This is my first time posting on this forum. So, recently I purchased the Arduino Due after months of tinkering with the Uno. When using the Uno, port manipulation was a bit easier using DDR and PORTx. When I made the jump from an AVR board to an ARM, I was stuck on how to do port manipulation for the Due. I first started with a simple blinking LED program to understand how to set and clear bits. The simple code is shown below.
void setup() {
REG_PIOB_PER = (1<<25); //Can also use bit mask - 0x1<<25
REG_PIOB_OER = (1<<25); //Can also use REG_PIOB_OER = PIO_OER_P25
}
void loop() {
REG_PIOB_SODR = (1<<25);
delay(2000);
REG_PIOB_CODR = (1<<25);
delay(2000);
}
Now I want to write a program that will use PWM on the LED. After a little research, I found that each I/O pin can have be multiplexed to have two functions. What is multiplexing and how can it be done in a simple example? Also, how can I write a program to set up PWM using low-level programming?
I found that each I/O pin can have be multiplexed to have two functions[/quote]
You have the explanation of this chap 9.3 of Sam3x datasheet.
For PWM programming, here is an example :
void setup () {
// PWM Set-up on pin PC7 (Arduino Pin 39): see Datasheet chap. 38.5.1
// Select Instance=PWM; Signal=PWMH2 (channel 2); I/O Line=PC7 (P7, Arduino pine 39, see pinout diagram) ; Peripheral=B
PMC->PMC_PCER1 |= PMC_PCER1_PID36; // PWM on
REG_PIOC_ABSR |= PIO_ABSR_P7; // Set PWM pin perhipheral type B
REG_PIOC_PDR |= PIO_PDR_P7; // Set PWM pin to an output
REG_PWM_ENA = PWM_ENA_CHID2; // Enable the PWM channel 2 (see datasheet page 973)
REG_PWM_CLK = PWM_CLK_PREA(0) | PWM_CLK_DIVA(42); // Set the PWM clock rate to 2MHz (84MHz/42). Adjust DIVA for the resolution you are looking for
REG_PWM_CMR2 = PWM_CMR_CALG |PWM_CMR_CPRE_CLKA; // The period is left aligned, clock source as CLKA on channel 2
REG_PWM_CPRD2 = 1000000; // Channel 2 : Set the PWM frequency 2MHz/(2 * CPRD) = F ; 1< CPRD < 2exp24 -1 ; here CPRD = 10 exp 6
REG_PWM_CDTY2 = 200000; // Channel 2: Set the PWM duty cycle to x%= (CDTY/ CPRD) * 100 % , CDTY = 2 * 10 exp 5
// Alternatively, you can use this format : PWM->PWM_CH_NUM[2].PWM_CPRD = 1000000 ;
// In this example, Frequency is 1 HZ with a DT of 20% so you can see it with an LED attached to pin 39 with a resistor
}
void loop() {
}
So, from my understanding, all the pins on the due are controlled by the PIO controllers that are capable of controlling 32 lines(pins). Each pin ( or line) can do two functions which are chosen from the start and once a peripheral function is chosen, you can not reset to the other function. Is that pretty much how it is? Thank you for the reply, the example worked well!