box (OP-1 Clone)

June 18, 2024

Latest:

Oct 28: good progress

• plugins are pretty much figured out
• got audio recording POC done. looking into midi and proper file saving next
• overall doing well. but i think i can go faster

August 27th: progress

The new stack is opengl and tracktion_engine. been making good progress on the audio and graphics. I’m starting to really hate c++. I want to rewrite the whole thing in c or zig but I’m worried that it won’t work and I’ll get stuck.

Jun 18th (2024):

Restarting. Gonna use tracktion_engine for the core audio stuff and write an emulator with ncurses.

Also moving from an hdmi display to pure 128x128 SPI. A lot simpler and also more unique.

Lastly, the pi cm4 is back in stock so I think I’m gonna go with that this time. I had a lot of trouble just getting i2c to work on the radxa, and it’s better in both cost and time to use the pis.

August 16th: PCB DONE!!!!!!!!!!!!!!!!!!!!

• It’s pretty crazy how quickly JLCPCB processes orders

August 9th: PCB almost done

• 
• Close up
• 
• Pretty close on the PCB, gonna order this week I think

July 7th: timeline + new terminal setup

• Kinda busy lately but implemented recording/timeline
• Idk how optimized it is (I feel like I’m checking positions super redundantly + wasting alot of memory)
• Started reading A Tour of C++ by Bjarne Stroustrup, really need to get better at c++

ALSO I got a new terminal setup (copied from jdh)

June 26th: Built box on the radxa zero

• Basically the same process as allolib/allotemplate
• Made me realise that I did a ton of unnecessary setup (linking my own gamma/sndfile libraries for example)
• Pretty cool that it works
• Also got GPIO working
• Once I have an i2c demo done I’m gonna order the PCBs!!!

June 20th: Built allolib on the radxa zero

I decided to build natively instead of cross compiling

• Native compiles literally take >20 minutes
• I think overall the compile time doesn’t matter that much since I only need to rebuild when I add a new library

This actually took me a really long time (~3 weeks)

Ran into a bunch of issues

• No OpenGL support :(
  • I actually started my testing using a Raspberry pi 4 (thanks to the Gaming Warlord Titan Pharaoh Jacob Lin)
  • Raspbian only has support for OpenGL 3.1 for some reason, even though the hardware is capable of 3.2
  • GLFW (windowing system) needs OpenGL 3.2 as a minimum, so it could never create the window
  • I didn’t know about this (or that the radxa zero actually supported 3.2) so buying the radxa was complete luck
• No wifi support for AP6212 chip (wifi/bluetooth module was replaced on the radxa zero due to supply issues, many distributions didn’t have firmware
• Had to flash ~5 times? Manjaro, 3 versions of Armbian, and I also tried starting with ubuntu server and manually downloading a desktop environment
  • eventually succeeded with debian desktop (which actually seems like the most straightforward approach, not sure why I didn’t do it first)

June 6th: HDMI LCD display came!!

There’s still a lot of problems with this design:

• HDMI audio works, but I can’t get pulseAudio (with Gamma) to recognize it as a device
• I bought the wrong display 💀 (so there’s no screws to attach it)
• Lastly, I still haven’t figured out cross compiling

May 16th: Hardware - I2C GPIO Expander

Got my prototype GPIO expander working.

I’m using the CAT9555, an I2C chip with 16 input/output pins.

It communicates over I2C, which is really nice because it only uses 2 pins, SDA and SCL

Additionally, you can chain them together, with up to 8 on the same 2 lines by modifying the I2C address pins, which lets you have up to 128 IO lines with only 2 pins!!!! (8 IC’s should still be within the 3mA limit credit: bluedot

May 4th: Got pixel image rendering working

I’m using allolib’s Image class, which stores images as a vector of uint8_t’s

Every 4 indices represents a pixel’s Red, Green, Blue, and transparency values (stride = 4)

I’m then just iterating through the pixels to plot each one on the screen. You have to iterate in reverse because stb has a different coordinate system than openGL (see below). This means if I draw it regularly, it will actually be flipped upside down. I think the “official” way to fix this is to run:

stbi_set_flip_vertically_on_load(true);

The only thing was, I was worried that it would mess up other texture rendering services (in allolib), so even though it’s more annoying this way, it will probably end up better overall.

I feel like in general the double for loop is a super slow approach, but I’m also not sure how to make it better. The one thing I did think of is to not run plot_pixel() if the pixel has a transparency of 0 (visibility of 0?) because it won’t be visible anyway.

int position = x_position * t_width + y_position;

for (int y=image.height()-1;y>=0;y--) { 
    for (int x=image.width()-1;x>=0;x--) {
    
        int red = get_image_index(x, y, image);
        int green = red + 1;
        int blue = red + 2;
        int a = red + 3;

        if (a!=0) {
            al::Color c (image.array()[red]/255., image.array()[green]/255., image.array()[blue]/255., image.array()[a]/255.);

            plot_pixel(c, x_position - x, y_position - y);
        }
        
    }
}

Here’s how I got the image to be centered, one kind of annoying thing is that I made the MF DOOM head asymmetrical (odd pixel width) when I drew it, so I can’t actually center it. Kinda nice how the integer rounding is actually useful here though!

ALSO note to self: use square images that are multiples of 2^n i.e. 2x2, 4x4, 16x16, 2048x2048 because they are better optimized or something

April 29th: Got pixel drawing working

I’m using the Midpoint circle algorithm to draw circles

Circles are very symmetrical, so you can save a lot of time by just making 1 computation and repeating it 8 times

April 28th: Got wav visuals working

• Also started working on 2d pixel art filter
• I think the basic idea is to render to a frame buffer of the desired size (240 x 160), and make that into a texture.
• Then, you bind the texture to a quad that covers up the entire screen (-1,-1) -> (1,1)

• The upscaling is done with Nearest-Neighbour interpolation, which maintains the sharp lines of the pixel art

• Now I just need to figure out how to do that using the ALlolib system

Art style & Creative direction

• One thing that I was thinking about was that I didn’t want the box to be a carbon copy of the OP-1, so I think I’m going to go with a 2d pixel art style
• I really like the look of this game, Celeste

• It runs at a native resolution of (320 x 180), which is quite comparable to classic retro games

• Here’s a size comparison (from Brandon James Greer)
• Right now my plan is to run a (480 x 320) at 3” or 3.5” display, and then downsample it to (240 x 160). This means every “pixel” will be made up of 4 pixels.
  • I think this gives it enough of a retro look (equivalent to Gameboy Advance), but also gives the freedom to upsample if needed (i.e. wav visuals should be higher resolution)

April 15th: Got the subtractive synthesizer working.

• For now it’s just the basic tutorial one (16 sines and 16 envelopes), but I think it’ll be pretty easy to change the architecture later.
• Also organized the sampler into classes. Side note: Allolib + Gamma is really cool and handles all the complex code so it’s actually really easy to make cool stuff.

I also got started ordering proof of concept parts, and GOD DAMN are SMD breakout boards expensive (Adafruit ones are ~$2.5 each but almost all others are >$7)

April 9th: Got the MPC3000 clone working

April something: starting point

I started working on my new synth, which is a clone of the OP-1 this time.

To start, I was heavily inspired by Prajwal Mahesh’s Portable Synth, as well as the OTTO Project I’m going to try and make updates to this post as I go, as last time it was really annoying to go back and reupdate things.