Echelon LonTal Stack - Manual (Page 55)

LonTalk Stack Developer’s Guide 43
Value Type Description Uplink /
Downlink
4 CpMsgAck The Serial MIP is entering the
ready-receive state. This is the Serial
MIP’s response to the CpMsgReq.
U
5 CpMsgReject An attempt to transfer a message
downlink is rejected because of a lack of
buffer space.
This code packet will be a response to a
downlink CpMsgReq code packet or a
response to a CpMsg without the
CpMsgReq being sent.
This code indicates that the offered
downlink traffic is more than the Serial
MIP can handle (it has no more APP or
NET output buffers).
Upon receiving this code, the device
driver should repeat the message send
process until it succeeds.
U
6 CpNiCmdShort Sends a single byte local network
interface command. The command is
stored in the Param Data field.
U/D
7 CpResync This command is sent by the host to start
a new session with the Serial MIP. When
received it will reset the transmit and
receive sequence numbers to zero so that
any subsequent sequence numbers will be
accepted rather than rejected.
This command is also a good way to
establish that communications are
functioning with the Serial MIP.
The Serial MIP always responds to this
command with a CpNull packet, so the
host can determine that the serial link is
not simply echoing data.
D
Notes:
• Use symmetrical timeouts on the host processor. There is an inter-byte
timeout on the client side of 40ms when receiving either a code packet or
a message body. There is a timeout of 250ms when waiting for the start
of a downlink message CpMsg following a CpMsgReq / CpMsgAck
sequence.