AlgoTron DSP
Software for Telecoms & Audio
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V.25 Modem Function TMS320C5000 DSP Code
Description:
implements the ITU function V.25 for data modems. This is the 2100Hz auto-answer
sequence sent from the answering end at the start of a PSTN modem connection.
As well as audibly denoting a far-end modem in answer mode, the 2100Hz
signal automatically disables network echo suppressors and, if periodically
phase reversed as with the code here, also network echo cancellers.
The supplied V.25 code is intended to be used
as an adjunct to a V- (or Bell-) series modem data pump function. Segment
timings of the initial zero signal and the 2100Hz tone can be re-programmed.
Note that some Algotron data pumps such as V.22(bis) and V.32(bis) can
for convenience implement the V.25 sequence as part of the data pump handshake,
so do not require this additional code module unless for its programmability.
The assembler software is operated
by callable subroutines, eg for initialisation and for per-sample processing
of input/output samples. The user is responsible for interfacing samples
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.
Interfaces: at the sample interface, the code can operate at 8.0kHz and 9.6kHz sample rates. At the control interface, the assembler code has control word access to set V.25 segment durations, to sequence operation and to set operating parameters such as data size, and one diagnostic word to convey data transfer status such as V.25 progress. With the C wrapper, control and diagnostics are provided by routine call arguments and returned values.
Processor Load:
| Sample rate | MIPS# | Data memory (words) | Prog memory (bytes)# |
| 8.0kHz | 1.7 | 52 | 0.3k |
| 9.6kHz | 2.0 |
- #figures are for TMS320C54x operation with the assembler interface
Availability: NOW - sale is under licence - integration support offered
