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5.2.9 Router Configuration Protocol
The user may want to access to the configuration and status registers. Access to these registers can be accomplished
though any one of the four SpaceWire ports or the External Port. The default configuration is for all ports to be
configuration ports. If one or more ports are set up to be configuration ports, only one configuration command should
be sent at a time.
5.2.9.6 Configuration Ports
If multiple ports are set up as configuration ports and more than one configuration command is
being sent within the router, the configuration packets will be corrupted. The first byte of data with
value 0x00 received by any router port after reset or an EOP/EEP initiates a configuration
transaction. (ECSS-E-ST-50-12C). Configuration transactions allow access to the lookup tables,
configuration registers and status registers. The packet protocols for configuration reads and writes
are specified in the following sections.
5.2.9.7 Configuration Write
A configuration write packet loads a 16-bit data word to the specified 16-bit address location in the
configuration memory space. A configuration write packet begins with zero (0x00) or can contain
additional router address bytes, followed the final destination address byte set to zero. A
Configuration Write packet is shown below.
Next, the router ID byte should be set to the value in the receiving router ID register. The Packet
Type byte should be set to Write (see table 6.), followed by the address least significant byte, the
address most significant byte, then the data least significant byte and the data most significant byte.
The last byte before the end of packet (EOP) will be the arithmetic Checksum value, which is an
arithmetic sum of the final destination address, the router ID, the Packet Type, the Address and Data
bytes. If the checksum value does not match, the command will not be executed. If the packet has
less than eight (8) bytes or the Checksum value is not the last byte, the command will not be
executed. (ECSS-E-ST-50-12C).
5.2.9.8 Configuration Read
The Read packet will read a number (Count) of 8-bit data values from consecutive 16-bit address
locations and transmit the data to the return location specified. This packet begins with zero or more
hardware or logical address bytes followed by the final destination address byte set to zero.
Next, the router ID byte should be set to the value in the router ID register, unless the router ID is
being read. The Packet Type byte should be set to Read, (0x01 or 0x02) followed by the address
least significant byte, the address most significant byte, the word count byte, and one or more return
path address byte(s). The order of the return path address bytes are to read in the order they are
received.
That is to say, the first return path address byte will be the path out of the first router with
subsequent bytes to be used for the next layers of routers. The last byte will be the checksum value,
which is an arithmetic sum of the destination address, router ID, packet type, address bytes, data
bytes and return path bytes. If the checksum received does not match the calculated value, an error
end of packet will be sent to the return address. The word count byte must be greater than zero. A
value of zero causes the command to not be executed. The return address path must contain one or
more bytes and the first header byte must not be zero; otherwise, the command will be considered
invalid and not be executed. The following figure shows the bytes required for a Read Packet
Command.
Figure 9. Configuration Write Command
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