cx28560 Mindspeed Technologies, cx28560 Datasheet - Page 259

• Manufacturer Part Number: cx28560
• Description: Hdlc Controller
• Manufacturer: Mindspeed Technologies

CX28560 Data Sheet
E.5.2
E.5.2.1
28560-DSH-001-B
Calculation of Step Size Between Services
The slots per channel are given with gaps, according to the channel BW. The gap size
represents the time at which the channel accumulates 28 bytes of data in its specific
BW. The 28 bytes that may accumulate is the amount of data that, after expansion,
will use the 32 bytes of data in a burst. The expansion is due to the fact that a message
length is not optimal to the 56-byte bursts. It may take 2 bursts to send a 56-byte
message. The 2 bursts BW is 112 bytes, so the ratio between the original message size
to the actual BW allocated for it is 112 / 56 = 2. Example: the accumulation of 28
bytes at a 52 Mbps channel takes 4307 ns (431 clock cycles). A fast channel must be
serviced every such period. It means that a fast channel is to be serviced every 431 /
20 = 21.55 slots -> 21 slots.
Starting Position
Initial bytes + extra bytes due to missed service + extra bytes due to swapped frame
Initial bytes form one (or less fragment).
Extra bytes are 42 bytes each—a total of 84 extra bytes
Number of fragments available to be transferred (not including initial fragment) = N
Each fragment contains x bytes of data and y bytes of overhead (headers, last bytes)
where:
x + y = initial bytes
In general, x
This is only not true when a full fragment is followed by a shorter end of message
fragment. In this case:
There are 84 bytes entering the block. These can be divided as follows:
(note in worst case x
Hence, max N = 4.
Sum (x
Sum (y
Hence, initially buffer contains:
Initial bytes + Sum (x
MinStepSize
1
1
: x
: y
4
4
)
)
Mindspeed Technologies™
≥
≤
≤
40.
84
4 * max y = 32
=
≤
SystemClock
--------------------------------- -
2
TimeperSlot
Advance Information
1
60
= 0 at start of “other”)
: x
4
0 ≤ x ≤ 56
4 ≤ y ≤ 8
x
x + y ≤ 60
x
X
X
X
) + Sum (y
1
1
2
2
2
+ … + x
+ x
+ all singular xs ≥ x
+ all doubles ≥ x
+ single/double mix ≥ x
2
≥ 56
1
×
: y
N
FragmentSize
------------------------------------ -
≤ 84
4
)
≤
60 + 84 + 32 = 176 bytes
2
2
+ (x
2
Buffer Controller FIFO Size Calculation
×
+ 3 * x
1
2
----------------- -
bitrate
+ x
+ x
8
2
3
) + x
+ x
3
≥ N = 4
1
1
≥ N = 4
≥ N = 3
E
-
9