At the time of development of embedded systems, the first challenge is how to pick a development platform that suits you. The ARM series processor is designed for embedded devices and is the first choice for constructing embedded system hardware platforms. This article will introduce how to choose an embedded development platform for actual needs, how to build a practical development environment, and how to take the first step in embedded Linux system development.
Selection guide
Before the development of embedded systems, you must first choose the appropriate development platform. For experienced developers, of course, you can make your hardware yourself, then select the appropriate embedded Linux system to transplant it to the development platform. But for beginners, a better way is to buy hardware vendors that have been done well and concentrate on the development of applications.
Although the ARM microprocessor has more than a dozen core structure, dozens of chip manufacturers and many functional combinations, but this also brought certain difficulties in determining the plan. Objectively speaking, embedded systems are generally tailored. Developers must choose the right software and hardware platform according to customer needs, otherwise, if you can't complete the required functions, you will have a waste of resources, it is not easy to pick out a suitable plan. Beginners may wish to learn from some of the following experience when making decisions.
ARM has designed a range of microprocessor kernel structures to adapt to the needs of different applications. If the user wants to use the Windows CE or standard Linux and other operating systems to reduce software development time, it is necessary to use ARM chip with memory management unit (MMU) above ARM720T, such as ARM720T, ARM920T, ARM922T, ARM946T, and the like. However, for ARM7TDMI's microprocessor without MMU, only the operating system that does not require MMU support as UCLinux, and the standard Linux cannot be run.
The working frequency of the microprocessor has largely determines the high and low of its computing power. The ARM7 series microprocessor is typically 0.9MIPS / MHz. The common ARM7 chip system main clock is 20MHz to 133MHz; the typical processing speed of the ARM9 series microprocessor is 1.1MIPS / MHz, the common ARM9 chip system master The clock is 100MHz to 233MHz; the typical processing speed of the ARM10 series microprocessor is 1.25MIPS / MHz, and the clock frequency can be as high as 400 MHz. Different ARM chips have different dealing with clocks. Some chips have only one primary clock frequency, while some of the internal clock controllers of some chips can provide different frequencies from Functions such as ARM core, USB, UART, and DSP, respectively.
Most ARM microprocessor sheets have little capacity, and users need to expand external memory when designing embedded systems.
In addition to the ARM microprocessor core, almost all ARM chips have extended the corresponding functional modules according to their different applications, and integrated into the chip, thereby forming the inner and outer peripheral circuit, such as USB interface, I / O Interface, RTC and LCD controllers, etc. The developers of embedded systems should use these peripheral circuits as much as possible to implement the functions required by the system. This can simplify the design of the system and can improve the reliability of the system.
Picking a suitable hardware platform for embedded systems is a very complex work. The above is only some basic principles, and the actual application is also determined according to the situation. The author has compared and identifying the research and development of embedded Linux, and the author uses a development board based on the S3C4510B processor. It is a 16/32-bit RISC microcontroller with a high price-effective, which is a high cost-effective 16/32 RISC microcontroller, which is adopted. Since it has the advantages of high performance, low power consumption, it is particularly suitable for applications where prices and power consumption are more sensitive, such as handheld equipment, network communication, and industrial control.
Get started
Let's take a look at the embedded Linux. If the user's development board is provided by a dedicated hardware manufacturer, it is generally pre-installed with an embedded operating system, such as Windows CE, Palm OS or Linux. The S3C4510B development board described here is pre-installed to embedded Linux. We may wish to borrow it to experience the development method of embedded Linux. If the user's development board is an assembled or bought, other embedded operating systems are pre-installed, then they need to be able to re-build the system. As mentioned earlier, two platforms need to be used when developing embedded systems: one is a development platform (Host), and the other is a target platform (Target). The development platform usually serves as a common PC. It can be connected to the target platform by serial port, parallel port, and Ethernet, etc., thereby collecting a basic development environment of an embedded system. For embedded Linux systems, the simplest development environment only needs to be used to host, target boards, and serial connectors.
When the hardware is connected, the next thing to do is to establish a connection between the host and the target board. This requires running a terminal emulator on the host. LINUX is not Minicom. Minicom is an interface-friendly, and easy to use serial communication programs that make it easy to monitor or control serial ports, which is a very important component of the embedded Linux development environment. People who are slightly learned from serial communication know that it is more troublesome when serial communication is the setting of communication parameters. Fortunately, MINICOM provides a very friendly configuration interface, which will enter the configure interface of Minicom by performing the following command.
# minicom -s
Select the Serial Port Setup item from the menu to enter the serial port configuration interface. The user then selects the correct serial device file, baud rate, data bit, stop bit, parity bit, hardware flow control, and software stream control parameters based on the specific conditions of the development board used. The parameters selected in FIG. 4 represent the serial port 1 (/ dev / ttys0), the baud rate is 19200 bps, the data is 8 bits, no parity bit, stop 1 bits, no hardware flow control, and no software control.
After setting the parameters of serial communication, returns to the MINICOM's primary configuration interface; then select the Save Setup AS DFL item to save the current configuration value; then select the exit from minicom to exit Minicom.
If everything is normal, you can use Minicom to build normal communication with the development board. First, execute the following command to enter Minicom again:
# minicom
Then turn on the power supply on the development board or press the reset key on the development board, you can monitor the pre-running state of the embedded Linux system on the development board in Minicom. MINICOM imagination can be an embedded Linux system on the development board, that is, all commands entered in Minicom will be handled by the embedded Linux system on the development board.
summary
Building an embedded system's primary task is to clarify what it will do. The use of the entire behavior pattern and architecture of the embedded system, and also determines the hardware platform and software platform it should adopt. Picking the target platform for embedded systems must be cautious, as this involves there is no good development environment and technical support, be sure to select the appropriate processor, the appropriate development board and the appropriate development environment based on the actual situation. Please keep in mind a point when developing embedded systems, and user needs will always be "first driving force" of embedded systems.
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ARM processor profile
ARM (Advanced Risc Machines) is located in the British Cambridge, main business is a 16-bit and 32-bit embedded microprocessor. However, it does not produce and sells chips, but the use of technical authorization, allowing other semiconductor manufacturers to make ARM microprocessor manufacturing.
