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V.33 Modem TMS320C5000 DSP Code

Description: implements the ITU Data Modem function V.33, which provides full-duplex data transmission at rates of 14.4 & 12kb/s over 4-wire leased lines. The software also allows half-duplex transmission over the telephone network. Good error performance is assured by the use of trellis coding and adaptive equalisation. The assembler software is in the form of callable subroutines, eg for initialisation and for main-routine processing of input/output sample blocks and data. The user is responsible for interfacing samples and data to hardware.
         In the assembler interface, the code is re-entrant to facilitate multi-channel operation. A C-callable wrapper can also be provided, allowing individual channels to be called from C to process multiple sample blocks. A comprehensive user's guide together with example application files are provided with the code. 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 DSP code for synchronisation to the far-end modem. At the data interface, data is transferred in buffers under pointer control.
         At the control interface, the assembler 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. With the C wrapper, control and diagnostics are provided by routine call arguments and returned values.

Performance: sophisticated techniques have been incorporated into the software to give excellent performance under noisy or poor line conditions. Over flat channels, near matched-filter performance is obtained. Over very severe channels such as the TAS Telephone Network Emulator ConUS Poor Voice channel – 30dB attenuation across the 3kHz band – the modem code will still operate at 14.4kb/s. SNR for 10-6 Error Rate at 14.4kb/s (4kHz BW noise):

  • 22dB Flat Channel ; 26dB Bell 3002 Channel

Processor Load:

Sample rate MIPS# Data memory (words) Prog memory (bytes)#
8.0kHz 5.4 470 3.8k
9.6kHz 5.1 450 3.6k

- #figures are for TMS320C54x operation with the assembler interface

Availability: NOW - sale is under licence - integration support offered

 
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