LTC Timecode Reader using Arduino - arduino

Question

I posted a little while ago on here and you were really helpful. And i've managed to adapt some code to get it working on an lcd display.
What I would like some extra help with is firstly is there a way of defining the one_time_max etc different depending on the high low state of a pin. This way i could use a switch to change the times so it could switch between NTSC and PAL.
Secondly would anyone be kind enough to explain what is happening in the middle part of this code. I understand that there is a volatile boolean which can be true of false. But later in the code you make an IF statement against it and I don't fully understand how that works. Any help would be appreciated.
Here is a picture of how it's going so far. I'll keep you guys up to date as the project continues :)
// Code from forum post Dec 12, 2007
//
//
// include the library code:
#include <LiquidCrystal.h>
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
#define one_time_max 600 // these values are setup for PA video
#define one_time_min 400 // It's the durstion of a one and zero with a little bit of room for error.
#define zero_time_max 1050 //
#define zero_time_min 950 //
#define icpPin 8 // ICP input pin on arduino
//#define one_time_max 475 // these values are setup for NTSC video
//#define one_time_min 300 // PAL would be around 1000 for 0 and 500 for 1
//#define zero_time_max 875 // 80bits times 29.97 frames per sec
//#define zero_time_min 700 // equals 833 (divide by 8 clock pulses)
#define end_data_position 63
#define end_sync_position 77
#define end_smpte_position 80
volatile unsigned int pin = 13;
volatile unsigned int bit_time; // volatile instructs the variable to be stored in RAM
volatile boolean valid_tc_word; // booleon can be either of two values true or false
volatile boolean ones_bit_count; // booleon can be either of two values true or false
volatile boolean tc_sync; // booleon can be either of two values true or false
volatile boolean write_tc_out; // booleon can be either of two values true or false
volatile boolean drop_frame_flag; // booleon can be either of two values true or false
volatile byte total_bits; //this stores a an 8-bit unsigned number
volatile byte current_bit; //this stores a an 8-bit unsigned number
volatile byte sync_count; //this stores a an 8-bit unsigned number
volatile byte tc[8]; //this stores a an 8-bit unsigned number
volatile char timeCode[11]; //this stores a an 8-bit unsigned number
/* ICR interrupt vector */
ISR(TIMER1_CAPT_vect) //ISR=Interrupt Service Routine, and timer1 capture event
{
//toggleCaptureEdge
TCCR1B ^= _BV(ICES1); //toggles the edge that triggers the handler so that the duration of both high and low pulses is measured.
bit_time = ICR1; //this is the value the timer generates
//resetTimer1
TCNT1 = 0;
if ((bit_time < one_time_min) || (bit_time > zero_time_max)) // this gets rid of anything that's not what we're looking for
{
total_bits = 0;
}
else
{
if (ones_bit_count == true) // only count the second ones pluse
ones_bit_count = false;
else
{
if (bit_time > zero_time_min)
{
current_bit = 0;
sync_count = 0;
}
else //if (bit_time < one_time_max)
{
ones_bit_count = true;
current_bit = 1;
sync_count++;
if (sync_count == 12) // part of the last two bytes of a timecode word
{
sync_count = 0;
tc_sync = true;
total_bits = end_sync_position;
}
}
if (total_bits <= end_data_position) // timecode runs least to most so we need
{ // to shift things around
tc[0] = tc[0] >> 1;
for(int n=1;n<8;n++) //creates tc[1-8]
{
if(tc[n] & 1)
tc[n-1] |= 0x80;
tc[n] = tc[n] >> 1;
}
if(current_bit == 1)
tc[7] |= 0x80;
}
total_bits++;
}
if (total_bits == end_smpte_position) // we have the 80th bit
{
total_bits = 0;
if (tc_sync)
{
tc_sync = false;
valid_tc_word = true;
}
}
if (valid_tc_word)
{
valid_tc_word = false;
timeCode[10] = (tc[0]&0x0F)+0x30; // frames this converst from binary to decimal giving us the last digit
timeCode[9] = (tc[1]&0x03)+0x30; // 10's of frames this converst from binary to decimal giving us the first digit
timeCode[8] = ':';
timeCode[7] = (tc[2]&0x0F)+0x30; // seconds
timeCode[6] = (tc[3]&0x07)+0x30; // 10's of seconds
timeCode[5] = ':';
timeCode[4] = (tc[4]&0x0F)+0x30; // minutes
timeCode[3] = (tc[5]&0x07)+0x30; // 10's of minutes
timeCode[2] = ':';
timeCode[1] = (tc[6]&0x0F)+0x30; // hours
timeCode[0] = (tc[7]&0x03)+0x30; // 10's of hours
drop_frame_flag = bit_is_set(tc[1], 2); //detects whether theree is the drop frame bit.
write_tc_out = true;
}
}
}
void setup()
{
lcd.begin (16, 2);
pinMode(icpPin, INPUT); // ICP pin (digital pin 8 on arduino) as input
bit_time = 0;
valid_tc_word = false;
ones_bit_count = false;
tc_sync = false;
write_tc_out = false;
drop_frame_flag = false;
total_bits = 0;
current_bit = 0;
sync_count = 0;
lcd.print("Finished setup");
delay (1000);
TCCR1A = B00000000; // clear all
TCCR1B = B11000010; // ICNC1 noise reduction + ICES1 start on rising edge + CS11 divide by 8
TCCR1C = B00000000; // clear all
TIMSK1 = B00100000; // ICIE1 enable the icp
TCNT1 = 0; // clear timer1
}
void loop()
{
if (write_tc_out)
{
write_tc_out = false;
if (drop_frame_flag)
lcd.print("TC-[df] ");
else
lcd.print("TC-NO DROP FRAME");
lcd.setCursor(0, 1);
lcd.print((char*)timeCode);
lcd.print("\r");
lcd.setCursor(11, 1);
lcd.print("......");
delay (40);
lcd.clear(); } }

Answer 1

an if removed from the type declaration should not affect the «volatile» keyword as shown in the code ▬ compiler-writers have a trade-off where folks want to do systems ( stuff like here ) and it jams the machine so they tell you volatileis some sort of exotic thing but is far from that when used here
it is the way it should be here ~ that is not a business machine