Nor flash life and failure mode test

The Flash life and failure modes were tested several days before the flash file system of djyos was written. From past experiences, we have a basic perceptual knowledge of Flash failure modes. However, we have never tested the flash failure modes, but they are all used by experience and manual. The Flash file system of djyos uses these test results to optimize the file system performance, but does not rely on these test results. First, these test results are not explicitly confirmed by the datasheet device, second, if Flash technology changes in the future, the flash features will no longer match the test results and will not cause fatal errors. Third, the test will not cover all manufacturers and models.
The Flash model tested is sst39vf160. Due to the test time, only four bytes of one slice are tested, it takes a whole week to complete all tests. The test results are summarized as follows:
1. There is a life limit for flash. In sst39vf160, the test results are described as 0.1 million times, the lab film has been tested for more than 0.8 million times.
2. the lifetime of each bit is independent. That is to say, bit1 can still operate normally if bit0 of a byte is invalid.
3. the life cycle of Flash refers to the number of times the flash was rewritten. If one erasure or write operation does not change the content of a single position, this position will not be worn out. For example, if a byte is repeatedly erased and 0xfe is written, the 7-bit high lifetime of the byte will not be affected if bit0 is damaged.
4. After the flash is worn out, it always shows that the flash, it is more and more difficult to erase, but as long as it is cleaned, the write must be correct. However, there is no way to test whether the written data is solid.
5. as long as the original content is 1 bit, it can always be written, however, as long as the original content is 0 bits, only the erased content can be changed to 1.

test data, which repeatedly writes 0 and erased data to a byte, indicates the number of times the data is written to 0.
lifetime of the first unclean Erasure: 876842
lifetime when two consecutive erasure operations are performed for the first time: 1169465
lifetime of the first occurrence of four consecutive erasure attempts: 1769609
lifetime of the first eight consecutive erasure attempts: 1886879