The challenge:
To take consecutive readings from bytes 2 and 3 of frame 0x480 of can bus and calculate average fuel consumption. Bytes 2 & 3 give a continuous incremental reading of fuel consumed in microlitres. (Note: the first bit of data is just a marker bit so the data is only 15 bits long).

Requirements:
To get accurate timestamp of data
To keep a rolling average to smooth out data
To deal with rollover of time and fuel data. e.g. as fuel consumption data is 15 bit it reaches hex 7FFFFFF (dec 32767 ) before rolling back to zero

Managed so far:
To obtain continuous output from 0x480 with flexcan timestamp

Sample data:
Timestamp-- bin-- dec
31910-- 111111111101111-- 32751
41943-- 111111111110100-- 32756
51976-- 111111111111001-- 32761
62008-- 111111111111110-- 32766
6506-- 11-- 3
16537-- 1000-- 8
26569-- 1101-- 13
36602-- 10010-- 18
46636-- 10111-- 23
56668-- 11100-- 28

Code theory:
Code:
	fuel = ((( inMsg.buf[3]&0b01111111)<<8)+inMsg.buf[2]); 

	if fuel2>fuel1 
	fuelused = fuel2-fuel1 
	else fuelused=((fuel2+32767)-fuel1)

     
	if time2>time1 
	timediff = time2-time1 
	else timediff=((time2+65535)-time1)

	fuelrate = (360/timediff)*fuelused
Question:
How do I get sequential readings from 0x480 so that I can obtain fuel1, fuel2, time1 & time 2 to then perform my calculation?

How do I keep a rolling average of the readings to smooth the data?

Main code for reference:
Code:
void PollEngineCAN(){ //function to poll engine data
  CAN_message_t inMsg;
  
  if (Can1.available()>0){
      Can1.read(inMsg); //read message into inMsg
      switch ( inMsg.id ) { //a type of if process that can check for multiple conditions
        case 0x280:
          torque = ( inMsg.buf[1]*0.39 );
          rpm = ((( inMsg.buf[3]<<8)+inMsg.buf[2])/4); 
          LastRPM=millis(); //timestamp the last rpm reading
          break;
        case 0x288:
          coolant = (( inMsg.buf[1]*0.75)+225.15); //convert from C to K (-48 + 273.15 = 225.15)
          break;
//        case 0x480:
//        if/else required here 
//        e.g. if fuel2>fuel1 then fuelused = fuel2-fuel1 else fuelused=((fuel2+32767)-fuel1)
//        fuel = ((( inMsg.buf[3]&0b01111111)<<8)+inMsg.buf[2]); //factor into l/h
//        break;
        case 0x588:
          boost = ( inMsg.buf[4]*1000 ); //convert from bar to Pa (*0.01 x 100,000 = 1000)
          break;
      }  
    }
  }