How to read file directly from compact flash?

andaya · 11-27-2012, 08:07 AM

Hello,

I notice when I read a file in linux or more easy, if I make "cat file_from_CF", the first time read from compact flash ( light status is blinking ), but if I repeat operation again, light status does not blink (I think its read from a cache or similar) .

Is there any way to force read directly from compact flash??

I have a embedded system and I would like to make a program to read a file every 1 sec to find read problems.

Best regards.

theNbomr · 11-27-2012, 08:52 AM

What makes you think the read from cache will be incorrect? A good rule of thumb is to not try to outsmart the filesystem. If the file has been modified since your last read, the filesystem will know, and either read from the block device media, or will have updated the cache accordingly. There may be options available for your filesystem to disable caching. If you think there is a problem is with the block device, you can read and write it directly.

--- rod.

andaya · 11-27-2012, 09:06 AM

Quote:

Originally Posted by theNbomr

What makes you think the read from cache will be incorrect? A good rule of thumb is to not try to outsmart the filesystem. If the file has been modified since your last read, the filesystem will know, and either read from the block device media, or will have updated the cache accordingly. There may be options available for your filesystem to disable caching. If you think there is a problem is with the block device, you can read and write it directly.

--- rod.

Hello rod,

I dont think the read from cache is incorrect.
I would like to test IDE adapter because sometimes, I have some boards that ide adapter is not soldier correctly, and return me some read problems.

For example, I find some options:

open() with O_DIRECT flag to acces directly to CF, for example.
Is there other way to do it? for example, fopen().

Best regards.

theNbomr · 11-27-2012, 10:41 AM

The filesystem will just get in the way. You should not mount the filesystem, and just use the block device (/dev/hdxx) directly in order to diagnose problems. Or, better still, access the hardware directly, either from userspace or with a kernel-mode diagnostic (that you will most likely have to write).

--- rod.