Joined: 09 Dec 2008 Posts: 1531
Location: RecoverMyFlashDrive.com Fairfield, CT, USA
Posted: Sun Feb 16, 2020 0:53 Post subject: Reading Bad Quality Chips
Currently there is a big problem with reading chips with good quality dump.
What are some IDs of NAND chips that are having issues?
Has adjusting the Vcc helped?
Has Read Retry helped?
My antidotal notes and thoughts not backed up with fact:
WL Toshiba / SanDisk:
Erasing a block doesn’t set all bits to 1 or 0, instead most of the bits are set to 1 or 0. (See picture).. FE gets stuck on these trying to process the data.
My solution: Count the state of bits in the first 128bits of a block, if its more than 85% either way disregard the block and fill the block with set bits.. its a variable percentage but my reasoning is XOR distributes the number of bits, if the distribution is bad the underlying data is probably bad. This greatly speeds up FE on applicable cases (eg: SanDisk)
Variable Voltage: Do Toshiba/SanDisk NAND work with the Power Adapter? From memory every time I've tried I get an ID of 0x00ffffff, ?? Do Toshiba Chips NOT start up Tri-State ??.. From memory covering Vcc pin on the NR and supplying external voltage (eg: 2.55v) only works for monolithics, especially monolithics where the controller powers up when external 3.3v is applied sending spurious data to the NR..
Constant Voltage: Some Toshiba/SanDisk NAND chips need voltage applied to pins not supported by TSOP-48 adapter v3... eg WP or 16bit I/O.. This must be done manually.
Many of these chips need Read Retry Modes and the applicable registers vary by ID however its implementation would be complicated. Specifically, unlike SanDisk or Intel where a Read Retry mode is generally valid for an entire bank.. Hynix Read Retry modes are only valid for a page (upper, middle, lower), block, or plane. If a bad page is encountered every read retry mode is cycled through to find a good value. Currently the only option is ECC combine however it's not efficient. I haven't had any luck using different voltages but I haven't done any extensive testing with Power Adapter v3 so I might be wrong..
My Solution: Use Read Retry Codes in Segments and merge the files together..
Intel / Micron:
Variable Voltage - Use Power Adapter
Also sometimes I think it must be acknowledged the the chip might just be bad.
Does anyone else have any antidotal input on bad quality chips?