Translator Disclaimer
Paper
10 July 2008 Fixed-point vs. floating-point arithmetic comparison for adaptive optics real-time control computation
Author Affiliations +
Abstract
Most computers in the past have been equipped with floating point processing capabilities, allowing an easy and brute-force solution for the machine computation errors, not requiring any specific tailoring of the computation in nearly hundred percent of situations. However, the computation needed for the adaptive optics real-time control in 30-50 meter telescopes is big enough to cause trouble to conventional von-Neumann processors, even if Moore's Law is valid for the next years. Field Programmable Gate Array (FPGAs) have been proposed as a viable alternative to cope with such computation needs[1,2], but--at least today's chips--will require fixed-point arithmetic to be used instead. It is then important to evaluate up to what point the accuracy and stability of the control system will be affected by this limitation. This paper presents the simulation and laboratory results of the comparison between both arithmetics, specifically evaluated in an adaptive optics system. The real-time controller has been modeled as black box having as input the wavefront sensor camera digital output data, providing a digital output to the actuators of the deformable mirror, and with the task of internally computing all outputs from the inputs. MATLAB fixed-point library has been used to evaluate the effect of different precision lengths (5-10 fractional bits) in the computation of the Shack-Hartmann subaperture centroid, in comparison with the reference 64-bit floating-point arithmetic and with the noise floor of the real system, concluding that the effect of the limited precision can be overcome by adequately selecting the number of fractional bits used in the representation, and tailoring that number with the needs at every step of the algorithm.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Yolanda Martín-Hernando, Luis Fernando Rodríguez-Ramos, and Marcos Reyes Garcia-Talavera "Fixed-point vs. floating-point arithmetic comparison for adaptive optics real-time control computation", Proc. SPIE 7015, Adaptive Optics Systems, 70152Z (10 July 2008); https://doi.org/10.1117/12.787408
PROCEEDINGS
12 PAGES


SHARE
Advertisement
Advertisement
RELATED CONTENT

FPGA-accelerated adaptive optics wavefront control
Proceedings of SPIE (March 07 2014)
The woofer-tweeter experiment
Proceedings of SPIE (June 28 2006)
FPGA adaptive optics system test bench
Proceedings of SPIE (August 25 2005)
Control laws for a multiconjugate adaptive optics system
Proceedings of SPIE (October 25 2004)
FPGA based real time controller for high order correction in...
Proceedings of SPIE (September 13 2012)

Back to Top