GRG16: Update

Progress on the GRG16!

I decided the next project waypoint for me was going to be an emulator which loads a boot/BIOS rom which will display a 'No cart inserted' message on screen.  This seemed like a good target because it would mean integrating some kind of programming, defining graphics data and enough of the emulator machine itself to display it.

So far, progress has been slow but steady.  I have implemented a rudimentary assembler in Python which can also include raw hex.  The current version can parse/assemble asm code and also extract pixels and/or palettes from images (using the Pillow Python library).  I'm sure there are plenty of bugs still to find in it, but the file it produces passes the quick-scan-in-a-hex-editor test.

I've also made some progress on the emulator side.  In addition to the VPD I worked on previously, the CPU is pretty much implemented, and I've just implemented a BusController to move data between boot/BIOS rom, cartridge, RAM, etc.  It operates in its own little thread, controlled by setting 'registers'.  The part of the CPU which is missing is how to access those registers (and VPD registers) via address maps ($F000 and up).

I strongly suspect I'm going to have to redesign/rewrite a bunch of this stuff as I discover more flaws and bugs.  It will definitely need a bunch more rigorous testing before I do a proper release of it (if it ever gets that far).

At the minute, I see the possibility of making a separate opcode for reading/writing registers on other components, rather than just a memory map.  That should make the emulation quicker as well as increasing the available RAM.  I don't want to suffer from premature optimisation though. :)

So anyway, it seems to be going pretty well, at least as far as producing some kind of tech demo goes. 

Comments

Post a Comment

Popular posts from this blog

Micro:Bit and SPI display

I want to explore the full potential of the BBC Micro:bits my school has. Making rock-paper-scissors games and the like is all well and good, and the students love it (for the most part), but it always feels a little bit gimmicky.  But when students really get engaged and suggest ideas for them (e.g. games, compass display), it all gets a little bit cramped and feels like it could  kinda  work, but not really . Then I found out that all the tiny strips on the edge are actually GPIO pins, not just the fat 0, 1 and 2 ones.  Since then, I've wanted to explore what I can do with it. Hence, over the last few days I have been trying to get the microbit to control a TFT display. I first went for this 2.4" display with a touchscreen.  The SPI interface is just for the microSD, not for the screen but I didn't think that would be a problem because the micro:bit has so many pins.  After much frustration, I discovered that there are many of the pins you can't reliably use extern
Read more

DCS World with TrackIR under Ubuntu

This is a record of my experience of setting this up.  It's meant more as a record for my future self than a tutorial, but maybe somebody will find it useful. 1 - Install DCS First step, install DCS World via the Steam client as normal.  2 - Install LinuxTrack Linuxtrack Download here: https://github.com/uglyDwarf/linuxtrack/wiki/Downloads   Instructions here: https://github.com/uglyDwarf/linuxtrack/wiki/universal-Linuxtrack-package   Using the gui (ltr_gui) requires qt4 libraries, which I could not find in my standard Ubuntu repositories, so I had to use the ppa instructions here: https://ubuntuhandbook.org/index.php/2020/07/install-qt4-ubuntu-20-04 Run ltr_gui from linuxtrack's bin directory to check everything works so far before moving on to get it running under Proton.  3 - Install LinuxTrack into the DCS World prefix NOTE: Attempting to install for Wine games WON'T WORK e.g. here https://github-wiki-see.page/m/uglyDwarf/linuxtrack/wiki/Wine-Games   This is because Ste
Read more

Cardboard Mock-up of USB Joystick

Image
For years now (literally years ), I have been playing around with the idea of making a USB joystick.  You may have seen my previous experiment in building a throttle control . I wanted to use a similar idea to the throttle, taking the angular motion of the handle and magnify it when applying it to the potentiometer.  e.g. move the handle through 45 degrees and the potentiometer gets moved through 90 degrees. I also wanted it anchored at the rear, so I can build a mount to attach it to my computer chair. In the video you can see a cardboard mock-up I made today.  I'm amazed it worked at all, but it even provides a solid foundation for designing the proper plywood one. The process of making a cardboard mock-up was really useful.  There were three fatal flaws in my sketch design which I would not have found out until I tried to make it: Pushing the joystick left/right when it was already pulled full back makes it catch on the rear support. The internal supports in the
Read more