What is the difference between norflash and nandflash

1. Interface comparison

NorFlash With universal SRAM Interface , It can be easily attached to CPU The address of 、 On the data bus , Yes CPU Low interface requirements .

NandFlash Devices use complex I/O To access data serially ,8 Two pins are used to transmit control 、 Address and data information . Due to the complexity of time sequence , So general CPU It's better to integrate NAND controller . In addition, due to NandFlash Not attached to the address bus , So if you want to use NandFlash As the startup disk of the system , Need CPU It has special functions , Such as s3c2410 After being chosen as NandFlash Start mode will be automatically read when power on NandFlash Of 4k Data to address 0 Of SRAM in . If CPU It doesn't have this special function , Users cannot run directly NandFlash The code on , That can be done in other ways , For example, many use NandFlash In addition to using NandFlash outside , I also used a small piece NorFlash To run the startup code .

2. Capacity and cost comparison

Compared with NandFlash Come on ,NorFlash Small capacity , Generally in 1~16MByte about , Some new technologies use chip stacking technology to NorFlash The capacity should be larger . In terms of price ,NorFlash comparison NandFlash Say higher , For example, there is a lot of 4Mbyte Of AM29lv320 NorFlash The retail price is 20 yuan , And a piece of 128MByte Of k9f1g08 NandFlash The retail price is 30 yuan .

NandFlash The production process is simpler ,NAND The structure can provide higher capacity within a given die size , This will reduce the price accordingly .

3. Reliability comparison

NAND The bad blocks in the device are randomly distributed , There have been efforts to eliminate bad blocks before , But the yield is too low , The price is too high. , It's not worth it at all .NAND The device needs to scan the medium to find the bad block , And mark the bad block as unavailable . In fabricated devices , If this cannot be done by reliable means , Will result in a high failure rate . The bad block problem is NorFlash It doesn't exist .
stay Flash Bit flip （ One bit Bits flip ） Phenomenally ,NAND Is more likely to occur than NorFlash Much more . The question is Flash It's fatal to store critical files , So it's using NandFlash It is recommended to use at the same time EDC/ECC And so on .

4. Life comparison

stay NAND The maximum number of erasures per block in flash memory is one million , and NOR The number of erasures is 100000 . The lifetime of flash memory is also related to the mechanism of file system , The file system is required to have a loss balancing function .

5. Upgrade comparison

NorFlash The upgrade of is more troublesome , Because of different capacities NorFlash Your address line needs are different , So we are replacing with different capacity NorFlash The chip is inconvenient . We usually solve this problem by making some jump resistors on the address line of the circuit board , For different capacities NorFlash.

And different capacity NandFlash The interface of is fixed , So the upgrade is simple .

6. Read and write performance comparison

Write operations ： whatever flash The device can only be written in empty or erased cells .NAND It is very simple for the device to perform erase operation , and NOR Before erasing, all the bits in the target block must be written as 1. erase NOR The device is based on 64～128KB It's done in blocks , Perform an erase / The write operation takes approximately 5s. erase NAND The device is based on 8～32KB It's done in blocks , Perform an erase / At most, the write operation only needs 4ms.

Read operations ：NOR Reading speed ratio of NAND fast .

7. File system comparison

Linux The system uses MTD To manage different types of Flash chip , Include NandFlash and NorFlash. Support in Flash Common file systems running on are cramfs、jffs、jffs2、yaffs、yaffs2 etc. .cramfs The file system is read-only . If you want to Flash Implement read and write operations on , Usually in NorFlash We will choose jffs And jffs2 file system , stay NandFlash Choose from yaffs or yaffs2 file system .Yaffs2 The file system supports large pages （ Greater than 512 byte / page ） Of NandFlash Memory .