April 19th, 2019, 18:19
High Data Reliability: Flash memory is very reliable and many of the Flash storage device types also include Error Correction Code (ECC) checking and advanced wear leveling.
5.1.24. Wear Level — F5H
The Wear Level command in Table 5-31 is effectively a NOP command and only implemented for backward compatibility with earlier SanDisk SDP series products. The Sector Count Register will always be returned with a 00H indicating Wear Level is not needed.
If security mode feature set is not supported, this (Security Freeze Lock - F5h) command shall be handled as Wear Level command.
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For the CompactFlash Cards that do not support security mode feature set, this (Security Freeze Lock - F5h) command is effectively a NOP command and only implemented for backward compatibility. The Sector Count Register shall always be returned with a 00h indicating Wear Level is not needed. If the CompactFlash Card supports security mode feature set, this command shall be handled as Security Freeze Lock.
1.8.4 Wear Levelling
CompactFlash Memory Card Series products do not require or perform a Wear Level operation. The command is supported as a NOP operation to maintain backward compatibility with existing software utilities.
6.1.23 Wear Level - F5H
This command is effectively a NOP command and only implemented for backward compatability with earlier SanDisk SDP series products. The
Sector Count Register will always be returned with an 00H indicating Wear Level is not needed.
April 19th, 2019, 20:52
April 19th, 2019, 21:32
April 19th, 2019, 22:33
fzabkar wrote:... if these old cards do support internal wear levelling, then what is the purpose of the Wear Level command? What would this command do that the drive itself would not do automatically?
April 19th, 2019, 23:33
fzabkar wrote:fzabkar wrote:... if these old cards do support internal wear levelling, then what is the purpose of the Wear Level command? What would this command do that the drive itself would not do automatically?
Maybe the Wear Level command is intended to query the Level of Wear, ie perhaps the drive responds by reporting the average number of P/E cycles recorded to date ???
April 20th, 2019, 0:46
April 20th, 2019, 2:26
May 13th, 2021, 14:19
May 14th, 2021, 10:24
You will not find the wear level implementation in these source codes. These source codes are bare metal code, without operating system.
Because, usually that will be implemented in the Filesystem along with Operating system.
If you just need the code for reference, you can refer to the JFFS2 filesystem.
processors.wiki.ti.com/.../Create_a_JFFS2_Target_Image
Also, wear leveling algorithms are implemented to prohibit flash memory blocks that contain frequently-altered data from going bad more quickly than those that hold static data. There are two methods to address these requirements: a flash file system and the Flash Transition Layer (FTL). The FTL allows flash devices to be used with unmodified legacy operating systems. It introduces a logical layer above the physical layer that hides the details of flash management from the operating system. USB thumb drives and SD cards utilize an FTL. A flash file system provides better utilization of flash storage at a somewhat higher cost. Two examples of flash file systems are YAFFS, which is used in Google’s Android, and JFFS2, used in the OLPC program. The FTL and flash file system solutions both provide an opportunity to recover old data and metadata after a file is changed or deleted, and the new information is written to a new physical location.
CompactFlash was originally built around Intel's NOR-based flash memory, but has switched to NAND technology
While NOR flash has higher endurance, ranging from 10,000 to 1,000,000, they haven't been adapted for memory card usage. Most mass storage usage flash are NAND based. As of 2015 NAND flash were being scaled down to 16 nm. They are usually rated for 500 to 3,000 write/erase cycles per block before hard failure
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