AN2834 Freescale Semiconductor / Motorola, AN2834 Datasheet - Page 6

• Manufacturer Part Number: AN2834
• Description: AN2834, Packet Telephony Automatic Level Control on the StarCore SC140 Core
• Manufacturer: Freescale Semiconductor / Motorola

Automatic Level Control on StarCore
3
This section describes an implementation of the ALC architecture presented in Section 2 on a Freescale StarCore-
based MSC8101 DSP. Extensive real-time tests demonstrated that the ALC software implementation requires less
than 0.3 million cycles per second (MCPS), on average. A flexible application programming interface (API)
dynamically enables/disables the ALC and dynamically changes the reference signal level P
integrated into a real-time framework using the MSC8101ADS board [7] and validated for G.169 compliance using
the DSPG ECT-1 ALC tester equipment, as detailed in Section 3.2. Figure 2 shows the basic connectivity for real-
time objective testing. The ALC is integrated with an echo canceller (ECAN), and both are configured to process
TDM data provided by a T1 connection (A) and controlled via the RS-232 serial communication interface.
In additional real-time tests, the MSC8101ADS board was connected to telephones, facsimile machines, and TTY
phones via a T1 connection. No degradation was observed on DTMF detection and TTY/facsimile communication.
Subjective tests also revealed no apparent distortions.
The StarCore SC140 core is a flexible programmable DSP core that enables the emergence of computationally-
intensive communications applications by providing exceptional performance, low power consumption, efficient
compatibility, and compact code density. This core efficiently deploys a variable-length execution set (VLES)
model that achieves maximum parallelism by allowing two address generation units and four data arithmetic logic
units to execute multiple instructions in a single clock cycle.
implementation of the ALC device on the SC140 core, focusing on two important issues in the fixed-point
implementation: limited precision and computational efficiency.
6
1. For details, refer to the
cover of this document.
•
•
•
•
•
Automatic Level Control on StarCore
y
a = 1 – 2
P
N = 79
max
min
= 8096
DSPG
ECT-1
= 1 – 2
= 10
Packet Telephony Automatic Level Control on the StarCore SC140 Core, Rev. 1
–8
–(20 + 6.1824)/10
RS-232 ECAN and ALC Command Control
2
Figure 2. Connection Between MSC8101ADS and DSPG Tester
–15
–15
SC140 DSP Core Reference Manual
~ 79
2
–15
(that is, –20 dBm0)
MSC8101ADS
1
A
B
C
D
This section briefly describes the fixed-point
, which is available at the web site listed on the back
ECAN
ALC
Freescale Semiconductor
ref
. The code was