FastLED Library and Hardware SPI

[gfvalvo]

Hi, I have a question about using FastLED library with Teensy. The FastLED web site claims to support hardware SPI with Teensy 3 / 3.1:
https://github.com/FastLED/FastLED/wiki/SPI-Hardware-or-Bit-banging
I would assume (hope) that this extends to other 3.x boards. I tried checking this on a 3.2 board. I used several forms of the ‘FastLED.addLeds’ method:

FastLED.addLeds<DOTSTAR, RGB>(leds, NUM_LEDS);
FastLED.addLeds<DOTSTAR, 11, 13, RGB>(leds, NUM_LEDS);
FastLED.addLeds<DOTSTAR, 7, 14, RGB>(leds, NUM_LEDS);

I then checked the Pin Control Registers for the SPI data and clock pins. In all cases, the MUX field in these registers was set to 3b001. I believe this is the setting for normal GPIO. The Hardware SPI setting for all of these pins is ALT2 (MUX = 3b010). All this leads me to believe that the FastLED library is using Bit-Bang SPI rather than Hardware SPI on (at least) the Teensy 3.2.

Would appreciate it if someone could check my analysis and / or provide their own experience.

Thanks.

 

[PaulStoffregen]

Yes, to software Teensy 3.2 and 3.1 are identical. Programs written for one will run on the other.

Teensy 3.2 has an improved 3.3V regulator and a different bootloader chip, but from a software point of view it's identical.

 

[gfvalvo]

Thanks Paul. So was something wrong my test method, or is FastLED actually using bit-bang SPI on the 3.2?

 

[potatotron]

Thanks Paul. So was something wrong my test method, or is FastLED actually using bit-bang SPI on the 3.2?

I went through the FastLED library at GitHub, https://github.com/FastLED/FastLED

The first part is platform.h, which references the T3.2 at

#elif defined(__MK20DX128__) || defined(__MK20DX256__)
// Include k20/T3 headers
#include "platforms/arm/k20/fastled_arm_k20.h"

which includes this header

#include "fastspi_arm_k20.h"

which is at https://github.com/FastLED/FastLED/blob/master/platforms/arm/k20/fastspi_arm_k20.h

and looks like it's using the hardware SPI to me as long as you use clock_pin 13 or 14, and data_pin 7 or 11 (lines 98 - 127, line 309 - 326).

 

[gfvalvo]

Thanks, never would have found that.