On Fri, 15 Nov 2019 13:35:22 -0800 (PST), in
gmane.comp.hardware.beagleboard.user
[email protected] wrote:
>I am in need of a global variable(s) to store encoder data on a few motors
>that I have attached to my beaglebone. In the event of a power down, I need
>to be able to recall the last encoder position (since it is not absolute)
>of a particular motor. I would like to find a few free memory bocks on the
>eMMC and send a streaming update to it as the motor moves.
>
The eMMC contains a /file system/ -- one does not access raw blocks.
Open a file in modify mode;
loop
write the set of encoder values;
flush the file;
seek(0)...
or maybe mmap with a backing file, as that would allow writing each encoder
as it is moved, rather than all encoders at once.
https://linux.die.net/man/2/mmap
https://linux.die.net/man/2/msync
Note that both (file/flush/seek and mmap/msync methods will invoke a
lot of flash memory write overhead as everytime you change a value the
flash has to allocate a new/erased block, copy unaffected data to it, write
changed data...
Also note that on unintended power-down, you risk corrupting the file
system with partial writes... With luck the journal will catch these and
allow reasonable recovery.
--
Dennis L Bieber
--
For more options, visit http://beagleboard.org/discuss
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