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

'#'

'a'+ Addr

'V','D' etc

"modified-base64"

variable

variable

'\r'

Commands

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

Include(en/SerialCommands)

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

    • /!\ 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 )

  • VibrationTest ["en/VibrationTest"] (Python)

Links