User manual

26
6.5.2 Group Adaptive Address Bits
Bits [9:5] are used when Group Adaptive has been enabled and the port selected by the Primary Logical
Address Bits is busy. If group adaptive routing is not enabled and port selected by the Primary Logical
Address Bits is busy, the packet waits until the selected port is free.
6.5.3 Enable Header Delete Bit
Bit [10] is used to enable the header delete function for the port selected by either the Group Adaptive
Address bits or the Primary Logical Address Bits. Whenever this bit is set high, the router deletes the header
before sending the packet out of the requested transmit port.
6.5.4 Enable Group Adaptive Bit
Bit [11] is used to enable the Group Adaptive function on the router. Setting this bit high tells the router to
use bits [9:5] for the port select in the event the port select for the Primary Address Bits is busy.
6.5.5 Unused Bits
Look up table bits [14:12] needs to be set to 0x00. In order for the parity bit to be correct all three unused bits
need to contain 0’s. If these bits are set to something other than 0x00, the parity calculation will not be the
same as what the router is calculating.
6.5.6 Parity Bit
A Parity Bit is included for each lookup table location. The parity is even. When the header byte is decoded
and falls between address 0x20 and 0xFF, a lookup table address will be retrieved by the lookup table.
Again, parity will be calculated by adding the number of ones that are contained in the previous 8-bits data. If
the total number of 1's in bits added together is odd, the parity is odd parity. And if the number of 1's in bits
added is even, the parity is even parity. The current parity bit will then be compared to the calculated parity
and if they are not the same, the packet will be read out of the receive FIFO. This is commonly referred to as
"Spilling the Packet". Additionally, the Parity Error Register will be incremented.
Parity error register is different from the previously discussed SpaceWire parity. The parity error register is
based on the data in the lookup table. Please see ECSS-E-ST-50-12C for more information regarding parity.
6.5.7 Look up table configuration Example 1
Assume the user wants to write to the configure look up table address 0x0020 to contain addressing to send
out port 1. Meaning if a packet is received with logical address bytes 0x0020 it will be routed out port 1 of
the router. The user is in communication with the router via the HOST port or port 5.
The user will have to use the write configuration protocol into port 5 (HOST Port) of the Primary router to
set up look up tables.
SpaceWire Port 1
SpaceWire Port 2
SpaceWire Port 3
SpaceWire Port 4
HOST Port
Figure 14. 4-Port Router configuration for the look up table access and configuration example