TableOfContents

Protocol

• The protocol is based on individual serial data frames that are organized as shown in the following table.

  Start-Byte	Address-Byte	ID-Byte	n Data-Bytes coded	CRC-Byte1	CRC-Byte2	Stop-Byte
  '#'	variable	'V','D' etc	"modified-base64"	variable	variable	'\r'

Commands

• The Commands based on the dataframes above are listed [:en/SerialCommands:here]

Slave Adresses

• Since Navi 0.12h FC 0.71f Mag 0.19 there are constant SlaveAdresses:

  Slave-Address	Part
  1	FC
  2	NC
  3	MK3MAG

Data Format

• Have a look into the Functions Decode64 and SendOutData in uart.c of the FC Firmware to see how the Data is encoded and decoded:

     1 void SendOutData(unsigned char cmd,unsigned char modul, unsigned char *snd, unsigned char len)
     2 {
     3  unsigned int pt = 0;
     4  unsigned char a,b,c;
     5  unsigned char ptr = 0;
     6 
     7  SendeBuffer[pt++] = '#';               // Start-Byte
     8  SendeBuffer[pt++] = modul;             // Adress 
     9  SendeBuffer[pt++] = cmd;                // Command
    10 
    11  while(len)
    12   {
    13    if(len) { a = snd[ptr++]; len--;} else a = 0;
    14    if(len) { b = snd[ptr++]; len--;} else b = 0;
    15    if(len) { c = snd[ptr++]; len--;} else c = 0;
    16    SendeBuffer[pt++] = '=' + (a >> 2);
    17    SendeBuffer[pt++] = '=' + (((a & 0x03) << 4) | ((b & 0xf0) >> 4));
    18    SendeBuffer[pt++] = '=' + (((b & 0x0f) << 2) | ((c & 0xc0) >> 6));
    19    SendeBuffer[pt++] = '=' + ( c & 0x3f);
    20   }
    21  AddCRC(pt);
    22 }
    23 
    24 void Decode64(unsigned char *ptrOut, unsigned char len, unsigned char ptrIn,unsigned char max) 
    25 {
    26  unsigned char a,b,c,d;
    27  unsigned char ptr = 0;
    28  unsigned char x,y,z;
    29  while(len)
    30   {
    31    a = RxdBuffer[ptrIn++] - '=';
    32    b = RxdBuffer[ptrIn++] - '=';
    33    c = RxdBuffer[ptrIn++] - '=';
    34    d = RxdBuffer[ptrIn++] - '=';
    35    if(ptrIn > max - 2) break;     // dont process more data than recieved
    36 
    37    x = (a << 2) | (b >> 4);
    38    y = ((b & 0x0f) << 4) | (c >> 2);
    39    z = ((c & 0x03) << 6) | d;
    40 
    41    if(len--) ptrOut[ptr++] = x; else break;
    42    if(len--) ptrOut[ptr++] = y; else break;
    43    if(len--) ptrOut[ptr++] = z; else break;
    44   }
    45 
    46 } 
  

  • ToDo: describe data-format

Checksum

•    1 unsigned int tmpCRC = 0; 
     2 for(int i = 0; i <  DataBufferLength;i++)
     3  { 
     4   tmpCRC += DataBuffer[i]; 
     5  }   
     6 tmpCRC %= 4096; 
     7 CRC1 = '=' + tmpCRC / 64; 
     8 CRC2 = '=' + tmpCRC % 64; 
  

• ToDo: describe checksum calculation verbaly

Implementations

• Sometimes its a lot more easy to look at code rather than reather than to look at Specifications/Documentation:
• uart.c in the Flight-Ctrl Firmware ( C )
• MKCommunicator.java from ["DUBwise"] ( Java / J2ME )
• mktool.cpp @ ["QMKGroundStation"] ( C++ )

• GroundStation ( LabView )

Links

• http://mikrokopter.de/forum/topic-1735-1.html ( german )

• CategoryCoding KategorieEnglish KategorieFirmware