ARM processors are popular around the world, and 32-bit RISC embedded processors have become mainstream in embedded applications and designs. Compared with the 8-bit single-chip microcomputers that are widely used in China, the 32-bit embedded CPU has a great advantage. It brings rich hardware functions and additional performance to the embedded design, making the upgrade of the entire embedded system only through software. The upgrade can be achieved. The 64K software limit that 8-bit processors usually receive does not exist. Designers can choose multi-tasking operating systems at will, and the application software is designed to be complex and huge, which truly reflects the design concept of "hardware software".
What has changed?
At present, there are many engineers familiar with 8-bit processor development in China, and the development tools and means are also very rich, and the price is low. The development of 32-bit processors is quite different from the development of 8-bit processors.
First, real-time multitasking operating systems (RTOS) introduce 32-bit embedded systems.
Due to the rich resources of the 32-bit CPU, the instruction set is relatively large, and the system software is relatively complicated. Therefore, the corresponding RTOS is usually selected during development to schedule each task in the application software. Software design engineers need to learn the new RTOS technology and master the design and debugging methods of the underlying software, system software and application software. This is a new challenge for developers.
Of course, the introduction of RTOS will also bring embedded developers the benefits of modularization and portability of software, and prepare for the engineering management of software.
Second, the hardware interface of the debug has changed.
In the development of 8-bit processors, the in-circuit simulator ICE (In-Circuit-Emulator) is usually used, and the ICE performs simulation and development work by replacing the CPU with a socket or a corresponding fixture. For 32-bit embedded processors, ICE is difficult to work with development tools due to its high clock frequency (50MHZ to 400MHz or more) and complex package formats such as BGA. The CPU manufacturer provides debugging information by means of the boundary scan interface (JTAG port) for developers to develop.
The JTAG port is usually a 14Pin or 20Pin socket. The JTAG debugger (or JTAG emulator) simplifies the design of the product because it can obtain debugging information directly from the CPU, making the price lower than the ICE.
Third, the way the system is developed changes.
For an 8-bit system development, the designer only needs to follow the hardware design and debugging, software (assembly or C language) programming, positioning and guidance, software debugging, system debugging, etc., the development of application software usually After the hardware, and the application package is not universal.
It is different for a 32-bit embedded system. At the same time of hardware design and development, a real-time multitasking operating system environment is required, and software engineers can simultaneously develop and debug application software packages. At the end of hardware debugging, the design and debugging of the BSP (Board Level Support Package) should be performed. After the BSP is debugged, the system software and application software can be coordinated. Usually the development of application software can be done separately. After replacing the CPU or hardware platform, the application package is generic (based on the same RTOS).
So what tools and environments are needed to develop a 32-bit embedded system?
First you need to choose a suitable multitasking operating system.
At present, there are many commercial RTOSs, such as Linux, Nucleus, WinCE, VxWorkx, etc. Users can choose the right one according to the technical requirements and commercial requirements of the system.
Also, choose the appropriate build tool and debugging environment.
Determine which compiler to use based on the RTOS and programming language (C or C++) selected. For ARM series CPUs, the more common are ARM's SDT and ADS, as well as the free GNU.
Many vendors provide the compiler (Compiler), linker (Linker), locator (Locater), simulator (Simulator) and monitor debugger (Monitor Debugger) as a whole to the user. This is often referred to as the Integrated Development Environment IDE (Integrated Development Environment). Choosing an IDE will bring a lot of convenience to debugging.
Also, choose the right JTAG emulator.
One end of the JTAG emulator is connected to the target board through a JTAG connection cable, and the other end is connected to the debugging environment of the host. There are usually three ways to connect to a host. One is the parallel port method, one is the USB port mode, and the other is the network port mode. These three methods are different in terms of code download speed, connection convenience, and debugging resource sharing. Users can choose according to actual conditions such as funding, technical solution requirements, and host environment. In addition, the JTAG frequency is also an important technical indicator affecting the speed of the JTAG emulator. The faster the JTAG emulator, the higher the JTAG frequency.
Similar to the ICE development method, the JTAG emulator also provides logic tracking to ensure hardware debugging and hardware and software joint debugging. This feature requires additional costs and is therefore recommended for purchase only in complex system level development projects.
A good JTAG emulator should also support task level debugging. In addition to its rich debugging capabilities and good debugging interface, its debugging environment should be able to "know" various types of RTOS. In this way, the user can directly operate on various tasks when performing RTOS-based software debugging. If the JTAG emulator cannot support the debugging of the task, it will bring a lot of inconvenience to the software development engineer and affect the development progress.
The development of 32-bit embedded systems has its own unique technical difficulties, so developers must be fully psychologically prepared and respond accordingly.
BSP development and debugging After the hardware debugging is completed, a real-time operating system (RTOS) migration is required. The most important of these is the development and debugging of BSP. In the entire embedded system, the application software completes various application functions by calling system software. The system software completes the handshake connection with the hardware device through the BSP. Therefore, the performance of the BSP will affect the reliability of the entire system.
Because the development environment provided by the operating system (RTOS) vendor is based on the normal work of the BSP, the user can "see" the entire system hardware resources only after the BSP works normally. Therefore, before this, the user's debugging of the BSP was almost done in "blind". The development and debugging of BSP sometimes takes one to two months or even longer.
There seems to be little solution. First, improve the level of engineers, strengthen the learning in the master of the CPU, the familiarity of the target board hardware and peripheral drive equipment, and the in-depth understanding of the working mechanism of the operating system (RTOS) and the resource allocation of the system; in addition, the good JTAG simulation should be selected. Or other tools.
Parallel development of application software Due to the increasingly rapid rapid market requirements, the development cycle of embedded systems is getting shorter and shorter. This inevitably requires software development at the same time as hardware development. On the one hand, users can develop a part of the software on a standard evaluation board, and then perform system-level debugging and development after the actual target board hardware and BSP are completed. On the other hand, users can use the virtual environment provided by the real-time operating system (RTOS) vendor for software development and debugging. The software to be developed and debugged is almost unlimited. After the actual hardware platform is completed, you only need to recompile the connection and you can download it to the target and run it. Note that the tool environment is added when the RTOS is selected.
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