Google SOC project tinyRTEMS

[Joel Sherrill]

阎淼 wrote:
> Hello all,
>
>    I  am  interest  in tinyRTEMS project,  I have read the wiki page,
> and there are a lot of work has been done. I would like to know what
> is the direction of Tiny RTEMS project.
>   
As stated, its goal is to shrink the minimum footprint of an RTEMS
executable
and a number of issues have already been addressed. Many of the issues are
fairly subtle and if you are new to RTEMS might be hard to figure out.

One of the larger issues left and probably the only one worth even thinking
about as a GSOC project are the last three on the list.

*disable newlib reentrancy (which might already be partially there)
*disable filesystem
*"device table filesystem". Functionality similar to how device names were
handled in RTEMS 4.0.0. Now we have a real POSIX style filesystem with
devices. Then we had a lookup table which mapped device names into
major/minor. So when you call open(), the device name isn't looked up
in a filesystem, it is looked up in a table of strings.

Many of the TinyRTEMS ideas require the addition of application time
configuration to select the run-time capabilities. This one is a bit harder
because it spans the IO and filesystem infrastructure. You will have to
baseline
the size of the minimum, hello and ticker executables and work to eliminate
filesystem code you are replacing with a lighter alternative.

In minimum, you want to push to have NO filesystem and IO code.

In hello, you want the "device name lookup".

Together the list above looks to be about 1/3-1/2 of the code in the minimum
executable on the ARM/Thumb rtl22xx_t BSP I use as a reference. So even
though
you might only save 8-12K total, you are moving from ~24K to 12-16K minimum.

Does that make sense?


NOTE: Many space based systems using RTEMS do not use the filesystem and
hack it out anyway. This is just providing this reduced functionality
mode as
a real configure option.
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-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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