Application of PowerPC in Vehicle Display and Control System

The vehicle display and control system is a system that displays and controls the vehicle's working status information and completes human-computer interaction. The vehicle display and control system needs to respond to key operations while displaying text, graphics and videos, and control the vehicle control system. This requires the system to have the ability to respond in real time and process multiple tasks in parallel. This paper applies the real-time operating system VxWorks on the control motherboard with PowerPC MPC8548E as the processor, and realizes the function of real-time response to system operations and display of corresponding information. The display and control system with this motherboard as the core control motherboard has high performance, high stability and good compatibility.

1 Overview of PowerPC MPC8548 and its control motherboard

PowerPC MPC8548 is a high-performance processor of the new generation PowerQUICC III series developed by Freescale. Its internal operating frequency can reach 1.33 GHz, and its processing performance can reach 3 065MIPS at this operating frequency. The first-level cache has 32 KB of instruction cache and data cache, and the second-level cache is 512 KB. It supports DDR1 and DDR2 memory controllers, PCI, PCI-X and PCIE interfaces, SRapid IO interface and 4 GbE interfaces. MPC8548 not only has powerful data processing capabilities, but also has strong communication processing capabilities, high reliability, and good resistance to harsh environments. It is particularly suitable for occasions with high requirements for network performance and multiple interfaces.

The core control motherboard of the vehicle display and control system is an embedded system with PowerPCMPC8548E as the processor. The system forms a high-performance and high-reliability core control motherboard by expanding the display, memory, Flash memory and other interface control circuits. With this control motherboard as the hardware platform, the embedded real-time operating system VxWorks is transplanted, the interface device driver is secondary developed, and then VxWorks is used as the software development platform to develop applications to achieve display and control tasks.

2 PowerPC control motherboard hardware design

As shown in Figure 1, the hardware system of the PowerPC control motherboard consists of a processor, peripheral circuits, and external interface devices. The peripheral circuits include power supply, crystal oscillator, and reset circuits; the external interface circuits include serial ports, network ports, EL/LVDS LCD, 16-bit PCI bus, USB port, Flash, mouse, and keyboard, etc.

3 PowerPC control motherboard software design

The vehicle display and control system is a complex real-time embedded system with multiple tasks. It uses an operating system to allocate, schedule, control and coordinate all software and hardware resources, especially to coordinate concurrent activities, such as task scheduling, memory management, synchronization mechanism, exception and interrupt handling, and inter-task communication. VxWorks of WindRiver (now acquired by Intel) is a real-time embedded operating system. The VxWorks operating system has been widely used in aviation, automobile and other industries. Given VxWorks' support for the PowerPC processor architecture, most embedded systems using PowerPC processors use it as the operating system. Therefore, the vehicle display and control system also uses VxWorks as the operating system.

An embedded system is a system that configures and cuts hardware resources according to actual requirements. Since embedded products are a combination of hardware and software, and as the product is developed, the software has been solidified in the hardware environment, therefore, the integrated development of hardware and software is a major feature of embedded systems, and software design is completed on the basis of close connection with hardware.

The software design of the PowerPC control motherboard follows the architectural design method of embedded software and is divided into the following two parts:

① Development of special device drivers and integration of general device drivers, that is, development of board support package BSP.

② Development of application programs, that is, the implementation of display and control tasks.

3.1 Device driver development

Since the hardware platform of this system is designed according to actual needs, the device driver must be developed according to the actual interface. Based on the architecture of the general device driver provided by VxWorks, combined with the working principle and function of each specific device, with data flow as the center, after mastering the communication method between the device and the CPU and external devices, the driver of the specific device is developed one by one. After the device driver is developed, the board support package BSP of MPC8548E is finally formed. The integration of hardware device programs includes the following aspects.

(1) Special device drivers

The drivers for some special devices are not included in the standard device list of VxWorks, so they need to be developed by yourself, such as PCI line drivers, DDR memory drivers, and display drivers.

(2) General device driver

The drivers of common devices can directly apply VxWorks standard drivers, or make slight modifications based on standard drivers, such as mouse, keyboard, serial port, Ethernet interface and USB interface.

3.2 Application Development

First, the tasks to be completed by the vehicle display and control system are decomposed into multiple tasks: key query, interface switching, data display, video display and parameter storage. The application ensures that each task is completed in real time in a prescribed manner. The software structure diagram of the PowerPC control motherboard is shown in Figure 2.

Key query: Periodically query whether a key is pressed. If so, send messages to interface switching, data display, video display and parameter storage to complete the corresponding tasks.

Interface switching: switch to the corresponding interface.

Data display: Displays the status of the vehicle control system in different working modes.

Video display: switch video channels, adjust image brightness and contrast, and perform related operations.

Parameter storage: Save parameters according to instructions, or save parameters to cache at equal intervals.

3.2.1 Software Implementation of I2C Interface Control

The I2C bus is a two-wire serial bus that is mainly used for the expansion of microprocessor peripheral chips. It only needs two wires, a serial data line and a serial clock line, to realize data exchange between the microprocessor and the device with an I2C bus interface on the bus.

I2C bus devices are widely used for their simplicity and effectiveness. One of them is the video decoder CCX25836 used for analog video display in the vehicle display and control system. The registers of CCX25836 need to be configured using the I2C bus. The system design uses FPGA to build the hardware I2C electrical structure. On the PowerPC control motherboard, the software is used to simulate the I2C read and write process required by the video decoder to set its registers, thereby realizing video display functions such as switching of video channels, adjustment of brightness and contrast. The I2C read and write process is shown in Figures 3 and 4, and the process of setting brightness and contrast through the I2C bus is shown in Figure 5.

3.2.2 Communication between devices via PCI local bus

The PCI local bus is the interconnection interface between the processor/memory and the peripheral control components and expansion cards in a microcomputer. The PCI local bus specification is the protocol of the interconnection mechanism and the specification of the electrical and mechanical configuration. The PCI local bus has bus master support and automatic configuration functions, and provides three types of address space, namely memory, I/O and configuration address space. These features lay the foundation for communication between devices on the bus.

There are multiple PCI devices in the vehicle display and control system. In view of the strong processing power of PowerPC and the real-time multitasking function of the real-time operating system, the PowerPC control motherboard becomes the "master device" responsible for coordination between devices, and other devices are "slave devices". The "master device" configures the "slave device" according to its device identification number and vendor identification number, and performs data communication according to the storage mapping access method of the address space. The communication process between PCI devices is shown in Figure 6.

3.3 Connection between application program and device driver

Applications access devices by calling device drivers. There are three ways to call device drivers: direct calling, calling through the operating system kernel, and calling through the operating system extension module. Direct calling allows applications to access devices efficiently, but has poor portability and users need to manage the devices themselves; calling through the kernel is managed by the operating system and has good portability, but increases system overhead; the advantages and disadvantages of calling through the extension module are similar to those of calling through the kernel.

The vehicle display and control system is a complex real-time operating system that requires good portability and has extension modules. Therefore, the application uses both the kernel and extension modules to call the device driver. The kernel calls the general device driver, and the extension module calls the special driver.

3.4 Direct connection between application and device

In response to the control requirements of some special devices, the PowerPC control motherboard adopts direct control instead of device drivers.

The I2C bus is a two-wire serial bus that is mainly used for the expansion of microprocessor peripheral chips. It only needs two wires, a serial data line and a serial clock line, to realize data exchange between the microprocessor and the device with an I2C bus interface on the bus.

I2C bus devices are widely used for their simplicity and effectiveness. One of them is the video decoder CCX25836 used for analog video display in the vehicle display and control system. The registers of CCX25836 need to be configured using the I2C bus. The system design uses FPGA to build the hardware I2C electrical structure, and uses software to simulate the I2C read and write process required by the video decoder on the PowerPC control motherboard (see Figures 3 and 4 for details), setting its registers to achieve video display functions such as video channel switching and brightness and contrast adjustment, as shown in Figure 5.

Conclusion

The PowerPC MPC8548E microprocessor is favored by embedded system developers for its rich interfaces, strong computing power, fast processing speed, stability and easy scalability. The mainboard of the vehicle display and control system uses this chip as the core processor, equipped with necessary peripheral interfaces, and uses VxWorks as the operating system running on it, so that it has the ability to handle multiple tasks in real time. By expanding PCI devices, data exchange and control between display and control system devices and between the display system and other system devices are realized.