[ECOS] Re: Waiting I/O operation

Sergei Gavrikov w3sg@SoftHome.net
Mon Jul 23 09:12:00 GMT 2007

В Пнд, 23/07/2007 в 11:05 +0700, Alexey Shusharin пишет:
> Sergei Gavrikov wrote:
> > Hello,
> Hello all,
> I'm not eCos kernel expert but I think we can use cyg_flag_setbits() in 
> DSR level.
> > As I could understand Andrew's main concern, that is, We aren't allowed
> > to block in a DSR (cyg_flag_setbits() do it), and I am agree with him.
> Yes, we can't block in a DSR and IMHO cyg_flag_setbits() doesn't do it.
> If we compare Cyg_Flag::setbits() (in flag.cxx) and 
> Cyg_Condition_Variable::sygnal() (in mutex.cxx) we will see that there 
> are no fundamental differences. So, if we can call sygnal() in a DSR we 
> are able to call setbits() too.
> > I looked at the common hal's drv_api.c against the kernel's flag.cxx. As
> > I could see the cyg_drv_cond_*() calls are almost the atomic funcs. I
> > wouldn't say same thing about the kernel's Cyg_Flag::setbits().
> drv_api.c is the implementation of driver API in configuration without 
> kernel. If we use a kernel, directives in dri_api.h select kapi.c 
> implementation (kernel C API). And we use code from mutex.cxx and other 
> kernel code eventually.
> > More that, I liked cyg_drv_cond_wait(), because that is just it
> > 
> > while (cond->wait == 1) { call_dsrs (); }
> > 
> > So, my application can be a kernel-less application too. I think the
> > table from Chapter 13 is a good guide-line: a what allowed us to run
> > from DSR:
> > 
> > http://ecos.sourceware.org/docs-latest/ref/devapi-synchronization-levels.html
> Yes, if you use functions from drv_api.h only, your application can be a 
> kernel-less. And this is the reason why you didn't find using of flags 
> in drivers. It's not recommended because the flag is not included in 
> driver API.


The DSR is a kernel driven stuff. As I understood before... The eCos
scheduler manages the deffered service routings. So, it was no sence to
mention the DSRs in kernel-less environment at all. I did it, but I did
correct myself at once :-)


> But I would like to use flags in the application, and I know that kernel 
> exist. So IMHO I can call cyg_flag_setbits() in a function which is 
> called from a DSR.
> Best regards
> Alexey Shusharin

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