The difference between mini2440 nand flash and nor flash boot

 Nor  flash has its own address lines and data lines, and can use random access methods similar to memory.  Programs can be run directly on nor flash, so nor  flash can be used directly for booting.  When using nor flash to boot, the address will be mapped to 0x00. mini2440 directly burns vivi on nor  flash.

 NAND  flash is an IO device. The data, address, and control lines are all shared. The software area is required to control the read timing. Therefore, it cannot be  randomly accessed like NOR flash and memory, and cannot have EIP (on-chip operation). Therefore, it cannot be used directly as a boot.

S3C2440  burns the boot loader to nand  flash for startup, because there is a built-in SRAM in S3C2440, called stepping  stone (very vivid...), after the system is powered on,  the first 4KB of the content on nand flash will be copied to SRAM for execution, thus realizing  the boot from nand flash. If the bootloader is less than 4KB (like vboot), it can be booted in SRAM, if it is larger than 4KB (u-boot, vivi), after some basic initialization in SRAM, the rest of the bootloader will be copied to SDRAM (>0x30000000).

//==================================================================//Note: The bootloader is a small program that runs before the operating system kernel runs. Through this small program, we can initialize the hardware devices and establish a mapping of the memory space, so as to bring the system's hardware and software environment to a suitable state, so as to prepare the correct environment for the final call to the operating system kernel. Usually, the bootloader is heavily dependent on the hardware to be implemented, especially in the embedded world. Therefore, it is almost impossible to build a universal bootloader in the embedded world. Despite this, we can still  summarize some general concepts of Boot  Loader  to guide the design and implementation of user-specific  bootloaders.

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When we use S3C2440, we often  start it through NOR flash and enter the menu of Vivi (the NOR  flash of S3C2440 has been burned with Vivi), and then download other bootloaders to NAND  flash through the USB download function of Vivi. After the download is complete, we  start it through NAND flash to test our boot  loader.

 Nor  flash is suitable for code storage and EIP, while nand  flash is suitable for large-scale data storage.

Nand  flash boot:  The first 4K of nand  flash memory will be automatically loaded into Stepping  stone (internal SRAM buffer), and then the system automatically executes the loaded boot code. This 4K boot code needs to  copy the content in nand flash to SDRAM for execution.  The first 4K space of nand flash is used to store boot code. SDRAM is faster and is used to execute the code of the main program.

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Note: SDRAM (Synchronous  Dynamic  Random  Access  Memory), synchronous dynamic random access memory, synchronization means that  the memory needs a synchronized clock to work, and the internal command sending and data transmission are based on it; dynamic means that the storage array needs to be constantly refreshed to ensure that data is not lost; random means that data is not stored linearly in sequence, but is freely specified to read and write data at the address.

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