AEROFLEX GAISLER
18
RT-SPW-ROUTER
Copyright Aeroflex Gaisler AB
June 2012, Version 1.2
can be disabled by setting the self addressing enable (SA) bit in the router configuration/status register
to 0. The reset value of this bit is set using a signal.
This also applies to group adaptive routing and packet distribution. When group adaptive routing is
enabled for an address a packet with that destination address will be spilt due to self-addressing only
if the packet is actually routed to the source port. That is if ports 1 and 2 are enabled for address 1 and
a packet with address 1 arrives and it is routed to port 2 the transfer will be performed normally. If it is
routed to port 1 and self-addressing is disabled it will be discarded.
For packet distribution the packet will always be discarded if the source port is included in the list of
destination ports since the packet will be sent to all destinations.
3.2.11.2 Link start on request
Ports can be configured to start automatically when a packet is waiting to be transmitted on it. This is
done by setting the LS bit in the router configuration/status register to 1. If the port link is disabled it
will override the start feature and the link will not start. The reset value of this bit is set using a signal.
This feature is only applicable for SpaceWire ports.
If the linkstart bit for the port is set the setting for the link start on request bit will have no effect. The
link will continue to be started until a ‘0’ is written to the linkstart bit of the port or if the auto discon-
nect feature is enabled (see next section).
3.2.11.3 Auto disconnect
If the link was started by the link start feature the auto disconnect feature can be enabled to automati-
cally stop the link if inactive during a timeout period. The auto disconnect feature is enabled by set-
ting the AD bit in the router configuration/status register. The reset value is set using a signal. This
feature is only applicable to SpaceWire ports.
The link will be disconnected under the following conditions. The link start on request feature is
enabled and the link was not in run-state when the packet arrived at the output port. Then the link will
be disconnected when the packet transmission has finished (output port free), the transmit FIFO is
empty, no receive operation is active and the timeout period has expired since the last of the require-
ments for disconnect (the ones listed here) became true.
3.3
SpaceWire ports
When a port is configured as a SpaceWire link it consists of a SpaceWire codec with FIFO interfaces.
All the configurable parameters for the link are accessible through the router configuration port (see
the register section for the configurable parameters).
3.4
FIFO ports
A port configured as a FIFO port contains one FIFO in each direction to/from the switch matrix.
3.4.1
Transmitter
The transmitter FIFO interface consists of the following signals: txfull, txafull, txwrite, txchar,
txcharcnt. Figure 2 illustrates the write operation. Note that txfull would only be asserted as illustrated
in the figure when txcharcnt is 4 if the FIFO size is 4 (which is not the case typically).
