VGA

Altera Corporation 4–1 May 2006 4. SOPC Builder Components Introduction This chapter describes in detail what an SOPC Builder component is. SOPC Builder components are individual design blocks that SOPC Builder uses to integrate a larger system module. Each component consists of a structured set of files within a directory. The files in a component directory serve the following purposes: ■ Defines the hardware interface to the component, such as the names and types of I/O signals. ■ Declares any parameters that specify the structure of the component logic and the component interface. ■ Describes a configuration wizard GUI for configuring the component in SOPC Builder. ■ Provides scripts and other information SOPC Builder needs to generate the component HDL and integrate the component into the system module. ■ Contains component-related information, such as software drivers, necessary for development steps downstream from SOPC Builder. f For details on creating custom components, see the Developing SOPC Builder Components chapter in Volume 4 of the Quartus II Handbook. For details on the SOPC Builder component editor, see the Component Editor chapter in Volume 4 of the Quartus II Handbook. Sources of Components There are several sources for components, including the following: ■ The Quartus® II software, which includes SOPC Builder, installs a number of components. ■ Altera® development kits, such as the Nios® II Development Kit, provide SOPC Builder components as features. ■ Third-party developers provide SOPC Builder Ready components, including component directories and documentation on how to use the component. ■ You can package your own HDL files into a new, custom component, using the SOPC Builder component editor. 1 While it is possible to write component files manually, Altera strongly recommends you use the SOPC Builder component editor to create custom components, for reasons of consistency and forward compatibility. QII54004-6.0.0 VGA Core for Altera DE2/DE1 Boards Preliminary 1 Core Overview The VGA Core drives the signals required by the VGA digital-to-analog converter (DAC), which in turn outputs signals to a VGA-compatible monitor. The VGA Core supports both pixel and charac- ter input. It greatly simplifies the communication with the VGA DAC. Users can integrate it easily with other SOPC components through SOPC Builder. 2 Functional Description TheVGACore generates the timing signals required for VGAdisplay, including horizontal and verti- cal synchronization signals. The timing information generated by the VGA Core produces a screen resolution of 640×480 pixels at a refresh rate of 60 frames per second. To generate the timing in- formation correctly, a 25 MHz clock needs to be provided to the VGA Core. This clock is referred to as the VGA internal clock. In addition, another 25 MHz clock signal, with 180 degree phase shift to the VGA internal clock, needs to be connected to the VGA DAC on the DE2/DE1 Boards via the VGA_CLK pin on the boards. The VGA Core runs at 25 MHz; the slave ports to the VGA Core runs at 50 MHz. Though the VGA Core only generates images at a resolution of 640×480 pixels, smaller resolutions are supported. To achieve these smaller resolutions, the VGA Core replicates pixel information to adjacent pixels to achieve the actual screen resolution of 640×480. The VGA Core supports a character mode in addition to the pixel mode. Figure 1 shows a block diagram of the VGA Core (For details of the DAC, refer to Video DAC Datasheet). The VGA Core uses the SRAM chip on the DE2/DE1 as a pixel frame buffer and uses on-chip memory as a character buffer. The following sections describe the different modes of the VGA Core. 2.1 VGA Display Modes TheVGACore can support three displaymodes: pixelmode, charactermode, and character overlay mode. The pixel and character modes have their own Avalon slave interfaces, avalon_pixel_slave and avalon_character_slave, respectively. These slave interfaces present twoflat, contiguousmem- ory spaces as large as is needed to hold the data required by the chosen resolutions. Therefore, the Avalon interfaces behave as simplememory interfaces, except when back buffering is enabled (See Sec 2.2.3 for details). There are no memory-mapped control registers on either of the Avalon in- terfaces. In the character overlay mode, both pixel and character modes are enabled such that characters are drawn on top of the pixel mode’s image. Altera Corporation - University Program October 2006 1 VGA CORE FOR ALTERA DE2/DE1 BOARDS Preliminary Reset Clock Pixel Buffer DAC Module VGA Controller Avalon Swtich Fabric Signals To VGA To SRAM Character Buffer (On-Chip Memory) Pixel Clock Monitor Figure 1. Block diagram for VGA Core 2.2 Pixel Mode In pixel mode, the user can provide the color of each pixel to the Avalon Interface, avalon_pixel_slave, of the VGA Core. The VGA Core uses the SRAM chip on the DE2/DE1 boards as the pixel buffer. This mode is suitable for animation or image display on a VGA monitor. In pixel mode, color and resolution of the VGA Core can be configured in the following ways. 2.2.1 Color Setting In pixel mode, the VGA Core uses the RGB color model. The following color space settings are available: • 16-bit color mode. Red and blue have 5-bit color spaces. Green has a 6-bit color space. • 8-bit color mode for grayscale. 2.2.2 Resolution The VGA Core supports 640× 480 resolution, which means there are 640× 480 = 307,200 pixels. However, due to the size limitation of the frame buffer, a lower resolution may be needed. To support lower resolutions, the VGA Core uses mega-pixels, where a mega-pixel is just a group of pixels that have the same color, to reduce the output resolution. The following “resolutions” on the mega-pixel level are available: • 640×480. Each mega-pixel is just a pixel. • 320×240. Each mega-pixel is a 2×2 pixel group. • 160×120. Each mega-pixel is a 4×4 pixel group. • 80×60. Each mega-pixel is an 8×8 pixel group. • 40×30. Each mega-pixel is a 16×16 pixel group. 2 Altera Corporation - University Program October 2006 VGA CORE FOR ALTERA DE2/DE1 BOARDS Preliminary 2.2.3 Back Buffer Back buffering is a technique used to reduce or remove visible artifacts from the drawing process. Two image buffers are used and, at any one time, a frame in one buffer is actively displayed by the VGA monitor, while a frame in another buffer is drawn. When drawing is completed, the roles of the two frames are switched, so that the previously shown frame is modified, and the previously drawn frame is shown. In pixel mode, bit b31 of the data is used to change the frame buffer. The user should set b31 of the last pixel in a frame to 1 so that the VGA Core switches the frame in the background buffer and the frame that is displayed to the screen. Note that switching the back buffer takes time because the VGA Core must wait until the displayed frame has been completely drawn, which can take up to 1 60 second. The user can read the highest memory location of the avalon_pixel_slave to check if the frame buffers have been switched. If the least significant bit (LSB) is 1, the image buffers are still in the process of being switched. Pixels cannot be read or written while the buffers are being switched, and trying to do so results in undefined behavior. 2.3 Character Mode In character mode, the unit of operation is characters. A device can send ASCII character codes to the VGA Core’s Avalon interface avalon_char_slave. The VGA Core handles the conversion of characters to pixels. Upon initialization or reset, the VGA core sets all the characters to “space”, so no characters will get displayed. This “clear screen” operation can take up to 5000 clock cycles to finish, which, in general, will not cause any problems. After initialization, the user can clear the screen by writing 1 to the highest memory location of the avalon_char_slave. The VGA core sets the LSB of the word to 1 if it is in the process of clearing, or to 0 if the clear screen operation is done. During the clearing process, no data can be read or written to the character slave, and trying to do so results in undefined behavior. 2.3.1 Color Setting In character mode, the VGA Core also uses the RGB color model, but fewer color space settings are supported than are supported in pixel mode: • 9-bit color mode. Each color (red, green, and blue) has a 3-bit color space. • 8-bit color mode. This mode stores colors in a look-up table in the VGA Core and uses the 8 bits as an index to the look-up table. Four bits are for the foreground color and four bits are for the background color. Also, another bit is used to indicate whether the background color is transparent. • 4-bit color mode. This mode stores colors in a look-up table in the VGA Core and uses the 4 bits as an index to the look-up table. • 1-bit color mode. Characters are drawn in white with transparent background. Altera Corporation - University Program October 2006 3 VGA CORE FOR ALTERA DE2/DE1 BOARDS Preliminary 2.3.2 Resolution/Character Size In character mode, the resolution is defined by the number of characters per line and the number of lines per screen. All the characters have to be the same size. Two sizes are supported: • 8× 8. Each character occupies an 8× 8 VGA pixel group. Therefore, 80 characters can be displayed per line and the VGA Core can support up to 60 lines. • 16×16. Each character occupies a 16×16 VGA pixel group. Therefore, 40 characters can be displayed per line and the VGA Core can support up to 30 lines. 2.4 Character Overlay Mode In character overlay mode, both characters and pixels get displayed, with the character layer on top of the pixel layer. The background of characters are transparent, except in 8-bit color mode, where the transparency is optional on a per-character basis. 2.5 Address Format Coordinates are memory-mapped in the VGA Core’s addressable space. All data for the VGA Core is word (32-bit) addressable. The supported addressing mode is called the X-Y mode. • X-Y mode — the address contains x and y coordinates. The coordinate system is shown in Figure 2. x y 0 1 2 3 4 1 2 3 .... ... . 0 1 2 3 4 0 Figure 2. Video coordinate system The format of the address is shown in Figure 3. 31 01 00X coordinate (m bits)Y coordinate (n bits)Not used Figure 3. X-Y address format The values ofm and n are related to the VGA Core’s resolution as follows: m = cei l (log2X ) n = cei l (log2Y ) 4 Altera Corporation - University Program October 2006 VGA CORE FOR ALTERA DE2/DE1 BOARDS Preliminary where X and Y are the resolution in the X, Y direction, respectively. For example, for 80×60 resolution we have cei l (log280)= 7 cei l (log260)= 6 So for this resolution the address format is shown in Figure 4. 31 01 00 28 X coordinate 914 Y coordinate 15 Not used Figure 4. X-Y address format for 80×60 resolution 2.6 Data Format 2.6.1 Pixel Slave’s Data Format • 16-bit color mode — Red and blue have 5-bit color space; green has 6-bit color space. The data format is shown in Figure 5. 31 04 B 510 G 1115 R 16 Not used Figure 5. Pixel slave’s data format for 16-bit color mode • 8-bit color mode for gray scale — the data format is shown in Figure 6. 31 07 Grayscale 8 Not used Figure 6. Pixel slave’s data format for 8-bit color mode Altera Corporation - University Program October 2006 5 VGA CORE FOR ALTERA DE2/DE1 BOARDS Preliminary 2.6.2 Character Slave’s Data Format Below shows the data format for the character slave under different modes. • 9-bit color mode — The data format is shown in Figure 7. The R, G, B values specify the foreground color of a character. 31 06 ASCII 7 0 810 B 1113 G 1416 R 17 Not used Figure 7. Character slave’s data format for 9-bit color mode • 8-bit color mode — The data format is shown in Figure 8. The T field indicates the trans- parency of the background color, with T = 0 for non-transparent background color and T = 1 for transparent background color. The FG and BG fields are foreground and background color indexes, respectively. 31 06 ASCII 7 0 811 FG 1215 BG 16 T 17 Not used Figure 8. Character slave’s data format for 8-bit color mode • 4-bit color mode — The data format is shown in Figure 9. The FG field is foreground color index. 31 06 ASCII 7 0 811 FG 12 Not used Figure 9. Character slave’s data format for 4-bit color mode • 1-bit color mode— the character color is white and the background is transparent. The data format is shown in Figure 10. There is no bit in the data format used for color, since pixels are either white, if the pixel is part of the character being displayed, or transparent, if the pixel is not part of the character. 31 06 ASCII 7 Not used Figure 10. Character slave’s data format for 1-bit color mode 6 Altera Corporation - University Program October 2006 VGA CORE FOR ALTERA DE2/DE1 BOARDS Preliminary 3 Instantiating the Core in SOPC Builder Designers use the VGA Core’s configuration wizard in the SOPC Builder to specify the desired fea- tures. The following sections describe the available options in the configuration wizard. 3.1 Mode Tab The options in this tab control the operating modes of the VGA Core. The following options are available: Pixel Mode —Enables the pixel mode, which is explained in Section 2.2. Character Mode —Enable the character mode, which is explained in Section 2.3. Character OverlayMode —Enable the character overlay mode, which is explained in 2.4. 3.2 Pixel Mode Setting Options in this tab control the resolution and color setting of the VGA Core, as well as the use of the back buffer. 3.3 Character Mode Setting Options in this tab control the character size and color setting of the VGA Core. 3.4 Clock Setting After the VGA Core is instantiated in the SOPC Builder, it requires three clock signals to be con- nected as follows: • VGA — 25 MHz. This clock signal is used inside the Core and has a 180 degree phase shift with the VGA_CLK signal that outputs to the VGA DAC. • avalon_pixel_slave Port — 50MHz. • avalon_character_slave Port — 50MHz. Another Altera University Program IP Core named Development Board External Interface can cre- ate the necessary signals automatically. Refer to that component’s documentation on how to prop- erly instantiate and connect it to a system. 4 Software Programming Model 4.1 Programming with the VGA Core The VGA Core is packaged with C-language functions accessible through the SOPC Builder- generated software development kit (SDK) libraries. These functions implement basic operations that users need for the VGA Core. When using the Altera Debug Client, these functions are auto- matically provided for use in a C-language application program. They are presented in Section 4.2. To use the functions, the C code must include the statement: #include "alt_up_vga.h" Altera Corporation - University Program October 2006 7 VGA CORE FOR ALTERA DE2/DE1 BOARDS Preliminary 4.2 VGA Functions 4.2.1 int alt up vga draw pixel (alt u32 pixel, unsigned x, unsigned y) Draw a pixel in the location specified by (x, y) on the VGAmonitor. Parameters: pixel – the pixel x – the x coordinate y – the y coordinate Returns: 0 for success, -1 for error (such as out of bounds) 4.2.2 int alt up vga draw char (alt u8 ch, unsigned x, unsigned y) Draw a character to the location specified by (x, y) on the VGAmonitor. Parameters: ch – the character to draw x – the x coordinate y – the y coordinate Returns: 0 for success, -1 for error (such as out of bounds) 5 RGB Color Table Table 1 shows the RGB composition of some commonly-used colors. Please note that RGB values here have a range of 0 to 255. While using the VGA Core, users may need to adjust the value range according to different modes. Table 1. RGB Color Table Color Name R G B Color Red 255 0 0 Green 0 255 0 Blue 0 0 255 Yellow 255 255 0 Cyan 0 255 255 Magenta 255 0 255 ■ 8 Altera Corporation - University Program October 2006 1 Core Overview 2 Functional Description 2.1 VGA Display Modes 2.2 Pixel Mode 2.2.1 Color Setting 2.2.2 Resolution 2.2.3 Back Buffer 2.3 Character Mode 2.3.1 Color Setting 2.3.2 Resolution/Character Size 2.4 Character Overlay Mode 2.5 Address Format 2.6 Data Format 2.6.1 Pixel Slave's Data Format 2.6.2 Character Slave's Data Format 3 Instantiating the Core in SOPC Builder 3.1 Mode Tab 3.2 Pixel Mode Setting 3.3 Character Mode Setting 3.4 Clock Setting 4 Software Programming Model 4.1 Programming with the VGA Core 4.2 VGA Functions 4.2.1 alt_up_vga_draw_pixel 4.2.2 alt_up_vga_draw_char 5 RGB Color Table