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Guidance system
Netserver program
Attitude and
guidance control
A/D Filter
TCP/IP
Send
Remote
Computer
Data
acquisition
card
TCP/IP
Listen
File logger
Rocket Ignition
and thrust control
Startup
Rocket Motor
Figure E.2: Framework communication flow.
E.4.6 Remote command relaying
We are now ready to go back to the Listen thread command interpreter. The case
ID_START_AD looked like this:
case ID_START_AD:
MsgSendPulse(chid_filt,pulseprio,COMMAND_PULSE_CODE,ID_START_AD);
MsgSendPulse(chid_send,pulseprio,COMMAND_PULSE_CODE,ID_START_AD);
break;
The exact same pulse is being sent to two different channels, one to chid_filt (Filter thread),
and one to chid_send, (Send thread).
Besides the connection identifier, each pulse has a priority, a pulse code and a value to
be entered in that order when MsgSendPulse() is issued. The COMMAND pulse code is used
in order to tell the particular thread that a remote command has been received (or locally
issued). The command type is passed in the value field of the MsgSendPulse() function. Note
that the ID List macro is reused here. Thus the ID List defined in IDList.h is used both for
network communication as well as internal communication. Other pulsecodes used are
defined in the file pulsecodes.h.
E.4.7 Sending measurement data over the TCP/IP connection
When an ID_START_AD command pulse is received by the Send thread, it starts sending
measurement data to the remote client. In the current implementation it sends measurements
every second, controlled by a timer.
The thread uses a wrapper function to add a measurement packet to the current TCP/IP
send buffer. The essential code is found below:
pthread_rwlock_rdlock(&ad_data.rwl);
nsend+=addAnalogData2Buffer(&ptr,ID_CHAN0,ad_data.channel[0]);
nsend+=addAnalogData2Buffer(&ptr,ID_CHAN1,ad_data.channel[1]);
pthread_rwlock_unlock(&ad_data.rwl);
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