LTCDecode.cpp

00001 #include "LTCApp.h"
00002 
00003 
00004 const uint32_t minBitPeriodUS =
00005     (uint32_t)((1000000.0f / 2400) / 1.1f); // allow for 10% time error
00006 const uint32_t maxMidSymbolTimeUS = (uint32_t)(
00007                                         ((1000000.0f / (1920 * 2))) * 1.1f); // allow for 10% time error
00008 
00009 
00010 LTCDecode::LTCDecode(const PinName pin) : _LTCIn(pin)
00011 {
00012     LTCsynced = false;
00013     inputTimer.reset();
00014     inputTimer.start();
00015     FrameCallback = NULL;
00016 }
00017 
00018 void LTCDecode::enable(bool enable)
00019 {
00020     LTCsynced = false;
00021     if (enable) {
00022         inputTimer.start();
00023         inputTimer.reset();
00024         _LTCIn.fall(callback(this, &LTCDecode::LTCOnEdge));
00025         _LTCIn.rise(callback(this, &LTCDecode::LTCOnEdge));
00026     } else {
00027         inputTimer.stop();
00028         _LTCIn.fall(NULL);
00029         _LTCIn.rise(NULL);
00030     }
00031 }
00032 
00033 void LTCDecode::LTCOnEdge()
00034 {
00035     uint32_t transitionTime = inputTimer.read_us();
00036     uint32_t period = (transitionTime - lastTransition);
00037     lastTransition = transitionTime;
00038     bool gotSync = false;
00039 
00040     if (period > maxMidSymbolTimeUS) { // time since last transition is > maximum time for
00041         // a 1, must be a zero and start of the next bit. 
00042         lastBitStart = transitionTime;
00043         addBitToBuffer(false); 
00044         return;// can't be an end of frame, they must end on a 1
00045     }
00046 
00047     // if it's not a 0 it must be a 1 but are we at the end of the bit yet?
00048     if ((transitionTime - lastBitStart)> minBitPeriodUS) { // end of a bit
00049         lastBitStart = transitionTime;
00050         gotSync = addBitToBuffer(true);
00051         if (gotSync) {
00052             LTCsynced = true;
00053             decodeTime();
00054             if (FrameCallback)
00055                 FrameCallback.call();
00056         }
00057     }
00058 }
00059 
00060 // add a bit. Return true if we got the end of frame pattern
00061 bool LTCDecode::addBitToBuffer(bool bit)
00062 {
00063     LTCBuffer[0] = LTCBuffer[0]>>1;
00064     if (LTCBuffer[1] & 0x01)
00065         LTCBuffer[0] |= 0x80000000;
00066 
00067     LTCBuffer[1] = LTCBuffer[1]>>1;
00068     if (LTCBuffer[2] & 0x01)
00069         LTCBuffer[1] |=  0x80000000;
00070 
00071     LTCBuffer[2] = LTCBuffer[2]>>1;
00072     if (bit)
00073         LTCBuffer[2] |=  0x80000000;
00074 
00075    // frame sync patterin is 1011 1111 1111 1100
00076     // if it's a valid sync we will have it just received (buffer2 top bits) and the one from the last frame still in the buffer as the low 16 bits of buffer 0.
00077     return ((((LTCBuffer[2]>>16) & 0x0000FFFF) == 0xBFFC) && ((LTCBuffer[0] & 0x0000FFFF) == 0xBFFC));
00078 }
00079 
00080 void LTCDecode::decodeTime()
00081 {
00082     _frame =        ((LTCBuffer[0]>>16) & 0x0f) + ((LTCBuffer[0] >> 24) & 0x03) * 10;
00083     _seconds =      ((LTCBuffer[1]>>0) & 0x0f) + ((LTCBuffer[1] >> 8) & 0x07) * 10;
00084     _minutes =      ((LTCBuffer[1]>>16) & 0x0f) + ((LTCBuffer[1] >> 24) & 0x07) * 10;
00085     _hours =      ((LTCBuffer[2]>>0) & 0x0f) + ((LTCBuffer[2] >> 8) & 0x03) * 10;
00086     _frameDrop = (LTCBuffer[0] & (1<<26));
00087 }