| Bootloader is the first running program after power-on in embedded systems. Its function is to initialize the hardware devices, to establish the system memory space mapping, and finally to finish loading the Linux operating system. This dissertation is about porting bootloader to the Loongson platform. Loongson is a general-purpose CPU designed and developed independently by Institute of Computing Technology Chinese Academy of Sciences. An analysis about the bootloader ported based on the Loongson platform is significant for the promotion and application of domestic CPU.Bootloader has several versions currently, so this dissertation analyzes the advantages and disadvantages of the various versions and selects U-boot as the final object for porting. Because the bootloader porting is very closely related to the CPU architecture, an overview and some necessary details about the Loongson architecture are provided.The start-up phase of different embedded hardware is obviously quite different and U-boot doesn’t provide a complete code about this phase, so this part of the code must be ported according to the characteristics of the specific hardware. In the process of migration a lot of things have to be considered including setting the interrupt vector, initializing the CPU registers, setting up the temporary stack, initializing the memory and cache, moving and relocating Nand blocks, allocating the memory of U-boot, activating the serial support etc. This dissertation also involves the instruction to the hardware related to this porting such as cache and Nand flash. The key points regarding the code porting are elaborated in detail and summarized. The stability of the ported U-boot is also well-verified. The last part of this dissertation gives the prospects for further work.At last, the porting of U-boot based on the Loongson platform is completed, and U-boot works well on the Loongson platform. The experiments show that this ported u-boot performs well and stably. |
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