Session Mode and Catch-Up Mode#
Use one of these modes to refresh all blocks of eMMC within a certain number of days. The refresh period may be specified by the eMMC vendor or the eMMC lifetime usage model. The mnand_rfsh utility must keep track of the percentage of refresh progress of the eMMC. Consult the following table to identify the eMMC refresh requirements by vendor (assumes a certain temperature profile; contact an application engineer for details).
Vendor |
Refresh period |
How refresh progress is represented |
|---|---|---|
Hynix |
180 days |
Percentage |
Samsung |
90 days |
P/E Cycles |
The utility maintains its refresh progress in a history file, represented as a percentage of the mNAND device’s capacity; 100% represents one full refresh cycle, i.e. a refresh of all blocks that contain data. The command line specifies the path to the history file.
The history file stores a maximum of 250 entries. Since the utility stores one entry per day, the file can keep track of more than six months of data without growing larger than a few kilobytes (KB). Assuming that each entry consumes 40 bytes, the file does not exceed 10 KB.
These example entries show the format of the history file:
15072015093054,@1864.960000,495805381
15072015093155,@1865.010000,445735877
20072015093054,@1865.010000,374432690
Each line in the history file represents one wake-up of the utility. If the utility wakes up more than twice on a given day, though, the first and last entries for that day are retained, and the rest are discarded.
mnand_rfsh makes entries in a log file each time it runs. The format of each line in the log file is:
A string containing the date and time as “ddmmyyyyHHMMSS”
An @ sign followed by the refresh progress percentage
A checksum for the line