CADT SPO4025c
	Pseudo code for receiving generic protocol
	------------------------------------------

#define MarkChar (char)0xFF
#define QuoteChar (char)0xFE
#define AckChar	(char)0xFD
#define NakChar	(char)0xFC
#define EventChar (char)0xFB


class COximeter {
	// USB device handle
	FT_HANDLE ftHandle;
	// RS232 serial port device handle
	HANDLE hSerial;

	char cPacket[128]; // packet buffer
	int iPacketType,iPacketSize;
	..

public:
	..
	int OnRxPacket();
	..

	friend unsigned long _stdcall PacketProtocol(void *pParameters);
	}

static unsigned long _stdcall PacketProtocol(void *pParameters) {
	COximeter *pOx;
	bool bQuote;
	short iSequence,iPhase;
	short sChecksum;
	char cRxBuffer[256];
	char cChecksum;

	DWORD dwLenReceived;

	iPhase=99;
	while (true) {
		.. fetch USB or COM input data

		// read chunk of received bytes from buffer
		for (unsigned int ic=0; ic<dwLenReceived; ic++) {
			char c1=cRxBuffer[ic];
			if (c1==MarkChar) {
				if (iPhase!=99) {
					// phase error


					}
				iRxWrite=0;
				iPhase=0;
				bQuote=false;
				}
			else if (c1==QuoteChar) {
				bQuote=true;
				}
			else if (c1==AckChar) {
				iPhase=6;
				}
			else if (c1==NakChar) {
				iPhase=8;
				}
			else if (c1==EventChar) {
				// drop event character
				iPhase=99;
				}
			else if (iPhase==0) {
				// get sequence number
				iSequence=c1 & 0x07F;
				sChecksum=iSequence;
				iPhase++;
				}
			else if (iPhase==1) {
				// get packet type number
				pOx->iPacketType=c1 & 0x07F;
				sChecksum+=pOx->iPacketType;
				iPhase++;
				}
			else if (iPhase==2) {
				// get packet size number
				pOx->iPacketSize=c1 & 0x0FF;
				sChecksum+=pOx->iPacketSize;
				iPhase++;
				}
			else if (iPhase==3) {
				// get packet data
				if (bQuote) {
					c1|=(char)0x80;
					bQuote=false;
					}
				pOx->cPacket[iRxWrite++]=c1;
				sChecksum+=c1 & 0x0FF;
				if (iRxWrite==pOx->iPacketSize)
					iPhase++;
				}
			else if (iPhase==4) {
				// get checksum and check
				cChecksum=0x7F & (sChecksum ^ (sChecksum >> 7) ^ (sChecksum >> 14));
				char cAck[3];
				if (cChecksum==c1) {
					// send the ack sequence
					cAck[0]=AckChar;
					pOx->iNRxAck++;
					}
				else {
					// send the nak sequence
					cAck[0]=NakChar;
					pOx->iNRxNak++;
#ifdef _DEBUG
					sprintf(cDebug,"Oximeter NAK sent.\n");
					OutputDebugString(cDebug);
#endif // _DEBUG
					}
				cAck[1]=iSequence;
				cAck[2]=EventChar;
				if (pOx->hSerial) {
					iStatus=WriteFile(pOx->hSerial,cAck,3,&dwLenWritten,NULL);
					if (!iStatus) {
						iStatus=GetLastError();
						goto x99;
						}
					}
				else {
					iStatus=FT_Write(pOx->ftHandle,cAck,3,&dwLenWritten);
					if (iStatus!=FT_OK)
						goto x99;
					}
				if (cChecksum==c1) {
#ifdef _DEBUG
//						if (!iSequence) {
						char *pcWrite=cDebug+sprintf(cDebug,"PacketProtocol(): %02X %02X type=%02X size=%02X -",
								 0x00FF,iSequence & 0x00FF,pOx->iPacketType & 0x00FF,
								 pOx->iPacketSize & 0x00FF);
						// data bytes
						for (int i1=0; i1<pOx->iPacketSize; i1++) 
							pcWrite+=sprintf(pcWrite," %02X",pOx->cPacket[i1] & 0x00FF);
						// checksum
						pcWrite+=sprintf(pcWrite," - %02X\n",cChecksum);
//							OutputDebugString(cDebug);
//							}
#endif // _DEBUG
					pOx->OnRxPacket();
					}
				iPhase++;
				}
			// phase 5 is dropping after complete packet
			else if (iPhase==6) {
				// waiting for Ack sequence character
				if (c1!=pOx->cTxSequ)
					// treat bad packet sequence number like Nak
					goto x98;
				pOx->iNTxAck++;
				// disable transmitter
				pOx->lTxTicks=0xFFFFFFFFL;
				pOx->OnTxPacket();
				iPhase++;
				}
			// phase 7 is dropping after Ack packet
			else if (iPhase==8) {
				// waiting for Nak sequence character

				pOx->iNTxNak++;
x98:
				if (5<pOx->iNTxRepeat) {
					// immediate repeat packet transmission 
					pOx->lTxTicks=GetTickCount();
					if (pOx->hEvents[1]!=INVALID_HANDLE_VALUE)
						SetEvent(pOx->hEvents[1]);
					}
				else {
					// give up on this packet
					pOx->iNTxFailed++;
					pOx->lTxTicks=0xFFFFFFFFL;
					pOx->OnTxFailed();
					}
				iPhase++;
				}
			// phase 9 is dropping after Nak packet
			} // received character loop
		} // characters available in queue and received


The packet receiver routine looks like this

#define IBOK 0x00 
#define IBSensorDisconnected 0x01 
#define IBNoFingerInProbe 0x02
#define IBLowPerfusion 0x03
#define IBSelftestError 0x45

int COximeter::OnRxPacket() {

	// sSample is lower half of 32 bit sample number
	// 300 samples per second (runs in steps of 6)
	// use sSample or the packet iSequence number to detect missing
	// packets
	unsigned short sSample=(cPacket[0] & 0x0FF)+(cPacket[1]<<8);

	unsigned short sIR=(cPacket[2] & 0x0FF)+(cPacket[3]<<8);
	short sIR2=(cPacket[4] & 0x0FF)+(cPacket[5]<<8);
	short sCurIR=(cPacket[6] & 0x0FF)+(cPacket[7]<<8);
	short sLEDIR=255-(unsigned char)cPacket[28];
	unsigned short sRed=(cPacket[8] & 0x0FF)+(cPacket[9]<<8) /* + short(double(sIR)/7.9 ) */;
	short sRed2=(cPacket[10] & 0x0FF)+(cPacket[11]<<8) /* + short(double(sIR)/7.9 ) */;
	short sCurRed=(cPacket[12] & 0x0FF)+(cPacket[13]<<8);
	short sLEDRed=255-(unsigned char)cPacket[29];
	unsigned short sOra=(cPacket[14] & 0x0FF)+(cPacket[15]<<8);
	short sOra2=(cPacket[16] & 0x0FF)+(cPacket[17]<<8);
	short sCurOra=(cPacket[18] & 0x0FF)+(cPacket[19]<<8);
	short sLEDOra=255-(unsigned char)cPacket[30];
	unsigned short sGain=cPacket[31] & 0x00FF;
	HCRTOS=(unsigned char)cPacket[32];
	short HCFlags=cPacket[33] & 0x0FF;

	// pChildView is an object showing the plethysmogram curves
	VisPleth(pChildView,(double(8*4095-sIR)*double(255-sGain))/double(sLEDIR));
	VisPleth(pChildView,(double(8*4095-sRed)*double(255-sGain))/double(sLEDRed));

	short sSensorR=(cPacket[20] & 0x0FF)+(cPacket[21]<<8);
	short sAmbient=(cPacket[22] & 0x0FF)+(cPacket[23]<<8);
	short sGenerator=(cPacket[24] & 0x0FF)+(cPacket[25]<<8);
	short sTemperature=(cPacket[26] & 0x0FF)+(cPacket[27]<<8);

	if (iPacketType==36) {
		// extended packet with oximetry results

		short HCInfoByte=cPacket[34] & 0x0FF;

		char *pc1=NULL;
		if (HCInfoByte==IBOK)
			pc1="OK";
		else if (HCInfoByte==IBSensorDisconnected)
			pc1="Sensor?";
		else if (HCInfoByte==IBNoFingerInProbe)
			pc1="Finger?";
		else if (HCInfoByte==IBLowPerfusion)
			pc1="Perfusion?";
		else if (HCInfoByte==IBSelftestError)
			pc1="Selftest?";


		short HCPCount=(cPacket[36] & 0x0FF)+(cPacket[37]<<8);
		short HCPerf=(cPacket[38] & 0x0FF)+(cPacket[39]<<8);
		short HCPuls=(cPacket[40] & 0x0FF)+(cPacket[41]<<8);
		short HCRise=(cPacket[42] & 0x0FF)+(cPacket[43]<<8);
		short HCJitter=(cPacket[44] & 0x0FF)+(cPacket[45]<<8);
		short HCSPO2=(cPacket[46] & 0x0FF)+(cPacket[47]<<8);
		short HCHBCO=(cPacket[48] & 0x0FF)+(cPacket[49]<<8);

		}

	}