GR740-UM-DS, Nov 2017, Version 1.7
147
www.cobham.com/gaisler
GR740
13.2.15.1 Timer disabled
The incoming packet will wait indefinitely for the output port(s) to be ready if the data character timer
for an input port is disabled, unless the spill-if-not-ready feature is enabled for the packet’s address
(see section 13.2.10).
13.2.15.2 Timer enabled, but output port(s) not in run state
If the spill-if-not-ready feature (see section 13.2.10) is enabled, incoming packets are directly spilled
in case the output port(s) are not in run state. If the feature is disabled, however, the incoming packet
might be still spilled if the data character timer of the input port (together with the overrun timeout
RTR.PCTRL2.OR) is enabled and the timer elapses before the output port(s) enter run-state. In case
of group adaptive routing it is sufficient for one output port to enter run-state whereas in case of
packet distribution all output ports must enter run-state. Note that this even applies if the link-start-on-
request feature is enabled for an output port but the chosen timeout period is shorter than the time
required to automatically start the link interface.
13.2.15.3 Timer enabled, output port(s) in run-state but busy with other transmission
The input port’s data character timer will not start and the incoming packet will wait indefinitely until
the output port either becomes free or leaves run-state. If group adaptive routing is enabled for the
address of the incoming packet, the timer will not start if at least one output port of the group is in run-
state. If packet distribution is used, the timer will not start if all output ports of the group are in run-
state.
13.2.15.4 Timer functionality when accessing the configuration port
The timer functionality is basically the same for the configuration port as for the other ports. When a
command is received, the configuration port is the output port of the data transfer and when a reply is
sent, the configuration port is the input port of the data transfer. The differences between the configu-
ration port and the other ports are:
•
The configuration port can always accept data fast enough, which means that an overrun timeout
can never occur while a command is received.
•
The configuration port can always send data fast enough, which means that an underrun timeout
can never occur while a reply is sent.
13.2.16 Packet length truncation
Packet length truncation monitors the length of an incoming packet and increments a counter for each
received data character. If the counter reaches a value larger than the input port’s RTR.MAXPLEN
register and truncation is enabled for the input port (RTR.PCTRL.PL = 1), the rest of the packet is
spilled and an EEP is written to the FIFO of the output port(s). Each port has its own RTR.MAX-
PLEN register and counter in order to allow different maximum lengths for different ports.
Packet length truncation can also be enabled for port 0. In this case, it is the length of the RMAP /
SpaceWire Plug-and-Play reply packet that is monitored.
13.2.17 System time-distribution
The router supports system time distribution through time-codes, as defined in [SPW]. It comprises a
global time-counter register (RTR.TC) from which the latest received time-code can be read. Both the
SpaceWire ports and the AMBA ports support time-code transmission and reception. All incoming
time-codes update the RTR.TC register. If the incoming time-code has a time value which equals the
old RTR.TC value plus one (modulo 64), the time-code is forwarded to all the other ports. The time-
code is not sent out on the port on which it arrived. More details about the sending and receiving of
time-codes through the AMBA ports are given in section 13.4.3.
