spi0Slave6.ino Slave part of 2Nanos. Just starting..

 // Written by Nick Gammon.
// February 2011. PB: going to test three-pin PCINT0_vect
//SS pin interrupt OK and receiving two adr Hi and Lo from Master with 2uS delay
/* Fri Jul  3 11:02:43 NZST 2020

*/
#include <SPI.h>
#define clockTo1802Pin 3
volatile boolean gotSS=false,SSFell=false;
uint16_t  PB2Ints=0,SSFallen=0;
uint16_t DELAY = 300;
byte adr0,adr1,tempByte0;
byte oldPortBVal=0x07;
byte newPortBVal,oldNewXOR;
byte SSMask=0b00000100;		//SS* = PB2
boolean newAdrComing = false,weirdPCINT0 = false;
//boolean doGotAdr = false;
boolean doingPCISR =false;
//boolean showAdr = false;
boolean gotAdr = false;
volatile byte c;
void setup (void) {
  pinMode(clockTo1802Pin,OUTPUT);  //D3 goes to 1802 clock
  pinMode(10,INPUT);    //this is SS* pin
  pinChangeSetup();
  Serial.begin (115200);   // debugging
 // justStepping();
// justClocking();
  // turn on SPI in slave mode
  SPCR =(1<<SPE);

  // have to send on master in, *slave out*
  pinMode(MISO, OUTPUT);

  SPI.attachInterrupt();

}  // end of setup


// SPI interrupt routine
ISR (SPI_STC_vect) {
  c = SPDR;  // grab byte from SPI Data Register
  if (SSFell==true){
	adr0=c;
	SSFell=false;
  } else {
	adr1=c;
	gotAdr=true;
  }	//need 2uS gap between adresses to make this work.
}  // end of interrupt routine SPI_STC_vect

//-----------------------------
void loop (void) {
	digitalWrite(clockTo1802Pin,HIGH);
	if ( gotAdr)   {
		doGotAdr();
    }
	delay(DELAY);
	digitalWrite(clockTo1802Pin,LOW);
	if (doingPCISR==true) { doingPCISR = false; Serial.print("$$");}
	delay(DELAY);
}  //---------------------

void pinChangeSetup(void) { //make SS*pin = pin10 subject to pin change interrupt.
    PCICR=0x01;     //turn on PORTB pin change interripts
    PCMSK0=0x04;    //just do pin change interrupt on PCINT2 aka Pb2 aka pin10 aka SS*
}
ISR(PCINT0_vect) {
	weirdPCINT0 = false;
	newPortBVal=PINB;
	oldNewXOR=oldPortBVal^newPortBVal; 	//which bit was changed.
	doingPCISR = true;
	switch(oldNewXOR & 0x04){
		case 0x04:	//SS*
			PB2Ints++;
			if((newPortBVal & SSMask)==0 ) {	//if pinchange 1-->0
					SSFallen++;
					SSFell=true;
					newAdrComing = true;
			}
			break;

		default:
			weirdPCINT0 = true;
			Serial.println(F("weird PCINT0"));
			tempByte0 = oldNewXOR & 0x04;
		break;
	}
  oldPortBVal=newPortBVal;
}
void justStepping(void) {
  while(true) {
    Serial.print("step");
    delay(1000);
  }
}
  void justClocking(void) {
  while(true) {
    //Serial.print("step");
    digitalWrite(3,HIGH);
    delay(32);
    digitalWrite(3,LOW);
    delay(32);
  }
}
void doGotAdr(void) {
	Serial.print("##");
if (SSFell==true) {Serial.print("SS Fell=true"); }
    Serial.println(PB2Ints);
    Serial.println(SSFallen);
    Serial.print("++");Serial.print(adr0,HEX);Serial.println(adr1,HEX);
	if (weirdPCINT0==true) {Serial.print("--");Serial.print(tempByte0,HEX);}
	gotAdr=false;
}