COMMAND RANGING & TELEMETRY UNIT CORTEX
Is.Rev.
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Page 99
3.3.12.
Real-Time of Off-line Telemetry Server
3.3.12.1.
Telemetry Request
Real-time and off-line telemetry data are transmitted only on reception of a telemetry request from the Telemetry
Client. On reception of a telemetry request, the CORTEX CRT Quantum checks its validity and returns a
negative telemetry acknowledgment message (invalid request) or Telemetry Messages (valid request) to the
Telemetry Client.
The telemetry request specifies:
The telemetry
channel number
or storage area on the disk (TM-A to TM-H),
Frame mask
ing data (Virtual Channel extraction in CCSDS mode, etc…),
The amount of buffered telemetry data to transmit (see next section) for real-time telemetry
only,
The type of
data flow
: « single frame/block transmission » (a telemetry request is required
for each frame or block) or « permanent flow » or « permanent flow + dummy TM » (see
below).
Only in case of
request for off-line telemetry data
: number of telemetry files to transmit
or date of first and last frame or block to transmit.
Up to 24 simultaneous connections are accepted on the Telemetry port (all telemetry channels merged). In the «
single frame transmission » mode, it is not required to close the connection between two consecutive TM
packets. It is the client’s responsibility to ensure that the data acquisition rate by the host computer will avoid
losing telemetry data.
3.3.12.2.
Telemetry Buffers
Reconstructed telemetry blocks or frames are routed to the Telemetry port through a circular buffer in volatile
memory. The size of the buffer is configurable from 256 to 1024 frames or blocks (system configuration, not
reported to Monitoring Clients). Buffer management is ensured by two pointers:
The « write » pointer is incremented by 1 each time a frame or a block is written to the
buffer by the frame synchronizer,
The « read » pointer is incremented by 1 each time a frame or a block is transmitted to the
Telemetry Client. Incrementing rate for the « read » pointer is limited by the rate in writing
the frames or blocks to the buffer (obviously, a client cannot receive frames or blocks that
have not been yet stored into the buffer!).
At client’s connection, the « read » pointer is set to [« read » pointer - N], N being programmable from 0 (request
for immediate transmission of real time telemetry) to the maximum size of the buffer (the buffer must be emptied
before the CORTEX CRT Quantum starts transmitting real time telemetry).
If, for any reason, the acquisition rate by the Telemetry Client is lower than the production rate by the frame
synchronizer, then each time the « read » pointer is passed by the « write » pointer, the full amount of data
stored in the buffer is discarded.
