ST7920_SPI_master library not using delays for glcd128x64

Other Hardware Displays
7

Another thing I started to notice.

When I clear the display with the current speed which is 1000000UL there are some pixels left over because the speed is still a bit fast than enough.

I used 500000 is problem is solved.

void glcd_cmd(uint8_t cmd) {
  SPI.beginTransaction(SPISettings(500000, MSBFIRST, SPI_MODE3));
  digitalWrite(CS_PIN, HIGH);
  SPI.transfer(0xF8);
  SPI.transfer(cmd & 0xF0);
  SPI.transfer(cmd << 4);
  digitalWrite(CS_PIN, LOW);
  SPI.endTransaction();
}

void glcd_data(uint8_t data){
  SPI.beginTransaction(SPISettings(500000, MSBFIRST, SPI_MODE3));
  digitalWrite(CS_PIN, HIGH);
  SPI.transfer(0xFA);
  SPI.transfer(data & 0xF0);
  SPI.transfer(data << 4);
  digitalWrite(CS_PIN, LOW);
  SPI.endTransaction();
}

My question, how to balance the best SPI speed for this glcd ?

If I put any speed in the setting function, would the Arduino adapt that exact speed ?

Like:

  1. This causes some left pixels on the display, so it's still too fast for the glcd
SPI.beginTransaction(SPISettings(1000000, MSBFIRST, SPI_MODE3));
  1. I used this speed and it worked fine:
SPI.beginTransaction(SPISettings(950000, MSBFIRST, SPI_MODE3));

Does it really run at 950k ?