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DCN Next Generation Open Interface Release 2.4 General

en | 19

Bosch Communications Systems | 2007 February | SRS_INF | Du010933

ACK and NAK packets follow the general data packet format without the message

information. The ACK and NAK header formats are described in §4.1.2.1.

⇒ A message is expected to be sent as one block. The CCU checks if each byte is received

within 50 ms of the previous byte. If not, a NAK-packet will be sent.

⇒ Upon reception of a NAK-packet the last transmitted message is resent again.

⇒ Each message includes a sequence number. The receiver may use this sequence to

order the messages received.

⇒ When no ACK-packet is received within 2 seconds after completion of the transmission

the packet will be retransmitted. A total of 2 retransmissions will be done before the

transmission of the packet will be cancelled.

⇒ Connection check is done using heartbeat (see §4.1.2.4.4). Any packet received is seen

as a valid heartbeat. When a heartbeat time-out occurs, communication will be stopped.

All pending packets/messages will be discarded.

On the CCU the application will be notified that the communication with the remote

controller is lost.

⇒ Communication parameters can be set using the special message type

MDSC_COMMUNICATION_PARAMS (see §3.2.4)

Restrictions:

∗ After sending a message the system waits for the acknowledge. This decreases the

throughput of the communication.

4.1.2.1 Header format

The header format has the following layout:

Escape Headertype Sequence

Defined as a structure definition:

typedef struct

{

BYTE byEscape; // fixed constant value 0xC8

BYTE byHeaderType;

BYTE bySequence;

} RSMT_HEADER;

where:

byEscape Escape byte used for recognition of the header. This escape

byte forms together with the header type a unique combination

and defines the purpose of the packet.

More information about the escape byte can be found in

§4.1.2.3.

byHeaderType Type identification of the packet. This value defines the purpose

of the packet. The different header types are described in

§4.1.2.1.1.

bySequence Sequence information where the packet is acting on. The usage

of this sequence number is explained in §4.1.2.1.1.

As shown in the structure definition the header has a fixed length and forms a leader to

recognise the start-point of a packet. The sequence number holds a unique (Modula 128)

number.

4.1.2.1.1 Packet type definitions

The ‘Full’ feature protocol knows several header types, which are used to acknowledge

messages transmitted. The following header types are defined:

‘$’ The packet holds message data. The total packet format is as described in

§4.1.1. The sequence number passed in the header is used to identify the

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