ESP8266 for HDLC decoding, AX.25, APRS (2024)

/**************************************************************Function name: aprs_wait_begin() Parameters: None Return value: bool true = get legal pulse, false = not get Explanation: Wait for the first 833us high pulse, the judgment range is 730-930, others are ignored***************************************************************/bool aprs_wait_begin(){static unsigned long lastTime = micros();static unsigned char lastLevel = digitalRead(APRS_DATA_IO);unsigned char nowLevle = digitalRead(APRS_DATA_IO);//Rising edge, set the pulse start timeif(nowLevle && !lastLevel){lastLevel = nowLevle;lastTime = micros();}//Falling edge, judge the pulse widthelse if(!nowLevle && lastLevel){long pulseTime = micros()-lastTime;lastLevel=nowLevle;//Legal pulse is judged at 833us plus or minus 100us, it can be smallerif(pulseTime>730 && pulseTime<930){return true;}}return false;} //end aprs_wait_begin()/************************************************************** Function name: aprs_rx_data() Parameters: None Return value: None Explanation: This function is in blocking mode and will not exit before the reception is completed or timeout 1200bps, 1200 bits per second, 833us per bit width Level flip = logic 0, level remains unchanged = logic 1 After getting the first legal pulse, start to receive data in bytes, and save it once every 8 bits At this time, you will also receive Flag:0x7E, that is: 6 consecutive "1"s Check the value of sameBit when the level is flipped 6 consecutive "1" bytes are the first byte of data And mark isData=1; Received again 6 consecutive "1"s have been received In any case, receiving 7 consecutive "1" judgment data is invalid Set the sameBit to 0 after each level flip, the last time increases the current time +450us, Ensure that every 833us backward sampling point is stuck in the middle of each bit***************************************************************/void aprs_rx_data(){unsigned char bitBuf=0x00; //bit buffer receives the low bit firstunsigned char bitCount=0; //bit counter, once every 8 bits are written to the bufferunsigned char sameBit=0; //Continuous 1 counterunsigned char isData=0; //Whether the data segmentunsigned char lastLevel = digitalRead(APRS_DATA_IO);unsigned char nowLevle;unsigned long lastTime;unsigned long nowTime;//The previous program caught the first legal pulse, so it received a level flip that is "0", and the bit counter is now 1bitCount = 1; lastTime = micros() + 450;while(1){ESP.wdtFeed(); //Feed the dog, I don’t know why ESP8266 triggers the watchdog in the while.//delayMicroseconds(10);nowLevle = digitalRead(APRS_DATA_IO);nowTime = micros();//Level flipif(nowLevle != lastLevel){lastLevel = nowLevle;lastTime = nowTime+450;//According to the HDLC protocol, we regard Flag 0x7E as 6 consecutive "1"s, and insert 5 consecutive "1"s into the data to avoid 6 "1"s.//Here when less than 5, set to 0if(sameBit<5){sameBit=0;}//6 consecutive "1"s appeared, which means the end when receiving dataif(sameBit==6 && isData){toCodeFlag=1;return;}//5 consecutive "1"s, delete 0, ignore this bit and continue will bring the program back to the starting point of whileif(sameBit==5){sameBit=0; continue;}//The number of bits reaches 8, and the full 1 byte is processed accordinglyif(++bitCount==8){//Received bytes that are not 6 consecutive "1"s in the non-data segment, indicating the beginning of the dataif(!isData && sameBit != 6){isData=1;}if(!isData){continue;}//isData = 0;if(aprsCount == APRS_DATA_BUF_MAX){aprsCount=0;}aprsData[aprsCount++]=bitBuf;bitCount=0;bitBuf=0x00;}continue;}//When the level is maintained at 833us, logic 1 is obtainedif(nowTime>lastTime && (nowTime - lastTime) > 833){lastTime = nowTime;//During the data transmission process, any 7 consecutive "1"s that appear before the Flag are judged to be abnormal, and no decoding is performedif(++sameBit==7){toCodeFlag=0;return;}//Fill "1" to the specified positionbitBuf |= 0x01 << bitCount;//Collect 1 byteif(++bitCount==8){if(aprsCount == APRS_DATA_BUF_MAX){aprsCount=0;}aprsData[aprsCount++] = bitBuf;bitCount=0;bitBuf=0x00;}continue;}}// end while}//end aprs_rx_data()

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