Soft Modems use the main processor to execute modem functions traditionally performed by the hardware on the modem card. We analyzed and studied the vendor version of a driver for a popular soft modem that executes its signal processing work in interrupt context. We created three modified versions of the driver that execute the signal processing routines in the context of a DPC, a thread scheduled under the NT scheduler, and a thread scheduled using the real-time Rialto/NT scheduler, respectively. We captured performance profiles of each of the four versions of the driver and compared and contrasted the modem performance. We conclude that (1) signal processing in interrupt context is not only unnecessary but also detrimental to the predictability of other computations in the system and (2) a real-time scheduler can provide predictability for the soft modem while minimizing the impact of the modem on other computations in the system.
