Article

Thermal testing on reconfigurable computers

Univ. Autonoma de Madrid
IEEE Design and Test of Computers (Impact Factor: 1.62). 02/2000; 17(1):84 - 91. DOI: 10.1109/54.825679
Source: IEEE Xplore

ABSTRACT Ring-oscillators are useful to monitor the thermal status of
reconfigurable computers. No analog parts exist, and the sensors can be
dynamically inserted, moved, or eliminated

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    • "Ring oscillators (RO) are widely used as voltage controlled oscillators (VCO) in high performance integrated circuits as the fundamental block for frequency synthesizers, clock recov­ ery circuits, and clock distribution networks. The application of ring oscillators is not limited to VCOs, as ROs are used for on-chip thermal sensors [4], [5] and test structures to measure process variability [6]. The versatility of a RO is attributed to a simple CMOS implementation with no passive components, which reduces the occupied silicon area. "
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    • "This effect on temperature sensors accuracy could be mitigated at the expense of size and power consumption, when the number of inverters in a delay line is increased. Traditionally, inverter-delay temperature sensors measure temperature by timing its oscillation frequency against a reference clock and the number of oscillations is stored by a digital counter [2]. The period of oscillation is given in equation 1 and equation 2 states the frequency of oscillation. "
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    • "Several researchers have made use of ring-oscillators as compact thermal sensors on reconfigurable devices [4], [5], [6], [7], [15]. The problem of ring-oscillator frequency variation due to changes in a device's core voltage has been discussed in [6], [7], [9], [11], which also develop workarounds to the problem by applying different approaches to temperature-measurement. [7] uses a sample mode in which the application is momentarily paused in order to obtain stable measurements; [6] suggests making measurements over a range of temperatures and supply voltages, building an empirical model, then pausing the application to make measurements of the frequency and voltage, and finally plugging these values into a model that estimates temperature; in [9], experiments are conducted that show increased non-linearity of ring-oscillator frequencies at low-voltages and shows that each frequency point has a unique voltage-temperature pair; and [11] "
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    ABSTRACT: Thermal issues have resulted in growing concerns among industries fabricating various types of devices, such as Chip Multiprocessors (CMP) and reconfigurable hardware devices. Since passive cooling costs have risen considerably and packaging for worst-case is no longer practical, dynamic thermal management techniques are being devised to combat thermal effects. For such techniques to be applied effectively, it is necessary to accurately measure device temperatures at run time. Although several techniques have been proposed to measure the on-chip temperatures of reconfigurable devices, ring oscillators in many ways are a preferred choice due to their strong linear temperature-dependence and compact design using available spare reconfigurable resources. A major problem in using ring-oscillators to measure temperature, however, is their strong dependence on the core voltage of, and current distribution throughout the device under test. One of the reasons for variations in these properties is changes in the workload running on the device. Researchers have seen large shifts in the output frequencies of ring-oscillators due to core voltage swings on reconfigurable devices, and have tried to find alternate ways of measuring temperature that attempt to mitigate these effects. The need, however, is to have a workload-compensated ring oscillator-based thermometer for reconfigurable devices. To obtain this, it is first necessary to characterize the non-ideal effects of workload variations on ring oscillator response. Where non-ideal refers to impacts on ring oscillator oscillation frequency due to phenomena other than the workload's impact on device temperature. This paper performs such a characterization, in which the effects of workload variation on ring oscillator output frequency is quantified. A complete hardware-software setup is designed to collect temperature and power related data along with ring oscillator response to varying workload configurations. In addition, a potential issue with using the Xilinx System Monitor to measure die temperature at high ranges is also briefly discussed.
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