JP2010026394A - Display controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a tearing phenomenon from occurring while suppressing the load on an MCU, in an image transfer control circuit transferring image data from the MCU to a display panel. <P>SOLUTION: For example, counter circuits 318 and 319 obtain an image input frequency (Fin) of the image data input from the MCU 10, an image output frequency (Fout) of the image data output to the display panel 20, and a one-frame image output time (T). A calculating circuit 320 calculates a Tearing generation boundary time based upon the image input frequency (Fin), image output frequency (Fout), and one-frame image output time (T). Then a generating circuit 321 generates a Tearing previous notice signal based upon the Tearing generation boundary time and gives notice to the MCU 10 to control the timing of the image data input according to the Tearing previous notice signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display control apparatus, and for example, an image transfer control circuit that transfers image data from a host processor to a display panel such as an LCD (Liquid Crystal Display) using a synchronization signal (Clock, VSYNC, etc.). (LCD Controller (LCDC)).

  In general, when image data is transferred from a host processor (for example, Micro Control Unit (MCU)) to a display panel such as an LCD, the image data from the MCU is temporarily stored in a memory in the LCDC and then output to the display panel. Is done. This compensates for the difference between the transfer rate of image data from the MCU and the transfer rate of image data requested by the display panel. However, in seamless processing such as moving image reproduction, image data input from the MCU to the LCDC and image data output from the LCDC to the display panel are performed almost simultaneously. For this reason, when the difference in transfer rate of image data cannot be compensated for, incomplete image data stored in the memory is output to the display panel, so-called tearing phenomenon of image data (tearing phenomenon) occurs. . Output of incomplete image data to the display panel causes flickering during image display.

  Conventionally, a method for suppressing the occurrence of the tearing phenomenon by thinning out image data is well known. In the case of this method, although incomplete image data can be prevented from being output to the display panel, the continuity of the image data is lost, and therefore, smooth display (flickering during image display) cannot be improved.

  On the other hand, a method for improving flicker at the time of image display accompanying the tearing phenomenon has been proposed by the following technique (for example, see Patent Document 1). That is, as a countermeasure against tearing by software processing, for example, in the MCU, a synchronization signal (VSYNC_out) issued from the LCDC to the display panel indicating whether output is in progress is monitored by an interrupt function or polling. Then, when the output of the image data from the LCDC to the display panel is confirmed by this monitoring, the input of the image data from the MCU to the LCDC is practiced at the timing when the tearing phenomenon does not occur. Thereby, the flicker at the time of the image display resulting from a tearing phenomenon can be improved.

  However, in the case of countermeasures for tearing by this software processing, there is a problem that the load on the MCU increases because the processing for confirming image data output by the MCU and the timing calculation processing for image data input are required. ing.

As described above, when the countermeasure for tearing is left to the software processing by the MCU, the occurrence of the tearing phenomenon can be prevented and the flickering at the time of image display can be improved. At the same time, there were concerns about the impact on other treatments.
JP 2001-350455 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to prevent the occurrence of tearing without imposing a heavy load on the host processor and to improve flicker at the time of image display. An object of the present invention is to provide a display control device that can perform the above-described operation.

  According to one aspect of the present invention, there is provided a display control device that converts an image signal from a host processor to a transfer rate required by the display device and transfers the image signal, and an input frequency of the image signal input from the host processor. An input frequency detection circuit that detects (Fin), an output frequency detection circuit that detects an output frequency (Fout) of the image signal output to the display device and a one-frame image output time (T), and the input frequency (Fin) ) And the output frequency (Fout) and the one-frame image output time (T), a calculation circuit for calculating a tearing occurrence boundary time for defining a time at which the occurrence of the tearing phenomenon is predicted, and A tear warning signal is generated from the tear occurrence boundary time to predict the occurrence of the tear phenomenon, and the host program A display control device comprising: a generation circuit that notifies a memory; and wherein the tear notice signal is used as a guide when the host processor controls the output timing of the image signal. The

  According to one aspect of the present invention, an image memory that stores an image signal input at a first transfer rate from a host processor, and a display device that requests the image signal stored in the image memory. A processing circuit for converting to a transfer rate of 2 and outputting; an input frequency detection circuit for detecting an input frequency (Fin) of the image signal from a synchronization signal and a clock signal input from the host processor; and the display device Output frequency detection circuit for detecting the output frequency (Fout) and 1 frame image output time (T) of the image signal, the input frequency (Fin), and the output frequency ( Fout) and a one-frame image output time (T), a tier for defining a time at which a tearing phenomenon is expected to occur And a tearing notice signal for generating a tearing notice signal for notifying the occurrence of a tearing phenomenon from the tearing occurrence boundary time and as a guide for controlling the output timing of the image signal. And a generation circuit for notifying the host processor of the display control device.

  With the above configuration, it is possible to provide a display control apparatus that can prevent the occurrence of tearing without imposing a heavy load on the host processor and can improve flickering during image display.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, it should be noted that the drawings are schematic, and the dimensions and ratios of the drawings are different from the actual ones. Moreover, it is a matter of course that the drawings include portions having different dimensional relationships and / or ratios. In particular, some embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technology of the present invention depends on the shape, structure, arrangement, etc. of components. The idea is not specified. Various changes can be made to the technical idea of the present invention without departing from the gist thereof.

[First Embodiment]
FIG. 1 shows an example of the configuration of a display control device according to the first embodiment of the present invention. Here, an image transfer control circuit (LCDC) 30 for transferring image data from the MCU 10 to the display panel (display device) 20 will be described as an example.

  As shown in FIG. 1, the image transfer control circuit 30 includes an image data input / output mechanism using a synchronization signal (such as Clock and VSYNC), an image data temporary storage mechanism, and an image data processing mechanism. The input image data acquisition circuit 311, data conversion circuit 312, memory 313, data conversion / image processing circuit 314, PLL circuit 315, synchronization signal generation circuit 316, control register 317, counter circuits 318 and 319, tearing generation boundary time Calculation circuit 320 and tearing notice signal generation circuit 321.

  Here, the MCU 10 is a host processor of the apparatus main body (for example, a mobile phone) and controls overall processing (processing) of the apparatus main body, and also transfers image data, a synchronization signal (VSYNC_in, etc.) to the display panel 20. ), A Pixel Clock signal and a control command are supplied to the image transfer control circuit 30. The MCU 10 has a function of taking a tearing notice signal from the image transfer control circuit 30 and adjusting the timing at which image data is input to the image transfer control circuit 30.

  On the other hand, the display panel 20 is constituted by an LCD or the like, and displays image data transferred from the MCU 10.

  In the image transfer control circuit 30, the input image data acquisition circuit 311 has a line memory for one to several lines, and sequentially captures image data, a synchronization signal, and a Pixel Clock signal from the MCU 10.

  The data conversion circuit 312 performs various signal processing such as gamma (γ) correction processing, image size correction (expansion / contraction) processing, color format processing, and the like on the image data input to the input image data acquisition circuit 311.

  The memory 313 is an image memory that can store image data for one frame supplied from the data conversion circuit 312.

  The data conversion / image processing circuit 314 changes the form (parallel data → serial data, image size, compression rate, format, etc.) of the image data stored in the memory 313 in accordance with the display on the display panel 20. is there.

  The PLL circuit 315 generates a high-speed clock signal necessary for outputting image data to the display panel 20.

  The synchronization signal generation circuit 316 generates a synchronization signal and a Pixel Clock signal based on the high-speed clock signal from the PLL circuit 315, and the image from the data conversion / image processing circuit 314 together with the generated synchronization signal and the Pixel Clock signal. Data is output to the display panel 20.

  The control register 317 stores a control command from the MCU 10 and sends the stored control command to the MCU 10. As control commands, various data used for setting parameters in each unit (circuit), for example, image size, line size, frequency, transfer waiting time, image input frequency (Fin) and image output frequency (Fout) ) And a prescribed value for calculating.

  The counter circuit 318 is a frequency counter (input frequency detection circuit) for acquiring an image input frequency (Fin) based on a synchronization signal (VSYNC_in) and a Pixel Clock signal from the MCU 10 given to the input image data acquisition circuit 311. It is.

  The counter circuit 319 obtains the image output frequency (Fout) and one screen transfer time (one frame image output time) T based on the synchronization signal (VSYNC_out) and the Pixel Clock signal issued to the display panel 20. A frequency counter (output frequency detection circuit).

  The calculation circuit 320 calculates the tearing generation boundary time from the outputs of the counter circuits 318 and 319, and if necessary, the clock speed and the image size (1 frame / 1 line as a reference for image data input and image data output). ), The transfer waiting time, and the like are used to determine the tearing boundary time. The tearing occurrence boundary time is information for defining the time at which the occurrence of the tearing phenomenon is predicted.

  The generation circuit 321 is, for example, a several-stage counter, and generates a tearing notice signal according to the synchronization signal (VSYNC_out) and the tearing generation boundary time from the calculation circuit 320 and notifies the MCU 10 of it.

  FIG. 2 shows an operation for generating a tearing notice signal in the image transfer control circuit 30 having the above-described configuration. In the case of the present embodiment, the tearing occurrence boundary time is calculated in the calculation circuit 320 by giving the image input frequency (Fin), the image output frequency (Fout), and the one-frame image output time (T).

  For example, as shown in FIGS. 2A to 2C, the tearing occurrence boundary time is as follows according to the range of Fout / Fin (the condition of the inclination of the image data output with respect to the condition of the inclination of the image data input). Values (a) to (c) are taken.

(A) When Fout / Fin> 2 Tearing occurrence boundary time = no solution (takes a negative value in the following formulas (2) and (3)) (1)
That is, as shown in FIG. 2A, when the inclination (y = Foutx + n) of the image data output is more than twice the inclination (y = Finx + m) of the image data input, the relationship between Fout and Fin Therefore, the tearing phenomenon always occurs (a state that is impossible for a normal system).

(B) When 2> Fout / Fin ≧ 1 Tearing occurrence boundary time = (2-Fout / Fin) T (2)
That is, as shown in FIG. 2B, when the transfer rate of the image data requested by the display panel 20 is faster than the transfer rate of the image data from the MCU 10, image data output to the display panel 20 is started. If the image data input is started between (2-Fout / Fin) T and Tearing phenomenon does not occur.

(C) When 1> Fout / Fin ≧ 0 Tearing occurrence boundary time = (1−Fout / Fin) T (3)
That is, as shown in FIG. 2C, when the transfer rate of the image data requested by the display panel 20 is slower than the transfer rate of the image data from the MCU 10, image data output to the display panel 20 is started. Then, if image data input is started after (1-Fout / Fin) T has passed, the tearing phenomenon does not occur.

  In this way, in the image transfer control circuit 30, the tearing boundary time is calculated from the above equations (2) and (3), and further, a tearing notice signal is generated based on the calculated value. Then, the generated Tearing notice signal is notified to the MCU 10. That is, in the calculation circuit 320, the occurrence of the tearing phenomenon is predicted from the image input frequency (Fin), the image output frequency (Fout), and the one-frame image output time (T) according to the above formulas (2) and (3). The tearing occurrence boundary time to be calculated is calculated. Further, the generation circuit 321 generates a tearing notice signal based on the calculated tearing boundary time and the synchronization signal (VSYNC_out). For example, when 2> Fout / Fin ≧ 1, a Tearing notice signal is generated that is at a high level only between the Tearing occurrence boundary time ((2-Fout / Fin) T) and the 1-frame image output time (T). The In addition, when 1> Fout / Fin ≧ 0, a Tearing notice signal is generated that is at a high level only between the 1 frame image output time (T) and the tearing boundary time ((1-Fout / Fin) T). The

  Thereby, the MCU 10 can easily prevent the occurrence of the tearing phenomenon by taking the tearing notice signal from the image transfer control circuit 30 as an enable signal (or interrupt signal) at the time of image output, for example. That is, the MCU 10 requires troublesome confirmation processing of image data output and timing calculation processing for image data input by controlling the timing of image data input to the image transfer control circuit 30 in accordance with the tearing notice signal. Thus, the image data can be transferred to the display panel 20 without occurrence of the tearing phenomenon.

  FIG. 3 shows the input / output timing of image data using the above Tearing notice signal. In the case of this example, for the first to third sheets of input images, for example, the timing at which image data input is started is at the low level of the Tearing notice signal, so that incomplete image data is output to the display panel 20 as an output image. It is never output.

  On the other hand, for the fourth input image, the timing for starting image data input is when the tearing notice signal is at the high level (the timing indicated by the broken line in FIG. 3). For this reason, for example, when image data input is started at a timing indicated by a broken line, a tearing phenomenon occurs, and incomplete image data is output to the display panel 20 as an output image.

  In this case, the MCU 10 changes the timing of outputting the fourth image of the input image so that the timing of starting the image data input is at the low level of the Tearing notice signal, for example, as indicated by a one-dot chain line in FIG. As a result, the third image of the input image is output again to the display panel 20 as an output image, and incomplete image data (the fourth image of the input image) is output to the display panel 20 as the output image. Can be prevented. Therefore, flicker at the time of image display can be improved, and smooth display of the image can be realized.

  In the input image and the output image, there is actually a slight transfer waiting time between the respective image data, but this is omitted in the description here.

  As described above, the output timing of the image data in the MCU 10 can be easily controlled based on the tearing notice signal from the image transfer control circuit 30 as a guide. That is, since the transfer rate of image data is uniquely determined according to the frequency, in the image transfer control circuit, the tearing phenomenon is determined from the image input frequency (Fin), the image output frequency (Fout), and the one-frame image output time (T). As a result, a tearing notice signal is notified to the MCU in advance. As a result, the MCU does not require troublesome software processing such as image data output confirmation processing and timing calculation processing for image data input, and the image data to be sent to the image transfer control circuit according to the tearing notice signal. The occurrence of the tearing phenomenon can be prevented only by changing the input timing. Therefore, it is possible not only to improve the flicker at the time of image display, but also to reduce the load on the MCU significantly compared to the conventional case where the countermeasure for tearing is left to the software processing by the MCU. The influence on other processing to be performed by the MCU can be minimized.

  In the above-described embodiment, the case where the image transfer control circuit is configured to perform the generation of the tearing notice signal has been described as an example. However, the present invention is not limited to this. For example, the image transfer control circuit is configured separately from the image transfer control circuit. The image transfer control circuit is not necessarily limited to a single chip.

  In addition, the present invention is not limited to the above (each) embodiment, and various modifications can be made without departing from the scope of the invention in the implementation stage. Further, the above (each) embodiment includes various stages of the invention, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if several constituent requirements are deleted from all the constituent requirements shown in the (each) embodiment, the problem (at least one) described in the column of the problem to be solved by the invention can be solved. When the effect (at least one of the effects) described in the “Effect” column is obtained, a configuration from which the constituent requirements are deleted can be extracted as an invention.

1 is a block diagram showing a configuration example of a display control device (image transfer control circuit) according to a first embodiment of the present invention. The figure shown in order to demonstrate the generation operation | movement of the Tearing notice signal in an image transfer control circuit. The figure which shows an example of the timing concerning the input / output of image data using the Tearing notice signal.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... MCU, 20 ... Display panel, 30 ... Image transfer control circuit, 313 ... Memory, 318, 319 ... Counter circuit, 320 ... Calculation circuit of tearing generation | occurrence | production boundary time, 321 ... Generation circuit of tearing notice signal.

Claims (5)

A display control device that converts an image signal from a host processor into a transfer rate required by the display device and transfers the image signal,
An input frequency detection circuit for detecting an input frequency (Fin) of the image signal input from the host processor;
An output frequency detection circuit for detecting an output frequency (Fout) of the image signal output to the display device and a one-frame image output time (T);
Based on the input frequency (Fin), the output frequency (Fout), and the one-frame image output time (T), a tearing occurrence boundary time for defining a time at which the occurrence of the tearing phenomenon is predicted is calculated. A calculation circuit;
Generating a tearing notice signal for notifying the occurrence of the tearing phenomenon from the tearing occurrence boundary time, and notifying the host processor;
The display control apparatus, wherein the tear notice signal is used as a guide when the host processor controls the output timing of the image signal.   The display control apparatus according to claim 1, further comprising an image memory for temporarily storing the image signal from the host processor. An image memory for storing an image signal input at a first transfer rate from the host processor;
A processing circuit that converts the image signal stored in the image memory to a second transfer rate required by the display device and outputs the second transfer rate;
An input frequency detection circuit for detecting an input frequency (Fin) of the image signal from a synchronization signal and a clock signal input from the host processor;
An output frequency detection circuit for detecting an output frequency (Fout) of the image signal and a one-frame image output time (T) from a synchronization signal and a clock signal output to the display device;
Based on the input frequency (Fin), the output frequency (Fout), and the one-frame image output time (T), a tearing occurrence boundary time for defining a time at which the occurrence of the tearing phenomenon is predicted is calculated. A calculation circuit;
Generating a tearing notice signal for notifying the occurrence of a tearing phenomenon from the tearing occurrence boundary time, and a generation circuit for notifying the host processor of the tearing notice signal as a guide when controlling the output timing of the image signal. A display control device comprising the display control device.   When the relationship between the input frequency (Fin) and the output frequency (Fout) is 2> Fout / Fin ≧ 1, the calculation circuit calculates the tearing occurrence boundary time according to the equation (2-Fout / Fin) T. The display control apparatus according to claim 1, wherein the display control apparatus calculates the display control apparatus.   When the relationship between the input frequency (Fin) and the output frequency (Fout) is 1> Fout / Fin ≧ 0, the calculating circuit calculates the tearing occurrence boundary time according to the equation (1-Fout / Fin) T. The display control apparatus according to claim 1, wherein the display control apparatus calculates the display control apparatus.

Images