V Series Modem Interface
for TMS320C3x/'C4x
by DSP Software Engineering, Inc.

Software Overview

The V Series Modem Interface (VMI)  is a standard software front-end to all DSPSE modem products. 
VMI simplifies the task of integrating multiple modem standards by providing a single entry and 
exit point to all modem functions. VMI also contains a number of complex data-conversion, 
data-framing, and modem-interconnect algorithms. Included are: simple data packing , 
asynchronous-to-synchronous conversions, HDLC link-layer protocols, and DTE-to-DCE circuit 
emulation.  
VMI is a software layer that vectors generic modem I/O requests to a specific V-series transmitter 
and/or receiver. Input data is processed through an elastic buffer to smooth out bursts and provide 
a continuous transmit stream.

Features and Benefits

•	User-configurable HDLC protocol framing and reception
•	Provides a simple and consistent byte-oriented, frame-based interface
•	V.24 DTE-to-DCE circuit emulation
•	User-selectable processing frame size and decoding rate
•	V.14 asynchronous-to-synchronous conversion with speed matching and break detect/generation
•	Object-based interface
•	User-configurable elastic input buffer
•	Independent C-callable functions
•	Allows fast upgrade to next-generation DSPSE modems
•	SPOX compatible

Processor and System Requirements

•	Devices supported: TMS320C3x, TMS320C4x
•	Algorithm category: Modem
•	Requirements:
All memory requirements are in units of 32-bit words. The MIPs ratings presented require the listed 
amounts of on-chip, zero-wait-state program and data memory. Processor loading based on baud rate 
of modem referenced by VMI. Values shown are based on a V.32 bis modem running at 14,400 bits per 
second. Lower-speed modems require fewer MIPS. All measurements were made using an executable 
demonstration built for a third-party PC plug-in board.
Function
Avg MIPS
Chip RAM
Data
Program
Transmit/Receive
1.8
0.2 k
0.3 k
4 k

User Functions

The VMI software package consists of several independent, C-callable functions that perform the 
full-duplex modem function as well as status, control, and messaging operations. It also includes 
functions that reflect the implementation's object-based interface. The encoder and decoder 
interface with linear arrays of 16-bit linear PCM samples and 8-bit characters.
V Series Modem Interface
VMI_create (...)
Dynamically allocates and initializes data memory for encoder
VMI_delete (...)
Frees encoder's usage of dynamically-allocated data memory
VMI_process (...)
Full-duplex modem function
VMI_status(...)
Return status of the modem
VMI_control(...)
Set operating parameters of the modem
VMI_message(...)
Send messages to the modem

Algorithm Verification

•	Call DSPSE for verification details

Availability

•	Source and object code currently available for licensing.

Company Background and Contact Information

DSP Software Engineering, Inc. is a leading provider of highly-complex digital-signal-processing 
software used in telecom-munications and multimedia applications.

Contact:	DSP Software Engineering, Inc.
		175 Middlesex Turnpike
		Bedford, MA 01730  USA
		(617) 275-3733
		Fax: (617) 275-4323
		e-mail:  info@dspse.com
		www:  http://www.dspnet.com