MA28140 Datasheet, PDF (41/72 Pages) Dynex Semiconductor – Packet Telecommand Decoder

MA28140
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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