fstorage: writting and then reading 'wrong' data?

RE: fstorage: writting and then reading 'wrong' data?

Alex Co — Wed, 05 Jun 2019 14:23:23 GMT

Same output, I meant this:

fstorage example started.
SoftDevice is present.
Initializing nrf_fstorage_sd implementation...
Done.Reading "746f6e20" from flash.
Template example started.

which means that even if I just read, the value read is not ffffffff (last written). That could be justified by: as I never did an erase, and tried to write lots of things i could never get the expected vaue (ffffffff) because of the reason pointed by Jorgen.

Now If I erase and then if I write ffffffff and can read ffffffff! :-)

Solved!

I was missing that flash property about "A flash write operation can only change bits from 1 to 0, to change a 0 to a 1 requires a erase operation,"

Thanks to all

Alex

RE: fstorage: writting and then reading 'wrong' data?

Andy — Wed, 05 Jun 2019 12:34:24 GMT

Well of course you're going to get the same output if you read twice the same address without writing in between. What did you expect?

RE: fstorage: writting and then reading 'wrong' data?

Alex Co — Wed, 05 Jun 2019 12:15:51 GMT

I tried to read without writing in the same iteration but got the same output.

I have just an array to write so I am going to try to erase the page always before writing the array and find out if the problem is that. It could be that reason as I never erase page and I have tested with different contents for array

Thanks

RE: fstorage: writting and then reading 'wrong' data?

awneil — Wed, 05 Jun 2019 11:48:13 GMT

[quote userid="14926" url="~/f/nordic-q-a/48193/fstorage-writting-and-then-reading-wrong-data/191068"]A flash write operation can only change bits from 1 to 0, to change a 0 to a 1 requires a erase[/quote]

Alex Co: FDS builds on fstorage - including managing stuff like this.

RE: fstorage: writting and then reading 'wrong' data?

Jørgen Holmefjord — Wed, 05 Jun 2019 11:37:12 GMT

Did you try reading the area before writing, to make sure it is empty? A flash write operation can only change bits from 1 to 0, to change a 0 to a 1 requires a erase operation, which again can only be performed on an entire page. Do you get any errors in the result field in the event handler?

RE: fstorage: writting and then reading 'wrong' data?

Alex Co — Wed, 05 Jun 2019 11:25:16 GMT

Ok, I got it, like the preamble in comm messages. Thanks!

What about wrong read data. any ideas?

RE: fstorage: writting and then reading 'wrong' data?

awneil — Wed, 05 Jun 2019 09:43:15 GMT

[quote userid="20031" url="~/f/nordic-q-a/48193/fstorage-writting-and-then-reading-wrong-data"]How Do we know if the flash is being written for the first time or not?[/quote]

The usual way is to write some "marker" pattern:

If the pattern is present, you know that the flash has previously been written;
If the pattern is not present, you know that the flash has not yet been written - so you write the pattern.

This is a common approach with any form of storage - not just Flash, and not specific to Nordic.