SPI clock acting weird

[danieleff]

I was trying Adafruit ILI9341, but was not working.
I think the following code is a simplified version of the problem:

void setup() {
  int cs = 2;
  SPI.begin();
  pinMode(cs, OUTPUT);
  digitalWrite(cs, HIGH);

  while(1) {
      SPI.beginTransaction(SPISettings(1000000, MSBFIRST, SPI_MODE0));
      delay(100);
      digitalWrite(cs, LOW);
      SPI.transfer(0x01);
      digitalWrite(cs, HIGH);
      SPI.endTransaction();
      delay(100);
  }
}

With arduino UNO, I get the following:

With F746 discovery:

or ( with F407 always)

Logic analizer settings are the same.
Can you check if you get the same results?

[fpistm]

Hi @danieleff ,

have you made those test with or without this fix?
#19

[danieleff]

With that fix:

> git show
commit 055864fb16457cd45b638f48588b85477f0eb226
Merge: dadfba3 052443e
Author: Frederic Pillon <[email protected]>
Date:   Fri Jun 9 17:36:17 2017 +0200

(Actually does not compile on 407 disco, timer.c:466:22: error: 'RCC_PeriphCLKInitTypeDef {aka struct <anonymous>}' has no member named 'TIMPresSelection', but its another issue, I commented out)

[fpistm]

I do not check yet, but seems as GPIO pull config issue.

[fpistm]

Thanks @cparata
Pull setting on the SCK pin should be in PULLDOWN if the SPI polarity is LOW and in PULLUP if the SPI polarity is HIGH.