NAND bad blocks
NAND memory apparently gets shipped with blocks that are already bad. The vendor just marks those blocks as bad, thus resulting in higher yield and lower per-unit cost.
The only block that is guaranteed to be good, is the first block (first 16kBytes).
We are also guaranteed that a minimum of 4016 blocks (out of the 4096) are good. This means up to 80 blocks (320kBytes) can be dead.
The solution is split into various pieces
The boot loader itself contains a small first-stage boot loader for the S3C2410 Steppingstone.
This code (which Harald wrote in ARM assembly) needs to be altered to detect and skip bad blocks. At this time, the bootloader could itself extend over bad blocks. However, how do we first flash the bootloader into NAND? The JTAG flashing program has no support for detecting bad blocks.
The kernel is contained in its own partiton QT2410#NAND. We have to flash it using the
command, and read it later again via
command. Those two variants (as opposed to their non-".e"-postfixed versions) simply skip bad blocks
The root filesystem uses JFFS2, which is already bad block tolerant. It, too, has to be written using the
command in u-boot
sjf2410 (during development)
The sjf2410-linux tool has a compile-time option to check (and skip) bad blocks. If we use this for flashing u-boot, we will preserve the bad block info, once u-boot steppingstone code has been enhanced to skip bad blocks.
I have no idea how flashing during the production process is supposed to happen.
Tentative new Flash memory layout
start size name 0x00000000 0x00030000 196KB u-boot 0x00030000 0x00004000 16KB u-boot environment 0x00034000 0x00200000 2MB kernel 0x00234000 ... jffs2