MA28140 Datasheet, PDF (12/72 Pages) Dynex Semiconductor – Packet Telecommand Decoder

MA28140
THE FARM-1 PROCESS DESCRIPTION
At the user end of the FARM-1 process the TC segments
are delivered as a buffer of accepted data. No distinction is
made between a TC segment delivered by means of an AD
frame and one delivered by a BD frame. However, the
management of the common FARM-1 back end buffer is
affected as follows:
• BD Frames:
When a frame of this type is accepted by the FARM-1, the
TC segment it contains shall be placed in the back end buffer
of the FARM-1 even if this buffer still contains data (partially
read or not ) in which case this data will be erased, an abort
signal sent to the Segment Layer to signal the erasure and the
new data signalled as arrived. This implies an Event E10.
• AD frames:
When a frame of this type is accepted by the FARM-1, the
TC segment it contains is placed in the back end buffer of the
FARM- 1 only when the buffer is available (empty). If the buffer
still contains data, the newly arrived frame is discarded
(erased) as shown by the FARM-1 state table (Event E2 in
table 1).
The definitions used in the FARM-1 State Table are listed
below:
• “Valid frame arrives” means that the Legal Frame
Validation Sublayer has placed a legal frame in the front-end
buffer. If the frame is a data frame (AD or BD) and if the FARM-
1 accepts it, the back end buffer is allocated for the data.
• “Accept” for an AD frame is subject to a buffer available
signal. When no back end buffer is available (Event E2) the
frame is discarded. The data is then made available for the
Authentication Layer, or the Segmentation Layer if
Authentication is disabled.
• “Accept” for a BD frame means that the TC segment is
placed in the back end buffer even when this buffer still
contains data, in which case this previous data is erased
(event E10). The Wait concept does not apply to BD frames.
The data is available for the Authentication Layer, or the
Segmentation Layer if Authentication is disabled.
S t a t e Na me
Main Feature of State
State Number
OPEN
Normal state to
accept frames
(S1)
WAI T
Wait Flag is on
S(2)
LOCKOUT
Lockout Flag is
on
S(3)
Event Conditions
N(S)=V(R)
A buffer is
available for this
frame
Event
Numbe r
E1
OPEN
Accept frame,
V(R):=V(R)+1R
etransmit
Flag:=0
WAI T
Not applicable
LOCKOUT
Discard
(S1)
Valid AD frame
N(S)=V(R)
No buffer is
E2
Discard,
Discard
arrives
available for this
Retransmit
frame
Flag:=1,
Wait Flag:=1
N(S)>V(R) and
E3
N(S)<V(R) +PW-1
i.e. inside ^positive
part of sliding ^{window and >V(R)}
N(S)<
(S2)
Discard,
Retransmit
Flag:=1
(S1)
(S2)
Discard
(S2)
(S3)
Discard
(S3)
Discard
(S3)
Table 1: The FARM-1 State Table
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