Happiness is SdFat with DMA SPI

Official Hardware Mega Due
8

Hi.

I'm struggling to raise speed in SPI.

I've bought a Sandisk Extreme Pro for this tests now.

Even with this card, I can't go faster then clock/8.

From what I understand from your reports, this is a limitation of due and standard SDlib because it doesn't have buffers in SPI port.

Am I understanding things right?

I've currently modified the SDClass::begin function to do the init in low speed, and then raise speed.

boolean SDClass::begin(uint8_t csPin) {
  /*

    Performs the initialisation required by the sdfatlib library.

    Return true if initialization succeeds, false otherwise.

   */
   boolean state;
   state=card.init(SPI_QUARTER_SPEED, csPin);
   state&=volume.init(card);
   state&=root.openRoot(volume);
   card.setSckRate(2);
   
   return state;

Only when I send "2" in the "card.setSckRate(2)" I get the slideshow running.

With DMA, you're able to init the lib at 42MHz?