Atmel AT7910E Uživatelský manuál stáhnout pdf (Strana 6)

AT7910E [DATASHEET]

7796G AERO 02/13

1.5 Routing control logic and crossbar

The routing control logic is responsible for arbitration of output ports, group adaptive routing and the crossbar switching.

Arbitration is performed when two or more source ports are requesting to use the same destination port.

A priority based arbitration scheme with two priority levels, high and low, is used where high priority packets are routed

before low priority packets. Fair arbitration is performed on packets which have the same priority levels to ensure each

packet gets equal access to the output port.

Group adaptive routing control selects one of a number of output ports for sending out the source packet.

1.6 Time Code Processing

An internal time-code register is used in the router to allow the router to be a time-code master or a time-code slave.

In master mode the time-code interface is used to provide a tick-in to the SpaceWire routing causing time-codes to be

propagated through the network. Two modes of time master operation are supported, an automatic mode where a time-

code is propagated on each external tick-in and a normal mode where the time-code is propagated dependent on the

external time-in signal.

In time-code slave mode a valid received time-code, one plus the value of the router time-code register, causes a tick-out

to be sent to the SpaceWire links and the external time-code interface. The time-code is propagated to all time-code ports

except the port on which the time-code was received. If the time-code received is not one plus the value of the time-code

register then the time-code register is updated but the tick-out is not performed. In this way, circular network paths do not

cause a constant stream of time-codes to be sent in a loop.

1.7 Control/Status Registers

The control and status registers in the SpaceWire router provide the means to control the operation of the router, set the

router configuration and parameters or monitor the status of the device. The registers are accessed using RMAP

command packets received by the configuration port.

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Atmel AT7910E Uživatelský manuál Strana 6