Arm basics: differences between Nand Flash and Nor Flash

Nand Flash and Nor Flash NOR are characterized by In-chip execution (XIP, eXecute In
Place), so that the application can run directly in flash memory, without having to read the code into the system RAM. The advantage is that you can directly run the program from FLASH, but the process is complicated, the price is relatively expensive, NOR transmission efficiency is very high, in 1 ~ The small size of 4 MB has high cost efficiency, but the low write and erase speeds greatly affect its performance.
The NAND structure provides a very high unit density, achieves a high storage density, and writes and erases quickly. The difficulty of using NAND lies in flash management and special system interfaces. Advantages: large storage capacity and low cost. The disadvantage is that you cannot directly run programs with addressing and can only store data. In addition, NAND
FLASH is prone to bad zones, so verification algorithms are required.
Write operations on any flash device can only be performed in an empty or erased Unit (1) it is very easy for the NAND device to perform the erasure operation, NOR requires that all bits in the target block be written to 1 before erasure. (2) When the NOR device is erased ~ The write/Erase time of a block of KB is 5 s. The erased time of NORFLASHSECTOR varies depending on the brand and size, for example, 4 MFLASH, some SECTOR erasure time is 60 ms, while some require a maximum of 6 S. In contrast, the erased NAND device is composed of eight ~ For 32 KB blocks, it takes up to 4 ms to perform the same operation (3) when selecting a storage solution, the designer must weigh the following factors.
● NOR reads faster than NAND.
● NAND writes much faster than NOR.
● NAND's 4 Ms erasure speed is far faster than NOR's 5s.
● Most write operations require erasure first.
● NAND has fewer erased units and fewer erased circuits. (4) interface differences
NORflash comes with an SRAM interface and has enough address pins to address it, making it easy to access every byte inside it.
NAND devices use complex I/O ports to access data in a serial manner. Different products or vendors may use different methods. Eight pins are used to transmit control, address, and data information. NAND read and write operations use 512 bytes, which is a bit like hard disk management. Therefore, NAND-based memory can replace hard disks or other Block devices. (5) Capacity difference:
NORflash occupies 1 ~ Most of the 16 MB flash memory market, while NANDflash is only used in 8 ~ Among the MB products, this also shows that NOR is mainly used in code storage media, and NAND is suitable for data storage. (6) Reliability and Durability
-Life (durability)
In nand flash memory, the maximum number of writes to each block is 1 million, while that of NOR is 100,000. In addition to having a block erasure cycle of 10 to 1, the typical NAND block size is eight times smaller than that of the NOR device, each NAND memory block is deleted less frequently within a given period of time.
-Bit Switching
All flash devices are plagued by bit switching. If the bit is changed, you must use the error detection/error correction (EDC/ECC) algorithm. The problem of bit inversion is more common in nand flash memory. When using nand flash memory, the EDC/ECC algorithm should be used. Using NAND to store multimedia information is not fatal. Of course, if you use a local storage device to store operating systems, configuration files, or other sensitive information, you must use the EDC/ECC system to ensure reliability.
-Bad Block Processing
The Bad blocks in the NAND device are randomly distributed. The NAND device needs to initialize and scan the media to find the bad blocks and mark them as unavailable. In an existing device, a high failure rate may occur if this processing is not performed in a reliable way. (7) ease of use
NOR-based flash memory can be used very directly. When using the NAND device, you must first write the driver to continue other operations. Writing information to a NAND device requires considerable skill, because designers must not write information to Bad blocks, which means virtual ing must be performed from beginning to end on the NAND device. (8) software support
Running code on the NOR device does not require any software support. When performing the same operation on the NAND device, the driver is usually needed, that is, the memory technology driver (MTD ), the NAND and NOR devices require MTD for write and erase operations.
Fewer MTDS are required to use the NOR device. Many vendors provide more advanced software for the NOR device, including the TrueFFS driver of the M-System, this driver is used by WindRiverSystem, Microsoft, QNXSoftwareSystem, Symbian, Intel, and other vendors. The driver is also used to simulate DiskOnChip products and manage nand flash memory, including error correction, Bad Block Processing, and loss balancing. (9) To use nand flash to store data and programs on a handheld computer, there must be a NOR
FLASH to start. In addition to the SAMSUNG processor, other mainstream processors used in handheld computers do not support direct
Start the FLASH program. Therefore, a small nor flash must be used first.
Start the machine and load the OS and other software from the NAND FLASH into the SDRAM for running. NOR is characterized by In-chip execution (XIP, eXecute In
Place), so that the application can run directly in flash memory, without having to read the code into the system RAM. The advantage is that you can directly run the program from FLASH, but the process is complicated, the price is relatively expensive, NOR transmission efficiency is very high, in 1 ~ The small size of 4 MB has high cost efficiency, but the low write and erase speeds greatly affect its performance.
The NAND structure provides a very high unit density, achieves a high storage density, and writes and erases quickly. The difficulty of using NAND lies in flash management and special system interfaces. Advantages: large storage capacity and low cost. The disadvantage is that you cannot directly run programs with addressing and can only store data. In addition, NAND
FLASH is prone to bad zones, so verification algorithms are required.
Write operations on any flash device can only be performed in an empty or erased unit.