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V.26bis Modem DSP C Code
Description:
implements the ITU Data Modem functions V.26bis & V.26, which provide
data transmission at rates of 2.4 & 1.2kb/s in half-duplex over the
telephone network and full-duplex for 4-wire leased line operation. In
both cases, an optional independently-controlled backward channel can
be incorporated for rates of up to 75b/s.
The C code is suitable for any
processor with an ANSI-compliant C compiler. It is designed especially
for efficient operation on low-cost fixed-point DSP- and general-purpose
micro-processors. All data memory is specified as 16-bit integer words.
Multiplies are integer 16x16-bit with 32-bit products.
The code is operated by one callable
subroutine for initialisation and one for main-routine processing of input/output
sample blocks and data. The user is responsible for interfacing samples
and data to hardware. The code is re-entrant to facilitate multi-channel
operation. A comprehensive user's guide is provided with the code, together
with example application files. Test results are available.
Interfaces:
at the sample interface, the code can operate at 8.0kHz and 9.6kHz sample
rates. Transmit and receive samples are transferred on a common clock,
to which the transmit clock is synchronised. The receive clock is interpolated
in the code for synchronisation to the far-end modem. At the data interface,
data is transferred in buffers under pointer control via subroutine calls.
At the control interface, the code
has one 16-bit control word to sequence operation and to set operating
parameters, and two diagnostic words to convey data transfer status and
signal quality.
Performance: over flat channels, near matched-filter performance is obtained. SNR for 10-6 Error Rate (4kHz BW noise):
- 2.4kb/s: 8.5dB Flat Channel; 11.5dB Bell 3002 Channel
- 1.2kb/s:
5.5dB Flat Channel; 8dB Bell 3002 Channel
Processor Load:
| Sample rate | MIPS# | Data memory (words) | Prog memory (bytes)# |
| 8.0kHz | 4.0(7.2) | 149(189) | 5.3k(6.5k) |
| 9.6kHz | 2.7(6.6) | 130(170) | 4.2k(5.4k) |
-
#example figures from compiling for the TI TMS320C5000(C55x) DSP processor
- figures in ( ) are with the backwards channel
Availability: NOW - sale is under licence - integration support offered
