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TSS901E

Rev. C – 24-Aug-01

via one of the three links. This allows to use the TSS901E in systems without a local

controller (µController, FPGA etc.). Since the HOCI is no longer used in this operation

mode, it is instead available as a set of general purpose I/O (GPIO) lines.

Wormhole Routing

The TSS901E introduces a wormhole routing function similar to the routing implemented

in the ST-Microelectronics C104 routing switch. Each of the three links and the

TSS901E itself can be assigned an eight bit address. When routing is enabled in the

TSS901E, 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 TSS901E address assigned previously, the packet

will be automatically forwarded to this link or the FIFO of the TSS901E. 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.

PPU Functional

Description

Since the Protocol Processing Unit (PPU) determines a major part of the TSS901E func-

tionality, the principal blocks of the PPU and their function are described here. This

functionality is provided for every DS link channel of the TSS901E.

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Protocol Execution Unit: This unit serves as the main controller of the PPU block.

It receives the tokens from the DS macrocell and interprets (in protocol mode) the

four header data characters received after an EOP1/EOP2 control character. If the

address field matches the link channel address and the command field contains a

valid command then forwarding of data into the receive FIFO is enabled. If the

command field contains a "simple control command" then the execution request is

forwarded to the command execution unit.

The protocol execution unit also enables forwarding of header data characters to

the acknowledge generator and provides an error signal in case of address mis-

match, wrong commands or disabled safety critical "simple control commands".

The protocol execution unit is disabled in "transparent" or “wormhole routing” opera-

tion mode.

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Receive, Transmit, Acknowledge: The transmit and receive FIFOs decouple the

DS link related operations from the TSS901E related operations in all modes and

such allows to keep the speed of the different units even when the source or sink of

data is temporarily blocked.

In the protocol mode a further FIFO (acknowledge FIFO) is used to decouple send-

ing of acknowledges from receiving new data when the transmit path is currently

occupied by a running packet transmission.

•

Command Execution Unit: This unit performs activating resp. deactivating of the

CPU reset and the specific external signals and provides the capability to reset one

or all links inside the TSS901E, all actions requested by the decoded commands

from the protocol execution unit.

The unit contains a register controlling the enable/disable state of safety critical

commands which is set into the 'enable' state upon command request and which is

reset after a safety critical command has been executed.

The CPU reset and the specific external signals are forwarded to the Protocol Com-

mand Interface (PRCI).