (VC$,I,1))
40060  NEXT I
40070  RETURN
Or, in human readable terms:
  • if "DISC" is set 0, then there's no VDP, so just return
  • For each character of the command string:
    • if the character is a '/', then send the VDP a carriage return, and wait for "R" response
    • otherwise just send the current command string character to the VDP

The code also uses the "WAIT" command, which was not implemented in the javascript library I was using.  This command essentially blocks, and waits until the conditions are met.  In the above code it essentially is PEEKing at 49321 (ACIA status) for bit 8 to be set; for a character to be ready to read in.. It then reads the character to variable J, which is then ignored. ;)  But it knows the LDP is done with the task.

Friday, August 10, 2018

4 Hour Projects: Adding Video to Interactive Fiction


After listening to the Eaten By A Grue podcast:19 about the interactive laserdisc-based game for the movie "Rollercoaster", and then following that up with the episode about Hitchhiker's Guide:16, a spark popped in my head. It should be possible to somehow "watch" the Hitchhiker's Guide (H2G2) Infocom game and play clips of the TV show, movie, etc, syncronized to the scenes and what you're looking at.
All of the distributable code for this is available at the github page for the project.
Just about all of this project is based on existing stuff, but I glued it all together.
  • Frotz - runs the Z-code, in a text-based terminal
  • VLC media Player - plays back the video
  • H2G2 TV on DVD - the DVDs
  • Netcat - so my client can talk to the server
  • Tee - to split the output from frotz
  • Perl script (in this repo) - "reads" the text, matches text, tells VLC what to play
The whole thing kinda works, is buggy, unoptimized, but that's the nature of a 4 hour hack.


This is the basic system... This was a quick sketch I made to get the idea down. Essentially there are two halves. (I also called it "zvid" instead of "llifvid". pls ign. thx.)

Server/Video player

The server on the left is essentially a perl script that:
  • Matches text from the interactive fiction
  • has a simple interpreted language that can perform sequential functions
  • outputs "remote" commands for VLC
The output of that perl script is piped into VLC. If you're going to reproduce this, be aware that enabling the VLC shell it was a bit tricky, and I didn't document the process. I think I needed to enable extended preferences in VLC to see the bit to turn on that feature.
Also on this side are the video files for H2G2 episodes 1 and 2. I used Handbrake to decode them off of my DVDs. I do know that the episodes exist online, but those may be set up for web streaming, and will need to be transcoded via handbrake or some other tool. It basically just needs to add some information in that isn't there.
Netcat (nc) is setup as a listener for the text output from the game engine. That is piped into the perl script, whose output is piped into VLC.

Client/Game engine

The client on the right is some bash script piping and connection of Frotz with the game file. I used the ms-dos version of the data file, although I do not know if any other versions differ in any way. This was just easiest for me to grab without digging out and setting up my Amiga to pull the files off of my game's floppy.
The output of frotz is piped through tee. Tee takes the output and splits it to two different places. First, is the console so you can see what you're doing, but it also usually saves it to a file. I've changed that path to be piping the output to netcat, setup as a transmitter to the server.


In the perl script is a quick interpreter that I hacked together to run little micro scripts of code. I started doing this as an array of arrays, but if you've ever done that in perl, you'd know that such things are never good ideas in that language. I briefly considered hopping over to python to do it, but I already had stuff done, and was still toying with the idea of having the perl script itself listening to a socket, which i was unsure of how to do in python. So it's in perl.
Anyway, I switched it over to be a plain text blob in the source file. At startup, it cleans up the text, removing comments, and empty lines. It also breaks it up as two elements per line; the opcode and the parameter, and store that as the runtime program. This vastly simplified runtime routines.
The two main entry bits for the language are the label and the text match. It's sort of event driven, sequential language, with no nesting, no calls, no iterations, none of that... one operation per line. I did include comments though which are denoted by pound sign, # and continue to the end of the line. They can be put anywhere, as they are filtered out before runtime.
: label
Labels are used for 'goto' statements, or calling the goto function to set the current PC (program counter). If you call the doGoto() function, it will adjust the PC to the line after that label, or to -1, indicating that it was not found, and there's nothing to do.
? text to match
This denotes text that should be matched. As the program runs, it reads in byte by byte from the client and accumulates it. When it hits a newline 0x0d, or 0x0a, it sends the accumulated text to the "got a line" function. That one tries to match each "text to match" string to see if it matches any part of the current line. If it does, it sets the PC to the next line, and returns.
From there, there are a few opcodes that can be called:
seek 100
This will seek the current video file to 100 seconds in.
until 110
This will wait until the timer hits 110 seconds in in the video. Due to limitations of time, this is implemented as a hack. Instead of looking at the video file to get the time, it remembers the last 'seek' number called, does a difference, and sleeps for that many seconds, blocking. For the above two codes the "until 110" call will essentially sleep for 10 seconds
Indicates that a sequence of opcodes is done. "do until done" will stop here" this leaves the PC at -1, indicating it's done.
player play
This sends the "play" command to VLC. It can send anything. Useful things are:
play    # press play on the current videopause   # toggle pause!frame   # advance one frame. forces a paused statestop    # stops the playerfullscreen on  # makes the video full screen (on|off)seek 100 # you can manuall call this as wellrate 2   # twice speed... or "0.25" for quarter speed. etcadd FILENAME   # adds a file to the playlist, and switches to it
These essentially just print out the command, as the VLC shell is consuming the commands directly.

Determining match strings

For this I basically ran "frotz hhg.z3" and copy-pasted long lines of text from the game to match that seemed unique. It worked okay but was kinda tedious.
I was originally going to extract out the room names/descriptions from the z3 files using the tools, but gave up on that for this simpler, quicker approach.

Determining timing

So to get the second counts, I ran VLC, playing the video file, directly: "vlc episode1.m4v", and did a lot of typing in the shell of the above commands. I would type "play" to let it play, then "pause" or "frame" to get it to stop. You can get the current time with "get_time", manually seek to specific times like "seek 300" or differences from the current time, "seek -10" for ten seconds ago, etc.
I could use the GUI for this, but it shows time as mm:ss rathe than time as seconds only.
It was tedious, but it worked. An easier to use mechanism for this would be advantageous.


So yeah... it worked.  With a lot more work it could be made to be reliable, have a nice editor, and be easily streamlined into more games.  I'd personally want to see an integrated executable as well, to get rid of all of this netcat and shell weirdness, and just have one exe that runs, reading in a language file.  Game packages could be created with the language file, audio, video, etc.  But I feel like I've accomplished what I wanted to for this.