Atmel SpaceWire Router SpW-10X - Manual (Page 48)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
48
CLK
1 2 3 4 5 6 7 8 9 10 11 12
EXT_OUT_READ_Nx
EXT_OUT_DATAx
EXT_OUT_EMPTY_Nx
DATA1 DATA2 DATA4 DATA3
read
read
read
Figure 6-2 External port read timing specification
Reading of the External port is illustrated in Figure 6-2. When data is available in the External port
FIFO then it is placed on the EXT_OUT_DATA bus and the EXT_OUT_EMPTY_N signal is asserted
to signal to the external system that data is available. This is done synchronously to the SYSCLK
signal (e.g. clock cycle 2 in Figure 6-2). When it is ready the external system asserts the
EXT_OUT_READ_N signal synchronously with the SYSCLK signal (e.g. clock cycle 3) and the data is
then read out of the external port on the next rising edge of the SYSCLK (e.g. start of clock cycle 4). If
there is no more data available in the FIFO then the EXT_OUT_EMPTY_N is de-asserted once the
data has been read. If the FIFO contains more data to transfer then the EXT_OUT_EMPTY_N
remains asserted, the new data is placed on the EXT_OUT_DATA bus and the external system can
read it as soon as it is ready. The read access is ignored if there is no data available
(EXT_OUT_EMPTY_N is active).
6.2 TIME-CODE INTERFACE OPERATION
In this section the time-code interface operation is defined.
EXT_TICK_IN
SEL_EXT_TIME
EXT_TIME_IN
Time-code inputs
EXT_TIME_IN
used for time-code
Internal time-code
counter
used for time-code
Figure 6-3 Time-Code Input Interface
Time-codes can be generated by the router on request of the external system to which it is attached. A
time-code is generated whenever the router detects a rising edge on the EXT_TICK_IN signal as
illustrated in Figure 6-3. The value of the time-code to be transmitted is either taken from the inputs or
from the time-code counter inside the router. The time-code source used depends on the value of the