hI GUYS,
I POSTED ON A DIFFERENT SECTION ABOUT THIS BUT DIDN'T GET MUCH LUCK. BASICALLY I'VE ADAPTED SOME CODE ON THIS SITE IN ORDER TO DISPLAY A SMPTE TIMECODE STREAM. I'VE GOT SOME QUESTIONS ABOUT THE CODE INVOLVED SO I CAN FULLY UNDERSTAND HOW IT WORKS. THE MAIN PART I DO NOT UNDERSTAND IS THE MIDDLE SECTION. WHERE YOU ARE USING VOLATILE BOOLEANS WHICH DO NOT APPEAR TO HAVE A VALUE AND THEN MAKING IF STATEMENTS BASED ON THERE NON DEFINED VALUES. IF ANYONE COULD HELP ME IN WHAT IS HAPPENING WITH THE CODE HERE THAT WOULD BE GREAT.
ALSO AS I UNDERSTAND IT THE LAST SECTION WHERE IT IS ADDING 0X0F ETC. IS THIS CONVERTING FROM HEX TO DECIMAL?
ANY HELP EXPLAINING HOW THIS CODE WORKS WOULD BE FANTASTIC AND HERE IS A PICTURE OF THE PROJECT SO FAR.
AND HERE IS THE CODE IN QUESTION.
tHANKS IN ADVANCE.
// 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 (30);
lcd.clear();
}
}