Generating communication signals

摘要

A HSP Communication system (100) includes a host computer (110) which executes a software portion of an HSP modem and a device (130) containing a digital-to-analog converter (DAC) (137). In response to interrupts, the host executes an update routine that generates and writes samples to a software circular buffer (148) in memory of the host computer. The samples represent amplitudes of an analog signal complying with a desired communication protocol. A direct transfer moves samples from the software circular buffer to a hardware circular buffer (136) of the device, and the DAC converts the samples from the hardware circular buffer into an analog communication signal. In an exemplary embodiment, the hardware portion is coupled to a PCI bus in the host computer, and direct transfers are according to the PCI bus master protocol. In environments such as a multi-tasking systems, the host may skip interrupts or otherwise not provide new samples when required. In this case, the direct transfers transfer old samples, and the DAC reuses samples from the software circular buffer to generate a maintenance signal. If direct transfers are delayed, the DAC can reuse samples from the hardware circular buffer to generate the maintenance signal. The maintenance signal typically does not convey correct data but is sufficient to maintain a communication link and prevent a remote device from disconnecting or entering a retrain mode. For a better maintenance signal, the circular buffers contains samples for an integral numbers of periods of the baud frequency of the desired protocol. Error correction and retransmission can replace incorrect or lost data.