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uMCPIno

uMCP Ino - is a free view on old (but still good!) DEC's DDCMP protocol.

  • a lightweight (only 6 extra bytes for data packets and 4 bytes for control packets)
  • byte-oriented
  • point-to-point
  • with handshake
  • with Nagle's algorithm
  • pipelining
  • integrity control
  • guaranteed packets ordering
  • and guaranteed delivery

In the Arduino-compatible implementation, there are some limitation due to memory size:

  • the packet size is limited to 64 bytes
  • the number of sent and unacknowledged packets is limited to 8
  • the number of packets to be send in pipelining mode is limited to 4

Message framing:

Control Header

Offset, bytes Item Size, bits
0 SIGN = 0xAD 8
1 PTYPE 8
2 TCNT 4
2 RCNT 4
3 HCHK 8 
if PTYPE == uMCP_PTYPE_DTA || PTYPE == uMCP_PTYPE_DTE

Data block

Offset, bytes Item Size, bits
4 DCNT 8
.. DATA 8 * DCNT
5 + DCNT DCHK 8 
endif

There are two types of nodes in the protocol:

  • Selected by default (Master node)
  • And unselected by default (tributary node)

A node can only send data messages when its SELECT flag is set to true

The main differences between Master and Tributary nodes are:

  • a master node has SELECT flag is set to true by default
  • a tributary node should return the SELECT flag as soon as it transmits all the data to be transmitted
  • if for some reason a master node doesn't receive the SELECT flag, it regains it by timeout

All control messages transfer the SELECT flag.

How to test?

  • Program your Arduino board with uMCPInoNode sketch
  • Connect your Arduino board with your PC via USB-UART converter
  • On your PC, run the uMCPIno Test application
  • Open Port monitor in Arduino IDE
  • Connect the uMCPIno test application to the USB-UART converter port
  • Now, to establish uMCPIno connection you can reset your Arduino board or press "START" button in the application.

Here some screenshots:

uMCPIno autostart on board power-on:

Example of handling with temporary dead line:

How to use?

  • if you want to use a standalone Arduino board as a uMCP-converter, when you put some data to it, and want it to be safely transferred to another uMCP Node, use uMCPIno.ino sketch. It supposed to use 2 serial ports - one to send and receive data bytes, and another to use as uMCP line (it can be Bluetooth, RF, or even underwater acoustic link).
  • if you want to embed the uMCPIno protocol to your project, you can use the uMCPInoNode.ino sketch. In this case you should change the sketch's code:

    1. To send data over uMCPIno link use the function:
      bool uMCPIno_SendData(byte* dataToSend, byte dataSize); where:
      dataToSend - a byte buffer to send
      dataSize - size of the buffer

    2. Before sending data, check if there is enough space in tx buffer:
      bool uMCP_IsCanSend(byte dataSize);
      where:
      dataSize - number of bytes to send

    3. To analyse the received data:
      The received over uMCP link data is stored in a ring buffer il_ring.
      The amount of received bytes is stored in il_Cnt
      The read pointer is in il_rPos.
      To perform the analysis of the received data, put your code in function:
      void USER_uMCPIno_DataPacketReceived();
      It fires when new data packet has been received from a remote node over uMCP line

    4. If you need to be informed, when the tx buffer is empty, put your code in function:
      void USER_uMCP_OnTxBufferEmptry();
      it fires when all sent messages has been acknowlegded by the remote node