AT7911E
6. Operating Modes
According to the different protocol formats expected for the operation of the AT7911E, two major
operation modes are implemented into the AT7911E. For each link channel the operation modes
are chosen individually by setting the respective configuration registers via the HOCI or via the
link.
6.1
Simple Interprocessor Communication (SIC) Protocol Mode
This mode executes the simple interprocessor communication protocol as described in the
chapter 13 of the 'SMCS332SpW User Manual'.
The following capabilities of the protocol are implemented into the AT7911E:
• Interpretation of the first 4 data characters as the header bytes of the protocol
• Autonomous execution of the simple control commands as described in the above mentioned
chapter
• Autonomous acknowledgement of received packets if configured
In transmit direction no interpretation of the data is performed. This means that for transmit pack-
ets, the four header bytes must be generated by the host CPU and must be available as the first
data read from the communication memory. EOP control characters are automatically inserted
by the AT7911E when one configured transfer from the communication memory has finished.
6.2
Transparent Mode (default after reset)
This mode allows complete transparent data transfer between two nodes without performing any
interpretation of the databytes and without generating any acknowledges. It is completely up to
the host CPU to interpret the received data and to generate acknowledges if required.
The AT7911E accepts EOP and EEP control tokens as packet delimiters and generates autono-
mously EOP or no EOP (as configured) marker after each end of a transmission packet.
The transparent mode includes as a special submode: Wormhole routing.
6.2.1
Wormhole routing
This mode allows hardware routing of packets by the AT7911E. It is a submode of the transpar-
ent mode. The AT7911E introduces a wormhole routing function similar to the routing
implemented in the SpaceWire router. Each of the three links and the AT7911E itself can be
assigned an eight bit address. When routing is enabled in the AT7911E, the first byte of a packet
will be interpreted as the address destination byte, analysed and removed from the packet
(header deletion). If this address matches one of the two other link addresses or the AT7911E
address assigned previously, the packet will be automatically forwarded to this link or the FIFO
of the AT7911E. If the header byte does not match a link address, the packet will be written to
the internal FIFO as well and an error interrupt (maskable) will be raised.
7. Fault Tolerance
The SpaceWire standard specifies low level checks as link disconnect, credit value, sequence
and parity at token level. The AT7911E provides, through the Protocol Processing Unit, features
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7737B–AERO–05/08
ATMEL [ ATMEL ]
