AN2333 Freescale Semiconductor / Motorola, AN2333 Datasheet - Page 14

• Manufacturer Part Number: AN2333
• Description: Maximizing the Performance of Two Fast Ethernet Links on MSC8101 FCCs
• Manufacturer: Freescale Semiconductor / Motorola

Results and Conclusions
3.6 Timer and Statistics
4
14
Results and Conclusions
In its default configuration, the 2FCC project works with a reduced context switching ISR in conjunction
with an ASM FCC interrupt handler. However, the timer interrupt handler is not written in ASM and can
potentially use registers that are not yet saved when a timer interrupt occurs. In most systems, this would
lead to crashes, but in the 2FCC project, the main program is an empty infinite loop that executes no
instructions. Thus, the fact that the timer interrupt handler is not written in ASM has no impact.
The direct application of the 2FCCs project is the benchmarking for Voice over IP (VoIP) systems. The
array shown in Table 5 gives the Ethernet frame size for VoIP/G711 communications. The test runs the
project for different frame sizes, from 64 to 1500 bytes with several steps including the values shown.
The hardware and software assumptions for this test are described in the previous sections of this
document.
The validity of the test is limited. In fact, the use of a software tool called CPM_Perf (see Section 5),
indicates that the CPM RISC processor does not run under normal conditions (saturation) when the frame
size is less than approximately 138 bytes. The maximum MSC8101 speed configuration is SC140
core/CPM/system bus = 300/150/100 MHz, and the minimum frame size is approximately 64 bytes. See
the calculations for these two scenarios in the results matrix of the 2FCCs test (Table 7).
The throughput divergence between the FCCs is a confirmation of the expected limit (138 bytes) given by
the CPM_Perf tool. At full speed, this limitation disappears. Sometimes the debugger I/O window
displayed the message discarded frames = 2 because of BD resynchronization after the timer
G711 X (Ms)
Frequency (Hz)
Voice payload (bytes)
RTP (bytes)
UDP (bytes)
IP (bytes)
Ethernet MAC @ (bytes)
Ethernet CRC (bytes)
Total size of a packet (bytes)
Throughput for one full duplex (Tx and Rx)
channel (kbits/s)
G711 X (Ms)
Ethernet frame length
FCC1 throughput (Mbits/s)
FCC2 throughput (Mbits/s)
Total throughput (Mbits/s)
Interrupt frequency (1/s)
Number of channels
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1803125
Table 6. 2FFCs Throughput Performances
115.4
54.9
60.5
64
Table 5. G711 Figures for Frame Size
X
X
1612821
125.8
65.4
60.4
504
2.5
78
1593878
156.2
249.6
77.8
78.4
996
400
98
2.5
20
12
20
14
78
5
8
4
1217391
1522
138
168
10
84
84
156.8
200
40
12
20
14
98
5
8
4
819266
178.6
2048
89.3
89.3
218
20
379200
189.6
110.4
94.8
94.8
500
100
138
10
80
12
20
14
X
X
8
4
193600
193.6
1000
96.8
96.8
X
X
87.2
160
218
20
50
12
20
14
8
4
129600
194.4
1500
97.2
97.2
X
X