Atmel SpaceWire Router SpW-10X - Manual (Page 47)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
47
6. INTERFACE OPERATIONS
This section describes the operation of the external FIFO port, time-code interface and status/power
on configuration interface.
First a note on the terminology used: Signals are given a name (e.g. EXT_IN_FULL) and a logic level
(e.g. _N). The term asserted is used when the signal state reflects the signal name e.g. EXT_IN_FULL
is asserted when the external input FIFO is full. The term de-asserted is used when the signal state is
the inverse of the signal name e.g. EXT_IN_FULL is de-asserted when the external input FIFO is not
full. The logic level when a signal is asserted is indicated by the logic level extension to the signal
name. If there is no extension then when the signal is asserted it is logic 1 (high). If the _N extension
is present then when the signal is asserted it is logic 0 (low). For example, EXT_IN_FULL_N asserted
means that the physical signal is logic 0 (low) when the external input FIFO is full.
6.1 EXTERNAL PORT INTERFACE OPERATION
In this section the external port interface operation is described.
CLK
1 2 3 4 5 6 7 8 9 10 11 12
EXT_IN_FULL_Nx
EXT_IN_DATAx
EXT_IN_WRITE_Nx
DATA EOP DATA DATA
Figure 6-1 External port write timing specification
The operation of the External port during write operations starts with the EXT_IN_FULL_N signals
being de-asserted (going high) by the router (at clock cycle 2 in Figure 6-1) to indicate to the external
system that the router has room for more data and is ready to receive it through the External port. The
External system then puts data onto the EXT_IN_DATA data lines and asserts EXT_IN_WRITE_N
(goes low) to transfer data into the External port on the next rising edge of SYSCLK. As long as there
is room for new data (EXT_IN_FULL_N is de-asserted (high) the writer access is performed as long
as EXT_IN_WRITE_N is asserted (low). If no room is available the write access is ignored (cycle 9
and 10 in Figure 6-1) and will be performed when room has become available if EXT_IN_WRITE_N is
still asserted (low). Therefore the data (EXT_IN_DATA) must be valid at that time.