Motorola MPC860 PowerQUICC User Manual page 1021

IDMA will be treated as a Ôbackground task,Õ and will only be serviced when other channels
do not require service, and will thus not interfere with them.
If IDMA is conÞgured to be a higher-priority task, then its transfers must be considered
when calculating demands on the CPM bandwidth. Table B-2 provides performance
information for the IDMA channels in their different modes. Its use is similar to the table
provided for the serial channels (Table B-1).
IDMA Memory to Memory
IDMA Mem to Mem with Burst Aligned Source/Dest Addr
IDMA Dual Address, Peripheral to Memory
IDMA Dual Address, Memory to Peripheral
IDMA Single Address, Peripheral to Memory
IDMA Single Address, Memory to Peripheral
Note:
1.Performance scales linearly with device operating frequency
2.IDMA transfer rates are independent of bus cycle length
B.3.3 Performance Calculations
Special conÞgurations veriÞed by experiment.
The performance Þgures quoted in Table B-1 can be used to estimate the overall CPM
bandwidth required in a particular system conÞguration. To calculate the total system load,
add the CPM utilization from every channel together. Assuming approximately linear
performance versus frequency, the general problem reduces to taking simple ratios:
CPM Utilization
For example, since a 25-MHz MPC860 running Ethernet (theoretically) at 22 Mbps
consumes approximately 100% of the CPM bandwidth, what bandwidth does a (practical)
10-Mbps channel require?
The above equation shows the 10-Mbps channel requiring 45% of the CPM bandwidth of
a 25 MHz MPC860.
MOTOROLA
Table B-2. IDMA Performance at 25 MHz
Protocol
serial rate
æ
= -------------------------------------
è
max serial rate
CPM Utilization = ---------------------------------- -
max serial rate
Appendix B. Serial Communications Performance
5.7 MByte/s
10.4 MByte/s
2.2 MByte/s
1.6 MByte/s
5 MByte/s
5 MByte/s
serial rate
ö æ
1
+ -------------------------------------
ø è
max serial rate
1
serial rate 10
= ----- - =
22
Appendixes
Speed
ö ¼
2
ø
2
0.45
B-5