Re: What are the __retarget_lock functions?

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

On 10/09/2018 10:53, Freddie Chopin wrote:
> On Sun, 2018-09-09 at 10:59 +0200, Thomas Kindler wrote:
> > There are some things I'm not yet happy with:
> >
> > 1. Each lock takes about 80 bytes
> This is easily solvable (; Just stop using FreeRTOS (;
>
> OK, but seriously. This is a consequence of FreeRTOS design, where
> "everything is a queue". Your mutex is in fact a queue with length
> zero, so it has dozens of useless member variables, which finally add
> up to ~80 bytes. In my opinion (which is of course biased and
> subjective), this design decision is extremely stupid.
>
> In other RTOSes (including distortos - the one I'm writing), the mutex
> is usually ~20-24 bytes long, so it's ~3-4x smaller, while having a lot
> more features (like selectable protocol or selectable type).

The 80 bytes for a mutex object are quite a lot. Even on RTEMS, which 
supports SMP systems and complex locking protocols, a recursive mutex 
needs just 24 bytes (32-bit target):

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=blob_plain;f=newlib/libc/sys/rtems/include/sys/lock.h;hb=HEAD

On a uniprocessor RTOS two or three pointers and an integer should be 
enough to implement a recursive mutex with support for priority inheritance.

--
Sebastian Huber, embedded brains GmbH

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