Hi
U8GLIB_NHD27OLED_GR u8g(3, 4, 5, 6); // SPI Com: SCK = 3, MOSI = 4, CS = 5, A0 = 6
HW and SW SPI is selected based on the number or arguments. With the constructor above, you will always select SW SPI.
HW SPI is only available at specific Pins of the Due (109 MOSI and 110 clock, if i remember correctly). So you just need to remove the first two arguments and reconnect SCK and MOSI:
U8GLIB_NHD27OLED_GR u8g(5, 6); // HW SPI, CS = 10, A0 = 9
The other slow down is caused by the fact that the analog read is part of your picture loop:
A little bit simplified, your code looks like this:
void loop(void) {
u8g.firstPage();
do {
sensorValue = analogRead(A0);
u8g.setPrintPos(80, 62);
u8g.print(sensorValue);
} while( u8g.nextPage() );
}
Instead do this:
void loop(void) {
sensorValue = analogRead(A0);
u8g.firstPage();
do {
u8g.setPrintPos(80, 62);
u8g.print(sensorValue);
} while( u8g.nextPage() );
}
Details on the picture loop are given here: Google Code Archive - Long-term storage for Google Code Project Hosting.
Additional speedup is possible (but also more RAM will be used) with the 2X constructor.
Hope this helps to solve your performance problems.
Oliver