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GR716-DS-UM, May 2019, Version 1.29
344
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GR716
culated increment value. The output of frequency synthesizer is used for enabling the increment of ET
counter. The increment rate of the ET counter and frequency synthesizer counter should be set accord-
ing to the system clock frequency. The ET counter increment rate is set by providing values to ETINC
bits in Configuration 2 register and frequency synthesizer counter is set by providing values to FSINC
bits in Configuration 1 register. The following table specifies some example ETINC and FSINC val-
ues for some frequencies. The below values are also obtained for Coarse time width 32, Fine time
width 24 and Frequency synthesizer width of 30. To calculate for other frequencies and configuration
refer the spreadsheet provided along with this document.
The following section describes the cores capabilities if it configured as initiator or target.
34.3.4 Initiator
An initiator is a SpaceWire node distributing CCSDS Time Codes and SpaceWire Time-Codes. It is
also an RMAP initiator, capable of transmitting RMAP commands and receiving RMAP replies.
There is only one active initiator in a SpaceWire network during a mission phase.
The initiator performs the following tasks
•
Transmission of SpaceWire Time-Codes
The SpaceWire Time-Codes are provided by this component and transmission of those codes to tar-
gets should be performed by a SpaceWire interface.
•
Transmission of CCSDS Time Codes through RMAP
•
Datation, time-stamping and latency measurement
34.3.5 Target
A target is a SpaceWire node receiving CCSDS Time Codes and SpaceWire Time-Codes. A target is
also an RMAP target, capable of receiving RMAP commands and transmitting RMAP replies. There
can be one or more targets in a SpaceWire network.
The target performs the following tasks
•
Reception of SpaceWire Time-Codes
The SpaceWire Time-Codes sent from initiator are received by SpaceWire interface and provided to
this component in target.
•
Reception of CCSDS Time Codes through RMAP
•
Qualification of received time messages (CCSDS Time Codes) using SpaceWire Time-Codes
•
Initialization and Synchronisation of received CCSDS Time Codes with Elapsed Time counter
available in this component
•
Datation, time-stamping and latency correction
34.3.6 Configuring initiator and target
The core is interfaced via an AMBA Advanced Peripheral Bus (APB) slave interface, providing a reg-
ister view that is compatible with the Time Distribution Protocol (TDP). The core must be configured
according to the requirement either as initiator or target.
•
Initializing initiator
Table 436.
Example values of ETINC and FSINC for corresponding frequencies
Frequency
ETINC
FSINC
50 MHz
0
360287970
250 MHz
0
72057594
33333333
2
135107990