MA28140 datasheet(41/72 Pages) DYNEX

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5.8 EXTERNAL AUTHENTICATION INTERFACE

This interface is provided to connect the PTD with an

external Authentication Unit. The PTD allows the external AU

to access the data buffer (described in section 5.7) of the RAM

in order to process a TC segment which is to be authenticated.

The interface is composed of the following signals:

• AUDIS: (input) This signal functions as for the internal

AU, disabling the authentication unit.

• AUEXT: (input) This signal indicates the use of an

external authentication unit.

• AUST: (output) This signal indicates that a TC frame

has been received and must be authenticated. In this

case, AUST is activated a few clock periods after the

deactivation of the DECOD output indicating the end of

the tail sequence of the frame.

• AUBUF: (output) This signal indicates to the external AU

which RAM buffer is the back-end buffer containing the

TC segment to be authenticated.

• BRQN: (input) This signal is the bus request to read or

write the buffer from the external AU. It is activated for

each external access to memory.

• BGRN: (output) This signal is the acknowledge of the

PTD to BRQN; the PTD will then tristate its signals

connected to the RAM (RAMCSN, ROMCSN, LACCS,

RWN, LADR and LDAT). The LACK input has no effect

when BGRN output is asserted.

• AUEND: (input) AU result validation. This signal

indicates the end of the external authentication process

and validates the AUR signal.

• AUR: (input) AU result signal. This signal indicates that

the received TC frame is authorized or non authorized at

the rising edge of AUEND.

• AUTSL: (input) AU tail length select signal. This signal

allows definition of the length of the AU tail as follows:

- AUTSL = 0: The length of the AU tail shall be 9

octets. In this case the 9 last octets of the segment

authenticated by the external AU will be deleted by

the PTD before transferring the segment to the

application.

- AUTSL = 1: The length of the AU tail shall be 0

octets. In this case all octets of the segment

authenticated by the external AU shall be transfered

to the application.

• AUSBUF: (output) This signal indicates which AU Status

buffer the external AU must update.

• FARBUF: (output) This signal indicates which FAR

status buffer the external AU must update (the external

AU shall update only the bits 28 through 30 of the FAR

status).

The external AU process starts upon receipt of the rising

edge of the AUST signal, which is asserted by the PTD until

the AUEND input is asserted indicating that the external AU

process is finished. The result of the external authentication is

given by the AUR signal (set to 1 for a valid authentication).

The total duration of the external AU process plus the duration

of the MAP output (if it exists) must be smaller than the

duration of the next frame to arrive, measured from the start of

the frame to the end of the last valid codeblock. A longer

duration may lead to a rise of the FARMB WAIT flag. The result

must be given to the PTD before the end of the last valid

codeblock of the next frame to arrive, so as not to lock the

back-end/front-end buffer toggling mechanism, and the FAR

buffer management of the next frame.

The external AU can also write the AUS status in the local

RAM, in the buffer number given by the AUSBUF output. The

PTD locks the toggling mechanism of the AU status buffer

while AUST is high in order to prevent data corruption. The

external AU can also write bits 28 to 30 of the FAR status by

writing the fourth octet of the FAR status in the local RAM, in

the buffer number indicated by the FARBUF output. A similar

mechanism locks the toggling of the FAR buffer when the

AUST output is high. The AUS and FAR buffer update can

start when the PTD activates the AUST output and shall be

completed when the application asserts the AUEND signal.

The local memory interface provides a bus arbiter fault timer.

This timer is enabled when BGRN signal is active and reset

when BRQN signal is inactive. If a reset does not occur within a

minimum of 32 Tck and a maximum of 64 Tck (8 to 16

µs at 4

MHz), the BGRN signal is forced to inactive state. The

functional timings corresponding to this interface are given in

section 8.2.

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