AAL2 Implementation
MPC885 PowerQUICC Family Reference Manual, Rev. 2
44-28
Freescale Semiconductor
44.10.5 Initialization of Timer CU Mechanism (Optional)
If the built-in Timer CU mechanism is used, the host should do the following:
•
Initialize the TIMEP field in the RCCR
•
Set the TIME bit in the RCCR
•
Define the wait table parameters in the AAL2 parameter RAM and clear the AAL2_TxWait_table
•
Set AAL2_TCT[ET] for the channels using the Timer CU mechanism
44.11 Performance Estimation
Table 44-8
represents the estimated performance of AAL2 using 100% of the CPM bandwidth. The CPM
utilization scales linearly with the data throughput. The performance numbers represent the aggregate data
rate throughput of AAL2 for both transmit and receive. Note that the performance analysis was done with
SDRAM; usage of EDO will result in a 5–10% performance reduction.
In order to evaluate the total CPM utilization of a system, the user should add the expected CPM utilization
needed for AAL2 implementation to the calculated CPM utilization using the CPM utilization tool. To
locate the utilization tool see the website at http://www.motorola.com.
For example, if a 50-MHz system is running AAL2 at 4 Mbps (aggregate) using a UTOPIA interface with
an average packet size of 20 bytes, the AAL2 channels utilize 50% of the CPM (4 Mbps out of the possible
8 Mbps). In this case, the user has 50% of the CPM bandwidth available for other purposes.
44.12 PHY Interface
AAL2 can support only T1/E1 rates per PHY line. Faster input bursts of data, such as from a 25-Mbps line,
will cause the receive buffers to overflow. AAL2 can support multiple T1/E1 connections depending on
the system’s frequency, CPM load and ATM interface; see
Section 44.11, “Performance Estimation.”
44.13 Additional Recommendations
The host application should process the AAL2_Tx_queues and AAL2_Rx_queues on an interrupt-driven
basis. Accessing the AAL2_Tx_queues and AAL2_Rx_queues using polling may result in lower AAL2
performance.
Table 44-8. Estimated AAL2 Performance
ATM
Interfac
e
System Freq
[MHz]
Average Packet
Size of 10 Bytes
Average Packet
Size of 20 Bytes
Average Packet
Size of 30 Bytes
Average Packet
Size of 40 Bytes
Serial
50
4.5 Mbps
6.5 Mbps
7 Mbps
8 Mbps
Serial
80
1
1
The 60X bus frequency is 40 MHz (half the speed of the system frequency).
4 Mbps
7 Mbps
9 Mbps
10 Mbps
UTOPIA
50
5 Mbps
8 Mbps
9 Mbps
10 Mbps
UTOPIA
80
1
4.5 Mbps
9 Mbps
12 Mbps
13 Mbps
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