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Ref.:
UoD_SpW-10X_
UserManual
Issue:
3.4
SpW-10X
SpaceWire Router
User Manual
Date:
11
th
July 2008
Preliminary
148
13.4 PARITY ERROR ANOMALY
13.4.1 Parity Error Action
A parity error on the SpaceWire link causes the link to be disconnected by the SpaceWire router. If a
packet is being received the packet is discarded and an error end of packet (EEP) is appended to the
end of the packet.
13.4.2 Parity Error Anomaly
The SpaceWire CODEC in the SpW-10X router detects a parity error and then resets the link but it
takes 167ns to reset the link after the parity error has been detected. During this time any data
characters, EOPs or EEPs received after the parity error will be placed in the receive FIFO. These
characters following the parity error are not removed from the receive buffer when the link is reset.
An example of this anomaly is shown in Figure 13-6.
Figure 13-6 Data after parity error anomaly
The number of characters added to the buffer depends on the input bit-rate: higher input bit rates
result in more received characters being appended to the buffer after the parity error. The maximum
time to reset the receiver after detecting the parity error is 167 ns. Therefore if no data characters are
input for 167 ns after the parity error no extra data characters are inserted to the receive buffer.
If the input link rate is below 24 Mbit/s the anomaly will not occur as the smallest data character, end
of packet marker which is 4 bits long cannot be decoded within 167 ns. Above 24 Mbit/s the number of
characters inserted in the buffer depends on the type of character, end of packet or normal data, and
the input bit rate. For example: at 100 Mbit/s a maximum of one received data character can be
added, 100 ns per data character.
If the parity error occurs on the last byte of the packet before the end of packet and the bit rate is
above 24 Mbit/s the error is not recorded by an error end of packet. The receive buffer detects the last
data character written to the buffer is an end of packet and therefore does not insert an error end of
packet to terminate the packet.
The operation is shown in Figure 13-7.