Atmel SpW-10X user manual Parity Error Anomaly, Parity Error Action

SpW-10X	Ref.:	UoD_SpW-10X_
SpaceWire Router		UserManual
	Issue:	3.4
User Manual
	Date:	11th July 2008

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.

Preliminary 148