Fast I/O in Arduino IDE and external class

[KamilTomaszewski]

@mezmerizer

In the Arduino IDE go to Tools -> Board: "Spresense" -> Boards Manager... Look for "Spresense" and click the update button.

Best Regards,
Kamil Tomaszewski

[MezmerizeR]

Hey @kamiltomaszewski,

I'll give it a try on monday!

Best,
MezmerizeR

[MezmerizeR]

Hey @KamilTomaszewski,

this is the code I'm using right now. Actually just the code from the docs.

volatile uint8_t *port = portOutputRegister(digitalPinToPort(3));
void setup() {
pinMode(3, OUTPUT);
}

void loop() {
*port = 1; /* High */
*port = 0; /* Low  */
}

It has no compile or linker errors but it has also no effect. So my pin 3 on the extension board is doing nothing. If I use digitalWrite it still works as expected.

Best,
MezmerizeR

[KamilTomaszewski]

Hi @MezmerizeR I found what causes this issue. It will be fixed. Currently, please try the code below:

volatile uint32_t *port = (volatile uint32_t *)portOutputRegister(digitalPinToPort(3));
void setup() {
pinMode(3, OUTPUT);
}

void loop() {
*port = 1; /* High */
*port = 0; /* Low  */
}

Please use uint32_t * instead of uint8_t * for this function.

Best Regards,
Kamil Tomaszewski

[MezmerizeR]

Hey @KamilTomaszewski,

works like a charm. Thank you!

Best,
MezmerizeR

[MezmerizeR]

Hey again,

the following code makes a difference in HIGH and LOW times of the pulse.

#include <MP.h>

#ifdef SUBCORE
  #if (SUBCORE == 1)
    uint8_t pinNo = 3;
    volatile uint32_t *port = (volatile uint32_t *)portOutputRegister(digitalPinToPort(pinNo));
    #define CORENO 1
  #endif
  #if (SUBCORE == 2)
    uint8_t pinNo = 4;
    volatile uint32_t *port = (volatile uint32_t *)portOutputRegister(digitalPinToPort(pinNo));
    #define CORENO 2
  #endif
  #if (SUBCORE == 3)
    uint8_t pinNo = 5;
    volatile uint32_t *port = (volatile uint32_t *)portOutputRegister(digitalPinToPort(pinNo));
    #define CORENO 3
  #endif
  #if (SUBCORE == 4)
    uint8_t pinNo = 6;
    volatile uint32_t *port = (volatile uint32_t *)portOutputRegister(digitalPinToPort(pinNo));
    #define CORENO 4
  #endif

void setup() {
  pinMode(pinNo, OUTPUT);
  MP.begin();
}

void loop() {
  while(1){
    *port = 1; /* High */
    *port = 0; /* Low  */
  }
}

#else

void setup() {
  MP.begin(1);  // use only this -> ~760 ns
//  MP.begin(2); // additional 760 ns -> ~1520 ns
//  MP.begin(3); // ...
//  MP.begin(4); // ... more than 3 µs
}

void loop() {
}
#endif

The problem is when using multi-core programming. WITHOUT using the code on multiple cores, the pulses are about 760 ns. WITH multiple cores the pulses are X*760 ns, where X is the number of cores that I'm using. Is there a way (except maybe assembler code) to get it faster when I use multi-core programming? Or is this a limitation due to sequential commands of the CPU or something like this?

Thanks,
MezmerizeR

[KamilTomaszewski]

@mezmerizer Don't you measure the time the MP.begin() function takes to execute? I mean you mainly consider the time the main core needs to initialize the sub cores.

Best Regards,
Kamil Tomaszewski

[MezmerizeR]

Hey @kamiltomaszewski,

I'm measuring the signals on the pins (3,4,5,6 in that case), that are produced by the different subcores with an oscilloscope.

Best,
MezmerizeR

[KamilTomaszewski]

@mezmerizer I checked it and it is unfortunately a limitation due to the bus architecture. The bus I/O access is serialized and cannot be multiplexed.

Best Regards,
Kamil Tomaszewski

[MezmerizeR]

Hey @KamilTomaszewski ,

ok, good to know. Thank you for your support!

Best regards,
MezmerizeR