Home-made automatic embedded computer system and display card driving method thereof

[0046] The present invention will be further described in detail below in conjunction with the drawings.

[0047] A domestic independent embedded computer system and its graphics card driving method, including the Loongson 2F central processing unit, SM722 display chip, the SM722 display chip is connected to Loongson 2F through a 32-bit 33MHz/66MHz PCI bus.

[0048] To realize the Loongson 2F embedded computer system equipped with the SM722 display chip, it is necessary to completely solve the three major tasks of hardware design, firmware driver and operating system driver development. Complete the hardware design by referring to the SM722 hardware design guide and reference design released by Silicon Motion, and then use the existing pmon driver supporting SM712 (provided by Loongson Technology Co., Ltd., no detailed version number) and Linux graphics driver (Loongson Technology Co., Ltd.) The company provides, such as the kernel version number is 2.6.36, the graphics card driver version information is version 0.11.2619.21.01 July 27, 2008). Refer to the SM722 data manual to complete the hardware design, SM722 firmware layer, and kernel layer graphics driver debugging and development, which can normally guide the existing graphics operating system based on Loongson 2F (such as the winning Kylin and the co-creation desktop operating system) and display normally.

[0049] 1. Hardware design

[0050] Such as figure 1 As shown, the hardware design principle block diagram of the present invention is as follows figure 1 Shown. As shown in the figure, the home-made autonomous embedded computer system of the present invention includes a Loongson 2F central processing unit and an SM722 graphics card chip. The SM722 graphics card chip is connected to the Loongson 2F via a PCI bus. The SM722 graphics chip is connected to the display device through the VGA interface. The Loongson 2F is connected to the 1GB DDR2 memory surface mount particles through the internal integrated memory controller. The 1GB DDR2 memory consists of 8 128M memory chips. Loongson 2F also connects dual gigabit network controllers [82541(1) and 82541(1) through PCI bus, providing two LAN interfaces, LAN1 and LAN2] and South Bridge chip CS5536, and provides IDE interface and CF interface through South Bridge chip . Loongson 2F is also connected to the BOOTROM chip through the LocalIO controller, which is the system boot ROM. The SM722 graphics chip communicates with the Loongson 2F through a 32-bit 33MHz/66MHz PCI bus. They can be surface-mounted on the same circuit printed board, or on a different circuit printed board, through a PCI slot or back The board PCI cable is used for communication to realize different computer product forms; the display content is output to the display device through the VGA interface.

[0051] 2. Firmware layer driver

[0052] The firmware layer driver has image and text display and simple 2D acceleration capabilities, supports simple graphics development, log printing, and menu selection to guide the operating system and other functions;

[0053] Such as figure 2 As shown, because SM722 has a big difference in function compared to SM712, such as figure 2 According to the layout of the internal memory space of each module in the SM712 and SM722 display chips, it can be seen that the layout of the internal memory space of each module in the SM712 and SM722 display chips is completely different, and SM722 not only adds 3D graphics acceleration hardware, but also adds a lot of new Module. When driving development, it is necessary to make corresponding modifications to the above differences based on the SM712 open source driver.

[0054] In the firmware, first modify the memory space base addresses of several functional modules that need to be used in the firmware.

[0055] a. The base address of the frame buffer (FrameBuffer) of SM722 is offset by 2MB from the original 0x18000000 of SM712 and set to 0x18200000;

[0056] b. The IO register space of SM722 is changed from 0x18700000 of SM712 to 0x180C0000;

[0057] c. The drawing port register (DPR) space of SM722 is changed from the original 0x18408000 of SM712 to 0x18000000;

[0058] d. The video port register (VPR) of SM722 is changed from 0x1840C000 of SM712 to 0x18000800;

[0059] e. Adjust the memory space size from 2MB of SM712 to 8MB.

[0060] In addition, the operating clock frequency of the internal memory of the display chip needs to be adjusted within the range of 64MHz to 129MHz. The formula for calculating the MCLK clock frequency is:

[0061] MCLK=14.31818MHz×MNR÷MDR

[0062] By setting the MCLK Numerator Register (MNR) (CCR6A) value to 0x74 and the denominator register (MCLK Denominator Register, MDR) (CCRB) value to 0x14, the SM722 built-in memory frequency is set to 83.045MHz.

[0063] If you need to use 2D hardware acceleration and true color at the firmware layer, you need to implement the following functions in the graphics card driver source file sys\dev\pci\smtc2d.c source file in the pmon source directory: ①Realize the frame buffer (Framebuffer) The area copy function deCopy completes graphics movement acceleration by driving the internal memory copy operation of the graphics chip; ②Realizes the rectangular color filling function deFillRect, and completes the hardware acceleration of area filling by driving the rectangular area color filling module inside the graphics chip.

[0064] After adding the above function, in cfb_console.c [Color Framebuffer Console driver for 8/15/16/24/32bits per pixel. 8/15/16/24/32 bits per pixel color frame buffer console driver. ] Define the macro VIDEO_HW_BITBLT in the file [graphic driver supports hardware bit blt to support the hardware bit BLT graphics driver] to enable the simple acceleration function.

[0065] 3. Operating system kernel layer driver

[0066] The Linux operating system kernel layer driver supports Linux terminal display, FrameBuffer graphics development, and graphics system display based on FrameBuffer development.

[0067] In the kernel driver layer, in addition to adjusting the memory space of the SM722 graphics card internal module according to the modification method in the firmware, in order to ensure that the internal memory clock frequency of the display chip MCLK is within the specified 64MHz-129MHz range, the graphics card driver source file kernel_dir/ In drivers/staging/sm7xx/smtcfb.c, modify the blank mode of the kernel-level graphics driver. details as follows:

[0068] Enter the directory where the source code of the operating system kernel is located, use a text editor to open the graphics card driver source file [kernel_dir/drivers/staging/sm7xx/smtcfb.c] and make the following modifications:

[0069] g. Modify the base address of FrameBuffer to 0x18200000;

[0070] h. Modify the base address of the IO register space to 0x180C0000;

[0071] i. Modify the base address of the drawing port register DPR space to 0x18000000;

[0072] j. Modify the base address of the VPR space of the video port register to 0x18000800;

[0073] k. Adjust the video memory size to 8MB;

[0074] l. Set the internal memory working clock frequency MCLK of the display chip within the range of 64MHz-129MHz;

[0075] Set the MCLK Numerator Register (MNR) (CCR6A) value to 0x74 and the denominator register (MCLK Denominator Register, MDR) (CCRB) value to 0x14, thereby setting the SM722 display chip internal memory working clock frequency to 83.045 MHz. The operating clock frequency of the internal memory of the display chip set in the kernel layer of the operating system and the operating clock frequency of the internal memory of the display chip set in the firmware layer driver do not have to be the same, as long as they are within the specified range. Because the kernel has high requirements for stability, you can also set the operating clock frequency of the internal memory of the display chip to 100MHz in the firmware, and set the operating clock frequency of the internal memory of the display chip to 83.045MHz in the kernel, which is also recommended in the graphics card data manual. frequency.

[0076] The Linux kernel layer graphics card driver is a screen frame buffer (FramBuffer) driver. When other applications need to display graphics, they need to map the Framebuffer to the application space through a specific interface to perform graphics operations. In the SM722 driver, the mapping function smtc_map_smem of kernel_dir/drivers/staging/sm7xx/smtcfb.c needs to be modified. When the graphics card chip ID is 0x720 (SM722 graphics chip ID), the start address of the frame buffer sfb-> fb.fix.smem_start plus 2MB (0x200000), length) sfb-> Subtract 2MB (0x200000) from fb.fix.smem_len to ensure that other applications can obtain the correct Framebuffer base address.

[0077] After completing the above modifications, compile and install the firmware and kernel. After the product design is completed, the product can be started through the firmware and enter the debugging terminal or boot the operating system. After the operating system is started, it can enter the terminal mode or graphical interface to support the graphical development of upper-level applications and support Linux dynamic power management.