Design And Verification Of A VGA Controller

With the development of integrated circuits, digital products have gradually been found uses in every field of our lives, and there are display screens on most of the products. Therefore, there are tremendous market demands on studying the controller circuits of display screens. VGA is widely used as a standard display interface, and the display screens' controller based on VGA technique is widely used in many fields. The VGA controller is designed in this paper to control the representation of information of video and image on the display screen. With difference in design method from the past, it has the features of high portability, ease to modification. Moreover it has advantages in cutting down the design circle and reducing the production cost.The controller supports a number of color modes, including 32bpp, 24bpp, 16bpp, 8bpp grayscale, and 8bpp pseudo color. It uses WISHbone construction as bus interface, in this way it can connect with external module more efficiently ,and its working efficiency can be improved. The controller gets the image data from external video memory via the video-bank-switching technique so that the continuity of data stream can be guaranteed. In order to meet the requirements of display, the controller can change parameters of resolutions, signals polarization levels by setting the status of related registers. As is required for fulfilling our tasks, there are two color-lookup tables in it; we can increase the amount of color modes by expanding the memory of color lookup table. In this design, asynchronous FIFO is arranged to store and buffer data between two asynchronous clocks, which is important and difficult to design. Therefore, the image data can be output continuously.The emphasis of this paper is put on optimizing overall structure of VGA controller, realizing the circuit function by the easiest architecture and ensuring that each block can work in coordination based on realizing the function of each partial module. As a result, data processing can take effect in the controller.In this design, used is the top-down design methodology for ASIC to separate VGA controller into several sub-modules which are described by Verilog HDL. Tools of EDA, such as Modelsim, Synopsys DC and so on, are made use of to perform the compiling of RTL code, function verification, and design synthesis, as well as the gate level simulation. In the overall test of VGA controller, a scene test bench is made with WISHbone bus architecture being based on. It can increase the test coverage in effect and verify the various functionality of VGA controller in all its aspects. After finishing the functional verification, the logic synthesis is applied to the RTL codes. In the paper, I stress to introduce the specific process of logic synthesis and how to set up the related parameters. After optimizing, the logical circuit that is generated by DC can meet the requirements of timing.The simulation results show that the circuit designed can output color signals and timing control signals accurately and it can meet the design requirements of VGA controller.