pef20320 Infineon Technologies Corporation, pef20320 Datasheet - Page 218

• Manufacturer Part Number: pef20320
• Description: Multichannel Network Interface Controller For Hdlc With 32 Channels
• Manufacturer: Infineon Technologies Corporation

User’s Manual
Applying these values to the equations yields the following:
When the packet size is much larger (256 bytes or larger), the bus occupancy decreases
to less than 4%. Conversely, sending very small frames (4 bytes), causes bus
occupancy to increase to over 11%. This is primarily due to the increased descriptor
processing per packet.
5.3.2
The previous discussion shows bus occupancy to be very low, even when a MUNICH32
is processing 32 channels of receive and transmit data. There is another system
consideration of bus occupancy that must be examined. When a MUNICH32 channel
has no data required for transmit, the channel must be temporarily (or permanently)
stopped. There are several methods that may be used to stop the transmission.
1. The first method involves executing a channel command with TH = 1 (reactivation of
2. A second method is based on statistical knowledge of the frequency of transmitted
the channel requires a new channel command with TH = 0). This method places the
transmit channel on hold and prevents any further accesses of the memory for this
channel.
frames. If frames are transmitted without shared flags and if the average number of
interframe time fill characters can be determined, the MUNICH32 can be programmed
to suppress poll sequences. By setting FNUM in the Tx descriptor to a value (n)
greater than 0, the MUNICH32 will transmit n + 1 idle characters after the end of the
current frame. During this period of interframe time fill, the MUNICH32 will not poll the
Tx descriptor. As an example, if it is determined that 5 idle characters typically occur
between frames, FNUM can be set to 4. At the end of the current frame, 5 idle
characters will be transmitted (625 s. on a DS0 channel) before the next frame is
transmitted and no polls of the Tx descriptor will occur during that time.
Time used to access memory
= {([6 + (1 + 7)]
= {(14
= {864}
= 231.9 s.
Time used to send data
= ((4 + 32)
= 36
= 4500 s.
Bus occupancy = 231.9 s/4500 s = 5.1%
Bus Occupancy for Idle Tx Channels
125 s.
32) + (13
268.4 ns
8/8)
32) + ([5 + (1 + 7)]
125 s.
32)}
1.1
244 ns
218
32)}
(1.1)
4
61 ns
Application Notes
PEB 20320
01.2000