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