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V.29 Modem DSP C Code

Description: implements the data pump function of the ITU Modem Recommendation V.29, which provides full-duplex data transmission at rates of 9.6, 7.2, & 4.8kb/s over 4-wire leased lines. The software also allows half-duplex transmission over the telephone network for application with Group 3 Fax. Good error performance is assured by the use of adaptive equalisation.
         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 (Flat Channel - 4kHz BW noise):

• 9.6kb/s - 20dB; 7.2kb/s - 16dB; 4.8kb/s 12dB
  

Processor Load:

- #example figures from compiling for the TI TMS320C5000(C55x) DSP processor

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