Direct memory access of diffraction patterns from striated muscle--a software view.

Complete software support has been developed for a direct memory access microprocessor system used to store and analyze diffraction data from striated muscle. These studies are based on the premise that the regularly alternating light and dark regions of the fiber behave like a phase grating to incident laser light. A knowledge of the position of a diffracted order can thus be used to determine striation spacing. Since these striations are directly associated with the force generating components of the muscle, diffraction data can provide insights into the mechanism of force generation in muscle. In our system, a charge-coupled device (CCD) is used to detect diffracted order, position, and intensity. In addition, a high speed muscle puller and tension transducer are used to characterize or alter the mechanical state of the muscle. The software has been designed to allow the inexperienced user to perform sophisticated diffraction experiments. The user may present several experimental parameters: magnitude and direction of puller movement; number of frames of data to be taken; and delay of puller or scan. This has been accomplished by interleaving DMA and control loop cycles. System performance indicates that the full 256 point analog output of the CCD can be digitized and stored in about 2 ms. The data can be transferred directly from the CCD to memory leaving the CPU free for experimental control or closed-loop processing.