Use U-boot to change a bit in NAND flash memory - u-boot

Question

I am trying to test the ECC (error correction code) in U-boot. To do so, I want to use U-boot to flip a bit in NAND flash without rewriting the CRC. Then, when I restart the processor, I hope to see U-boot correct the bit using ECC.
The question is how can I write a new bit or byte or page into memory using U-boot without writing a new CRC?

Answer 1

Never found a u-boot with the bitterr implementation, the source code usually looks like this:
if (strcmp(cmd, "biterr") == 0) {
/* todo */
return 1;
}
In this case, the way to go is little more complicate. As it took me some time to discover how to do it, I believe it may be helpful for other to have the manual process described here.
nand read ${ram_addr1} ${sector_addr} ${sector_size}
nand read.oob ${ram_addr2} ${sector_addr} ${oob_size}
nand erase ${sector_addr} ${sector_size}
nand write ${ram_addr1} ${sector_addr_plus_page_size} ${sector_size_minus_page_size}
cp ${ram_addr2} ${ram_addr1} ${oob_size}
mm ${ram_addr1_plus_biterr_offset}
#modify a single bit of the referred data
nand write.raw ${ram_addr1} ${sector_addr} 1
Check if you get a bitflip err message:
nand read ${ram_addr1} ${sector_addr} ${sector_size}
Note that you may set the environment to run this command as is, or replace the ${} directives for the raw values. ram_addr1 and ram_addr2 may be any available ram adrress as long as ram_addr2 - ram_addr1 > sector_size

Answer 2

Use nand biterr to simulate a bit flipping at an offset.
For example, bit 3 in byte 69 [0x45] in the 2nd block = 0x20000
U-Boot> nand biterr 0x20045 3
Erasing at 0x20000 -- 100% complete.
toggling bit 3 in byte 45 in block 20000 00 ->08
byte offset 0x00020045 toggled bit 3
Reference:
http://www.infopoort.nl/index.php/Software:U-Boot

Answer 3

You can use nand read.raw and nand write.raw which by passes the writing to the OOB.

Answer 4

To simplify #Jonatan-Goebel answer, you can avoid a lot of the steps as long as you only clear bits, as this won't require erasing the nand.
=> setenv ram_addr1 $loadaddr
=> setenv page_addr 0
=> setenv page_size 1000
# Make sure there is actually something in nand
=> nand erase.chip && mw.b $loadaddr ff 40000 && load mmc 0 $loadaddr MLO && nand write.i $loadaddr $page_addr $filesize
# Read one raw page
=> nand read.raw ${ram_addr1} ${page_addr} 1
# Clear x number of bits
=> mm $ram_addr1
83000000: 00000040 ?
...
83000018: 4e495454 ?
8300001c: 00005347 ?
83000020: ffffffff ? efffffff
83000024: ffffffff ? => <INTERRUPT>
# Write back page
=> nand write.raw ${ram_addr1} ${page_addr} 1
# Read the page
=> nand read ${ram_addr1} ${page_addr} ${page_size}
NAND read: device 0 offset 0x0, size 0x40000
elm_config: 2
nand: bit-flip corrected #data=35
262144 bytes read: OK
Make sure you try again with too many bitflips to make sure it fails
...
=> mm $ram_addr1
...
83000020: cccccccc ? 8ccccccc
83000024: ffffffff ? => <INTERRUPT>
=> nand write.raw ${ram_addr1} ${page_addr} 1
NAND write: 4320 bytes written: OK
=> nand read ${ram_addr1} ${page_addr} ${page_size}
NAND read: device 0 offset 0x0, size 0x40000
elm_config: 2
omap-elm: uncorrectable ECC errors
NAND read from offset 0 failed -74
0 bytes read: ERROR