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Why GPIOD_PDIR becomes 255 as soon as pins PTD0-PTD7 (PORTD0-7) become input?? Should not that be 0? for Teensy 3.2 GPIOD_PDIR becomes 0 for Teensy 3.6 GPIOD_PDIR becomes 255 Code const byte D0 = 2; const byte D1 = 14; const byte D2 = 7; const byte D3 = 8; const byte D4...

@Frank B, Yeap you are right. I need to read a few 8-bit values (from 8 GPIO pins) as fast as possible (e.g. 24 Mhz) & save in memory & process :)

@UhClem : Thanks for the tip! @Frank B (#21): Actually I am not really interested in pin toggling, but more on how fast I can read GPIO (e.g. how speedy digitalReadFast() is). I just thought that the ring oscillator would be a quick example to test GPIO speed across various platforms. @Paul...

If I am correct GPIO access is at F_CPU speed, not F_BUS speed ... (If i recall right)

@ defragster I use Teensy 3.1 @ 96 Mhz, just like as Frank B (Teensy 3.2 @ 96 Mhz) CPU is T_3.1/3.2 F_CPU =96000000 ARDUINO =10801 F_PLL =96000000 F_BUS =48000000 F_MEM =24000000 NVIC_NUM_INTERRUPTS =95 DMA_NUM_CHANNELS =16 CORE_NUM_TOTAL_PINS =34 CORE_NUM_DIGITAL =34 CORE_NUM_INTERRUPT =34...

correction: digitalWriteFast() is SINGLE CYCLE that is 96 Mhz (teensy @ 96 Mhz) toggling which requires 2 digitalWriteFast() is ~ 48 Mhz. So in Frank B's, 3 Mhz result, the performance is from 96 Mhz to 3 Mhz (just by adding negation & digitalReadFast())

Dear all, thanks for replying! @Theremingenieur Yeap, i did not know loop() had such an overhead ... Using registers is always faster, sure, but I recall Paul saying digitalWriteFast() could be as Fast as ~50 Mhz...

I am very interested in maximum GPIO speed for teensy 3 series. I am aware from previous posts, that digitalWriteFast() can be extremely fast on teensy 3 I came across an interesting comparison of GPIO speeds of various MCUs, in this site...