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Algotron: TI DSP Software For Telecoms | |
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V.42 Error Correction Software for Texas TMS320C54x/C55x DSPs This software implements the ITU Error Correction function V.42 for data transmission by full-duplex telephone modems. V.42 is an HDLC error-protection protocol termed LAPM, formulated specifically for telephone modems. Data rates can be asymmetric in each direction. The LAPM protocol first sends an initial handshake immediately after
the modem data pump handshake is concluded to determine whether the far-end
is V42-compatible. If not then transmission falls back to start-stop bit
octet formatting. On V.42 establishment, data is sent in frames of octets
with a CRC (cyclic redundancy check) remainder attached. If on reception
the computed CRC does not agree with that attached then frame re-transmission
is requested. The software is in the form of callable subroutines to handle initialisation
and to exchange data between the user interface and the modem data pump
interface of the V.42 function. Data memory is offset-addressed, so making
the code re-entrant and suitable for implementing multiple V.42 functions
per DSP. A comprehensive user's guide is supplied with the code. Test
results are available. Interfaces: at the user data interface, subroutine calls are provided so the user can both load the transmit octet buffer and empty the receive octet buffer. At the data pump interface, further subroutine calls are available to transfer data in transmit and receive directions in 16-bit blocks. To provide timer information, an additional subroutine call must be made on a regular-timed basis. At the control interface, one 16-bit control word is used to sequence operation and to report on V.42 status. DSP Load:
The MIPS figure is for 33.6kb/s full-duplex - the value scales roughly proportionate to the aggregate data rate of both directions Availability: Now - sale is under licence - integration support offered
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