cx28560 Mindspeed Technologies, cx28560 Datasheet - Page 258

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

Buffer Controller FIFO Size Calculation
Figure E-3. Servicing a Normal Channel
Figure E-4. Worst Case Servicing of a Mid-range Channel
E-8
42 B
28 B
28 B
42 B
Between points (a) and (b), up to 84 bytes of data may accumulate (42 bytes between
each service).
The 42 Bytes comes from the following:
At (a) the channel FIFO contains initial bytes amount of data.
The extra bytes accumulated for the frame swapping only needs to be included in the
calculation once. This is because the next time the frame is swapped, the maximum
amount of time between the last time a service could have taken place and the first
service of the frame is one step size. Hence, the amount of data accumulated in the
buffer is reduced, and the next time the frame is swapped, the extra accumulated data
will be stored in the freed bytes from the previous over-allocation.
Figure E-3
Note the above is an absolute worst case because the first time the channel is serviced,
it is serviced once and then must wait 42 bytes to be serviced twice in succession.
Figure E-4
28 B
42 B
Due to the mid-range, in the worst case, each channel that uses the mid range
receives (x + x / 2) = 3x / 2 services in a frame according to its BW, (while x is
the number of services for the lower closest full range). The number of bytes
received per frame is 28 B * 3x / 2 = 42 B * x. X services are guaranteed to
receive service with constant slots between them; thus, the worst distance
between two services is 42 bytes.
illustrates servicing a mid-range channel.
illustrates servicing a normal channel.
Mindspeed Technologies™
28 B
42 B
Advance Information
28 B
42 B
28 B
42 B
28 B
42 B
28 B
42 B
CX28560 Data Sheet
28560-DSH-001-B
28 B
42 B
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