Bootloader Description

Bootloader for embedded development is bound to touch a concept, it is embedded College two courses in the embedded linux system in the development of important content. This article mainly explains the basic concepts and CY7C1329-100AC datasheet and internal Bootloader principle, this part of the master development will be embedded linux system was extremely helpful!

Bootloader definition: Bootloader is executed before the operating system is running a short program, through this short process, we can initialize the hardware devices, the establishment of a mapping table memory space in order to establish appropriate systems hardware and CY7C1329-100AC price and software environment, called the operating system kernel for the final preparation. Meaning that if we want an operating system up and CY7C1329-100AC suppliers and running on our board, we must first of all on board some of our basic configuration and initialization before it can come in to run the operating system boot. Bootloader specific in what actions to complete the analysis we will be back to where we first recall the architecture of PC: PC, boot loader in the BIOS and the hard disk from MBR in OS Boot Loader (such as LILO and GRUB, etc.) with the composition, BIOS hardware detection and the completion of the allocation of resources, will be hard to read MBR Boot Loader in the system RAM, then transfer control to the OS Boot Loader. Boot Loaders main task is to run the kernel image will be read from the RAM disk, and then jump to kernel entry point to run, which started operating system. In embedded systems, often as not, as the firmware BIOS (Note: some embedded embedded cpu will start a short program), so start the task of loading the whole system is completely done by the Boot Loader. For example, in an embedded ARM7TDMI core-based systems, the system is powered on or reset is usually started from the address at 0x00000000, and in this address is usually arranged at the system Boot Loader program. (First think about, general PC and embedded system why there is such a difference here then?)

Bootloader is based on the specific hardware platform to achieve, therefore virtually impossible for all of the embedded system the establishment of a common Bootloader, different processor architectures have different Bootloader, Bootloader not only dependent on the cpu architecture, but also on board-level embedded system device configuration. For two different board, even if they use the same processor, to get on the board running in a Bootloader program can be run on another piece of board, generally need to modify the source code Bootloader.

Bootloader boot methods

Bootloader boot methods are network boot mode Flash boot disk boot mode and manner.

1, the network boot method





Figure 1 Bootloader Network Starting method diagram

shown in Figure 1, which the host and target board, among them over a network connection, the first target of the DHCP / BIOS Bootloader through the BOOTP service to assign IP addresses, configure the network parameters, in order to support the network transmission function. We use the u-boot can set network parameters, so there would not have a way to use DHCP dynamic allocation of IP was. Bootloader next target board kernel image via TFTP service to download to the target board and then through the network file system to create the host and target communication process between the documents, after the system update usually use this mode of Boot Loader . Work in this mode of Boot Loader to its end users usually provide a simple command line interface.

2, disk boot method

this approach is mainly used in desktop computers and servers, these computers are using the BIOS boot, and use the disk as a storage medium, there is Two important are used to start the linux LILO and GRUB, not specifically described here.

3, flash boot mode

This is the most common way. Flash NOR Flash and NAND Flash has two. NOR Flash can support random access, so the code can run directly in Flash, Bootloader is generally stored in the Flash chip. Flash also has stores on the parameters, the kernel image and file system. This starts with the network boot mode difference between the way is that, in the network boot mode, kernel image and file system on the host first, and then transmitted through the network to download into the target board, which started in the way the kernel image and file system is placed directly in Flash, these two points we use u-boot is used a process.