cx28560 Mindspeed Technologies, cx28560 Datasheet - Page 260

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

Buffer Controller FIFO Size Calculation
E.5.2.2
Figure E-5. Worst Case Servicing of a Mid-range Channel
E.5.2.3
E.5.2.4
E-10
Servicing
A series of 56-byte messages may cause the amount of data in the channel’s FIFO to
reach a steady state of FULL. This is acceptable because nothing can be done to tip
the steady state in the direction of overflow, and eventually the stream of 56-byte
messages will either change to different size messages, or the channel will be
deactivated.
So now assuming that either the messages are shorter (worst case 40-byte messages,
or that they are longer—now worst case is 57-byte).
Figure E-5
distance apart).
Servicing of a mid-range channel can be seen as repetitions of the shaded grey area
above; i.e., every 3 services plus 3 fillings the cycle is repeated.
Hence, if after 3 services and 3 fillings there is less data than at first, it could be on the
way to a convergent solution (not least since bandwidth out > bandwidth in).
57-Byte Messages
Reach end of first white area—after that is repetitions.
Start position (takes into account flags):
Since start with both less data and less FIFO bytes, can assume convergence.
Though minimum buffer required is 180 bytes to take into account state (f).
Last Bit (Byte)
Since during the service of a channel (20 cycles), a fast channel can accumulate a byte
which in turn could take an extra row in the FIFO, an extra 4 bytes of space must be
added to the maximum calculated above.
This gives a buffer space of 184 bytes per channel, or total of 368 KB.
a
b
c
d
e
f
g
h
illustrates worst case servicing of a mid-range channel (services maximum
Mindspeed Technologies™
56, 1, 56, 1, 24
32 bytes out
42 bytes in
1, 32 bytes out
42 bytes in
1 byte out
42 bytes in
56, 1 bytes out
42 bytes in
Advance Information
≥
≥
≥
≥
≥
≥
≥
≥
1, 56, 1, 24
1, 56, 1, 56, 1, 8
1, 56, 1, 8
1, 56, 1, 50
56, 1, 50
56, 1, 56, 1, 35
56, 1, 35
56, 1, 56, 1, 20
CX28560 Data Sheet
≥
≥
≥
≥ 92, 66
≥
≥
≥
≥
≥
28560-DSH-001-B
168, 140
108, 82
160, 123
136, 108
128, 107
180, 149
112, 92
164, 134
101302_024