The field of the invention is that of viewing devices situated inside the flight deck of an aircraft. The invention relates to the viewing devices of which the electronic component for graphic generation or for display is sensitive to electromagnetic radiation.
An aircraft viewing device comprises a CPU/GPU (Central Processing Unit/Graphics Processing Unit) computing function more commonly called a Graphic Generation Unit. This function generates an image on the basis of input parameters carried on an external data bus which may be of the AFDX, Ethernet or CAN type for example and transmits a video stream to the display element. The display element is usually a liquid crystal (LCD) flat screen. The graphic generation function is generated by electronic components that are sensitive to electromagnetic radiation. They are usually electronic components of the FPGA (Field Programmable Gate Array) type with an SRAM (Static Random Access Memory) configuration cell. FPGAs have the advantage of allowing the implementation of complex functions and of being reprogrammable. They are volatile memory components, that is to say that their computer content is lost when they are not powered and therefore have to be initialized by a computer program each time they are started up. That is why they are accompanied by a FLASHROM (Flash Read Only Memory) memory, a nonvolatile memory, containing the program of configurations of the FPGA. When this type of component is subjected to electromagnetic radiation, it may be disrupted and this results in the loss or corruption of the image. In order to guard against this type of event, certain FPGAs incorporate a control device (CRC) which makes it possible to detect the corruption of their configuration memory. When the CRC detects such an event, the FPGA is reset in order to copy into the FPGA the computer program contained in the FLASHROM memory. This FPGA-resetting event is called an SEU (Single Event Upset). However, throughout the reconfiguration phase, the FPGA is no longer operational. The reconfiguration time lasts a few hundreds of milliseconds approximately and causes an effect that is perceptible by the user of the screen. The momentary loss of the image on a viewing device very seriously disrupts the pilot and has the effect, in most cases, of the equipment concerned being removed and replaced, even though this temporary image loss has no subsequent consequences. Paradoxically, it is possible to be in a situation in which the maintenance team carries out a replacement of the hardware when the viewing element is in perfect working order. In the case of an airline, this operation generates an unnecessary additional operating cost because of the unavailability of the airplane or because of the delay in the flight schedule.
Solutions exist that make it possible to guard against SEUs. Integrated-circuit components of ASIC (Application Specific Integrated Circuit) technology resolve this problem. They are integrated circuits etched into layers of silicon, commonly called “hardwired”. They are then insensitive to SEUs. In a network of viewing devices consisting of several graphic generation units, it would then be necessary for each graphic generation unit and display unit to be developed on an ASIC component. The development of an FPGA conversion to ASIC is actually very costly and a longer development time is involved than for an FPGA-based solution. These higher development costs arise because an ASIC solution requires the production of specific etching masks. Such a choice becomes profitable only for a sufficiently large volume. Moreover, an ASIC solution is not flexible as is the FPGA solution and therefore does not provide any possibility for the solution to be upgraded without major additional development cost.
There is an alternative that makes is possible to guard against the effect of SEUs. In the case of a modified LCD panel, the clocks of the power supply components of the lines and columns may be stopped. The liquid crystals then remain in their state thereby immobilizing the image during the electronic reconfiguration in question. The problem of this solution is that the frozen image is the last one displayed. When there is no loss of image but only corruption, the incident detection means requires a few tens of milliseconds to detect it, a sufficiently long time to display a corrupted image on the screen. This solution does not make it possible to retrieve an image prior to the detection of the incident and therefore freezes a false image. Moreover, it is necessary to modify the LCD panels. This operation causes problems in terms of mass production.
More precisely, the subject of the invention is a viewing device comprising a viewing device comprising, in succession and connected in series, a screen, a display unit and one or more graphic generation units connected to the display unit by means of a switch, the graphic generation units and the display unit having a means for detecting corruption or loss of the image, in that case initiating their reconfiguration, characterized in that the viewing device also comprises an electronic block and an associated memory, these two components recording in a loop, in nominal operation, a series of images of sufficient size so that it always comprises one valid image originating from one graphic generation unit, one valid image being an image formed before the detection of the failure by an alarm signal; when an incident is detected and is signaled to the electronic block, the electronic block transmits to the screen, for a period of reconfiguration of the electronic unit in question, the last valid image recorded in the memory.
The electronic components performing the display and graphic generation functions are usually FPGAs. During electromagnetic disturbances, they may be subject to SEUs and therefore potentially disrupt the display. The electronic block continually recording the images is insensitive to electromagnetic radiation; it is then said that the electronic component is masked. Therefore, in cases of electromagnetic radiation incidents, it is capable of presenting a valid image during the unavailability of the other graphic units; this is then called the temporary freezing of the image. An image may be considered to be unique or to be a composition of video windows. In any case, each of these entities is associated with a particular signature. The latter is transmitted to the screen by the digital video link if the window originates from an upstream case. A valid image is detected on the basis of its signature and of the incident detection means. The invention therefore consists in presenting on the screen in a temporary and controlled manner the totality or the portion concerned of the image seen by the pilot. The image series that is continuously recorded in a loop is approximately ten images. This quantity of images is sufficient to be able to retrieve an image prior to the detection of the incident. The processing time of the incident detection means is of the order of approximately ten milliseconds. The duration of freezing of the image is sufficiently short for the unique freezing effect to be tolerable and even imperceptible to the observer. Clearly, the function freezing the image on the screen is protected against the risk of a fixed image with one of the techniques known to those skilled in the art. If the problem persists, a real failure arises and the image or the relevant portion thereof is then no longer displayed.
If necessary, the hardware resource may also be used to carry out image capture. Specifically, the device optionally comprises command means that make it possible to record a displayed image in the electronic block and then transmit it to a digital output. The pilot then has a means of screen capture and of transferring the image to another screen. For example, it can specifically be envisaged that the pilot might need to show an image to another person on the flight deck. All he then has to do is to initiate a command to carry out the operation.
The invention is a solution involving less development cost in order to guard against the effects of SEUs over the whole chain generating the image. Only the additional electronic resources forming the invention are masked. In the case of multiple instrument panels, the invention prevents masking all of the display and graphic generation units. Keeping an FPGA-based and not ASIC-based configuration makes it possible to retain the advantages of flexibility and low-cost development of the FPGA architecture. Moreover, the additional elements can be positioned anywhere on the image-generation chain. The invention is suited to an architecture in which the graphic generation unit forms part of an electronic circuit board upstream of that of the display unit and to an architecture in which the graphic generation unit is integrated into the electronic circuit board of the display unit.
The invention will be better understood and other advantages will become apparent on reading the following description given in a non-limiting manner and with reference to the appended figures, among which:
As a non-limiting example, the image generation chain of
In a second embodiment according to
In a third embodiment according to
Number | Date | Country | Kind |
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07 07558 | Oct 2007 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2008/064353 | 10/23/2008 | WO | 00 | 5/28/2010 |