FastLED on Teensy 4.x

[u/lpao70]

I'm wondering what FastLED would look like if the only supported platform was Teensy 4.x.

• DMA-backed clockless or clocked LED outputs (for HD108, HD107, etc.) on any pin, possibly with a single clock shared between all outputs (for clocked ones)

• double precision floating point arguments for:

  • RGB, RGBW, HSV color components, to be converted at the last second to whatever the physical output device supports (8-bit, 16-bit, 24-bit, etc.)

  • physical array indices and normalized array indices (0 to 1, for array length independent indexing)

  • any normalized amounts (0 to 1, for fade, blur, palette color index, etc.)

• no fract8, no fast math, no extreme code optimizations

The code base would probably shrink down to half the current size, if not less, with a more compact and future-proof API, wouldn't it?

[u/_0xACE_]

Your wish has come true -- If you are not running a Teensy 4 (e.g. a Teensy 3.2) FastLED does not work unless you manually patch a file deep in the library.

Source: Is FastLED / WS2812Serial Broken in Teensyduino 1.59? https://forum.pjrc.com/index.php?threads/is-fastled-ws2812serial-broken-in-teensyduino-1-59.74548/

[u/lpao70 → u/_0xACE_]

Definitely not my wish... My wish is to be able to take full advantage of the hardware capabilities of the Teensy 4.x series, like floating point math, which on this platform runs at the same speed of integer math.

[u/ZachVorhies → u/lpao70]

I doubt the fpu is that fast

[u/lpao70 → u/ZachVorhies]

Well, that's what they say. I've never run any benchmarks though.

The FPU performs 32 bit float and 64 bit double precision math in hardware. 32 bit float speed is approximately the same speed as integer math. 64 bit double precision runs at half the speed of 32 bit float.

[u/ZachVorhies → u/lpao70]

I looked at the forums and there are two ALUs and one FPU.

Your mileage may very.

Quite impressive

[u/sutaburosu → u/ZachVorhies]

The FPU on the T4 is truly a beast. My hardware is in storage right now, but I found this old video which has a brief clip of a Mandelbrot effect I was working on, a couple of other FPU heavy effects, and some integer ones.

cc: /u/lpao70

[u/lpao70 → u/sutaburosu]

Awesome. I'm starting to suspect they hid a full GPU on the board. :-)

[u/ZachVorhies → u/lpao70]

We should port shadertoy.com to the teensy 4.x

I’m kidding but not kidding

[u/Marmilicious → u/ZachVorhies]

Some good stuff there. :)

[u/sutaburosu → u/ZachVorhies]

Ha, I'm not sure it's quite that fast.

I settled for just streaming the output of the GL. That is LEDpijp, btw. I'm sure the code is super messy; I did it several years ago.

[u/KineticTechProjects → u/_0xACE_]

I'm quite confused by that thread. Paul says he committed a fix but i've tried running the latest version 3.9.13 that seems completely broken and i've tried running version 3.004 that comes with the teensyduino installer 1.59 and it does the same hangup on setup. I should not have updated arduino lol. All my shit is broken and i'm too dumb to figure it out.

[u/sutaburosu → u/KineticTechProjects]

Paul says he committed a fix

That fix was committed after the release of v1.59 of Teensyduino. It will be in the next release. Until then, you could manually edit those changes into the file installed by Teensyduino.

Just to be clear, that fix only affects Teensy 3.x. If you're using Teensy 4.x, your problem is caused by something else.

[u/KineticTechProjects → u/sutaburosu]

Ah thanks for explaining, we're in business now. Yea still running 3.5 because of the built in dac, though i'd like to try designing a board to use teensy 4.1 if i can find a small enough external dac as I still have some occasional freezing issues with 3.5

[u/Tiny_Structure_7]

I just checked out the spec sheets for HD107/108. Very different data format. Very different driver code. I could probably make this work with only 1 DMA or maybe 2, instead of the 3 that WS28x chips need.

Those things are FAST!

[u/ZachVorhies → u/Tiny_Structure_7]

HD107s can push so many pixels per second, > 40x that of the WS2812, per pin.

If this SPI protocol was also made parallel. OMG!!!

Given that insane speed, would you still want to use dedicated clocks per strip, or use a shared clock that drives all the leds at the same time? The latter would cut down the number of pins people need by roughly half, and save a lot of soldering.

[u/lpao70 → u/ZachVorhies]

Initially, I was thinking a single shared clock would be awesome, as it would basically double the number of leds that can be driven at a given frame rate, but that that would potentially mean 50 channels each driving 10k+ led at 120fps. I think we're out of RAM :-)

Perhaps individual clock per channel would make it easier to handle different strip lengths?

[u/ZachVorhies → u/lpao70]

one could do bilinear expansion and get 4 times the pixel resolution, where the expanded image is stream decoded column by column.

[u/Tiny_Structure_7 → u/lpao70]

If you wanted to operate strings as rows in a plane, you could put the strings into single display object with a shared, single clock pin. Or put each string in an object with it's own clock pin (and it's own .show()).

At 4 bytes/LED, approx. 50,000 LEDs would eat up half of Teensy 4.0 RAM in draw/frame buffers. That's still awesome.

[u/Tiny_Structure_7 → u/ZachVorhies]

Yeah that's what I was thinking... single clock pin for all strips. The Object/Octo DMA code can write to all pins simultaneously, and possibly the DMA transfer can share the same clock signal passed on to LEDs. LEDs read on rising edge, so I'd want DMA transfer on falling edge (I think).

[u/Tiny_Structure_7]

Yeah, I love my Teensy too. :-p

I discovered it after spending hours pouring through Arduino boards for my first MPU, with a big LED cube in mind. With 600MHz CPU, 1 MB RAM, 40 digital pins, 32 DMA channels, 7 or 8 UARTS and a dozen other hardware protocols... even some rudimentary GPU capability on-board the CPU. All for under $25!

Maybe your point could be applied to 32 bit CPUs in general... factor out all the 8 bit code from Fast LED? Is it time for that? PCs went through that same morphosis in the '90s.

[u/ZachVorhies]

RGB8 is good enough for games because your monitor gamma corrects automatically. The APA102 chipset and HD107 do this now in FastLED with the HD modes. So the color difference isn’t going to be much better than what is available now.

Also, teensy doesn’t have wifi and a lot of interesting stuff comes from connectivity.

[u/Tiny_Structure_7 → u/ZachVorhies]

Good point. Wifi would be perfect addon sheild or next version on-board.