AVR Freaks

******************Code from Xplained Pro***********************************************

#define F_CPU 4000000UL

//Definicia SPI parametrov

#define SPI_PORT PORTC
#define SPI_MOSI 5
#define SPI_MISO 6
#define SPI_SCK 7
#define SPI_SS 4
#define SPI_STATUS 0x80 //SPI waiting for operation

#define SPI_TIMEOUT 800 //[uS]

#include <avr/io.h>
#include <util/delay.h>
//#include <avr/interrupt.h>

volatile int16_t i=0,j=0;  
volatile unsigned long k;

int SPI_uvod(void) //SPI init
{
    PORTC_DIRSET = (1<<SPI_MOSI);
    while(!(PORTC_DIR & (1<<SPI_MOSI)));
    
    PORTC_DIRSET = (0<<SPI_MISO);
       
    PORTC_DIRSET = (1<<SPI_SCK);
    while(!(PORTC_DIR & (1<<SPI_SCK)));
    
    PORTC_DIRSET = (1<<SPI_SS);
    while(!(PORTC_DIR & (1<<SPI_SS)));
    
    
    //SS pin high
    PORTC_OUTSET = (1<<SPI_SS);
    while(!(PORTC_IN & (1<<SPI_SS)));
    
    //SPI_master, SPI Mode=00, CLK2x=1, DORD=0, prescaler=01
    SPIC.CTRL = 0b10010001;
    SPIC.INTCTRL = SPI_INTLVL_OFF_gc ; // no interrupt
    
    //SPI enable
    SPIC.CTRL|=64;
    
    return 0;
}

int16_t SPI_citaj(void) //SPI read
{
    int16_t spi_hodnota=0;
        
    //SS pin low
    PORTC_OUTCLR = (1<<SPI_SS);
    while(PORTC_IN | (0<<SPI_SS));
    //_delay_ms(4);
    while(!(SPIC.STATUS & 0x80)) spi_hodnota=SPIC.DATA;

    //SS high
    PORTC_OUTSET = (1<<SPI_SS);
    while(!(PORTC_IN & (1<<SPI_SS)));
    //_delay_ms(4);
    return spi_hodnota;
}

uint8_t SPI_zapis(uint8_t vstup) //SPI write
{
    
    //SS pin low
    PORTC_OUTCLR=(1<<SPI_SS);
       
    SPIC.DATA=vstup;
    while(!(SPIC.STATUS & 0x80));    
    
    
    //SS high
    PORTC_OUTSET = (1<<SPI_SS);
    while(!(PORTC_IN & (1<<SPI_SS)));
    return 0;
}

void SPI_zavriet(void) //Closing SPI
{
    while(!(SPIC.STATUS & 0x80));
    SPIC_CTRL =0;
}

int main(void)
{
 
    SPI_uvod();
    
 
            
    while(1)
    {
        
    for(j=0;j<=254;j++)
    {
    
    SPI_zapis(199);
    //SPI_zapis(19);  //Command for SPI potentiometer to write value
    //SPI_zapis(j);    //Value itself
    //_delay_ms(500); //Delay, to detect changes in resistance on multimeter
    }
    }
    
    SPI_zavriet();
    
      
}

*****End of Explained Pro code

**************Reference code from Arduino Due***

#include <SPI.h>
#define SS_SPI_PIN 10 //Pin 10

void set_pot(byte pot_setting)
{
digitalWrite(SS_SPI_PIN, LOW);
SPI.transfer(byte(19)); // send command byte
SPI.transfer(byte(pot_setting)); // send value (0~255)
digitalWrite(SS_SPI_PIN, HIGH);
}

void setup (void)

  {
  pinMode(SS_SPI_PIN, OUTPUT);
  digitalWrite(SS_SPI_PIN, HIGH);  // ensure SS stays high
  SPI.begin ();
 
  Serial.begin(115200);  
  digitalWrite(SS_SPI_PIN, LOW);    // SS is LOW
 
  } // end of setup

void loop (void)
  {
  int i;
  byte c;

while(1)

{
 for(i=0;i<=255;i++)
{
  set_pot(i);
  delay(500);
}
}
 
  }

I used test value 199 to see it on osciloscope. Attached screenshots are for this value. To me they looks OK. When I was testing potentiometer I used combination of 19 and new setting value with delay. No changes on multimeter was observed.

I labeled cables to be sure and connect SPI potentiometer to Arduino Due (3.3V) using same sets of values. Everything working normal. When I connect it to Xplained Pro, wasn't working. I'm adding screenshoot from osciloscope (just cheap one, so it can be some distortion from signal...). MOSI  is pullup 20k resistor, MISO 10k pullup, SS 20k pull-down, SCK 20k pull-down. Since I have only 2 channel osciloscope, attaching combination SCK/MOSI(Blue/Yellow) and SS/MOSI (Blue/Yellow). 1 Clock is 2uS. I try different clocks, but results was the same. Hopefully someone with good HW background will be able to solve it.. Thx

Hi Jim,

I created extra function for read because read, that you should test SPIC.STATUS to be sure, that value is actual "while(!(SPIC.STATUS & 0x80)) spi_hodnota=SPIC.DATA;", but if "return SPIC.DATA" will job , even better. I tested with new function "SPI_Transfer" with 199 value, oscilloscope looks good, but when I switch to actual functionality with "SPI_Transfer(19) and SPI_Transfer(j) to change value of resistance for potentiometer, again is not working.... Not sure what is wrong...

Thx

Thank you Jim again. Now it is working.

With hint from Jim, I changed code as follow:

#define F_CPU 4000000UL

#define SPI_PORT PORTC
#define SPI_MOSI 5
#define SPI_MISO 6
#define SPI_SCK 7
#define SPI_SS 4
#define SPI_STATUS 0x80 //SPI waiting for operation

#define SPI_TIMEOUT 800 //[uS]

#define SS_PIN_HIGH      PORTC_OUTSET = (1<<SPI_SS); while(!(PORTC_IN & (1<<SPI_SS))) //SS pin HIGH
#define SS_PIN_LOW       PORTC_OUTCLR=(1<<SPI_SS); while(PORTC_IN & (1<<SPI_SS)) //SS pin LOW
#define SPI_STATUS_CHECK while(!(SPIC.STATUS & 0x80)) //Check status of SPI

#include <avr/io.h>
#include <util/delay.h>
//#include <avr/interrupt.h>

volatile int16_t i=0,j=0;
volatile unsigned long k;

int SPI_uvod(void) //SPI init
{
    PORTC_DIRSET = (1<<SPI_MOSI);
    while(!(PORTC_DIR & (1<<SPI_MOSI)));
    
    PORTC_DIRSET = (0<<SPI_MISO);
    
    PORTC_DIRSET = (1<<SPI_SCK);
    while(!(PORTC_DIR & (1<<SPI_SCK)));
    
    PORTC_DIRSET = (1<<SPI_SS);
    while(!(PORTC_DIR & (1<<SPI_SS)));
    
    
    //SS pin high

    SS_PIN_HIGH;

    
    //SPI_master, SPI Mode=00, CLK2x=1, DORD=1, prescaler=01
    SPIC.CTRL = 0b10010001;
    SPIC.INTCTRL = SPI_INTLVL_OFF_gc ; // no interrupt
    
    //SPI enable
    SPIC.CTRL|=64;
    
    return 0;
}

uint8_t SPI_Transfer(uint8_t vstup) //SPI transfer
{
    
    SPIC.DATA=vstup;
    SPI_STATUS_CHECK;
    
    return SPIC.DATA;
}

void SPI_zavriet(void) //Closing SPI

{
    SPI_STATUS_CHECK;
    SPIC_CTRL =0;
}

int main(void)
{
    
    SPI_uvod();
    
    
    
    while(1)
    {
        
        for(j=0;j<=254;j++)
        {
            
            SS_PIN_LOW;
            SPI_Transfer(19);  //Command for SPI potentiometer to write value
            SPI_Transfer(j);    //Value itself
            SS_PIN_HIGH;
            _delay_ms(500); //Delay, to detect changes in resistance on multimeter
        }
    }
    
    SPI_zavriet();
    
    
}

It was sugested to pay attention that SS is holding LOW during 2 byte transfer (as outlined in attachment).

Thx Jim again.