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V.17 Modem TMS320C5000 DSP Code

Description: implements the ITU Data Modem function V.17, which provides half-duplex data transmission at rates of 14.4, 12, 9.6, & 7.2kb/s over the telephone network for use in Group 3 Fax equipment. Good error performance is assured by the use of trellis coding and adaptive equalisation. A fast-train algorithm is implemented for resynchronisation after initial training. 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 5.3 470 3.8k
9.6kHz 5.0 450 3.5k

- #figures are for TMS320C54x operation with the assembler interface

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

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