Thread View: comp.unix.internals
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Started by Dave Humes
Tue, 15 Dec 1992 19:47
Realtime data acquisition under UNIX?
Author: Dave Humes
Date: Tue, 15 Dec 1992 19:47
Date: Tue, 15 Dec 1992 19:47
39 lines
2745 bytes
2745 bytes
We have a requirement to process analog data on an existing UNIX system in our laboratory. Continuous, gap-free acquisition is required, thus we have a realtime processing requirement. The A/D board has dual 64K X 16 bit buffers. One fills while the other is available to the host. An interrupt signals buffer full and data starts filling in the other buffer. During the interval between interrupts, the data must be moved from the A/D buffer to a disk file. The computer we are using is a Solbourne 5/602 (2 cpu Sun/SPARC) clone. It is based on a propietary bus (Kbus), but includes a 6U VME subchassis where we intend to install the A/D board. The VME bus is accessible to the host through the system I/O board which acts as a bus translator. The operating system is Solbourne's OS/MP 4.1.A3, a multiprocessing variant of the Sun operating system. The worst case occurs while processing one channel of analog data at a sample rate of 100KHz. At this rate and using an input buffer of 64K X 16 bits, an interrupt will occur every 0.66 seconds. So, every 0.66 seconds we must get 128 Kbytes of data out of the A/D, probably by doing a DMA from the input buffer to memory on the Kbus, and from there it must be appended to a file. The input buffer is mapped to VMEbus addresses. I realize that it is almost impossible to answer this question without actually trying it, but since that requires buying hardware, we'd rather not take that approach. I also realize that a number of realtime executives exist to solve this problem, but we'd rather not take that approach either if it is not strictly necessary. I would greatly appreciate hearing from anyone who has actually attempted realtime data acquisition under UNIX. Thanks. -- ------------------------------------------------------------------------------- David Humes | Johns Hopkins University Applied Physics Laboratory (410) 792-6651 | humesdg1@aplcomm.jhuapl.edu ------------------------------------------------------------------------------- -- ------------------------------------------------------------------------------- David Humes | Johns Hopkins University Applied Physics Laboratory (410) 792-6651 | humesdg1@aplcomm.jhuapl.edu
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