[ECOS] mutex operation

[ECOS] mutex operation

[Andy Simpkins]

Hi there,

Just a short question on the use of Mutexes as the documentation does not
seam clear...

If I use a mutex to protect a resource in both a thread and inside a DSR
will the eCos scheduler promote the thread's priority to greater than that
of the DSR in the event that the
thread has locked the resource and the DSR is waiting on that resource?


Andy

Re: [ECOS] mutex operation

[Hugo Tyson]

"Andy Simpkins" <Andy.Simpkins@TardisMobile.com> writes:
> Just a short question on the use of Mutexes as the documentation does not
> seem clear...
> 
> If I use a mutex to protect a resource in both a thread and inside a DSR
> will the eCos scheduler promote the thread's priority to greater than
> that of the DSR in the event that the thread has locked the resource and
> the DSR is waiting on that resource?

Nope.  You must not use a mutex within a DSR, because attempting to acquire
the mutex can cause the caller to block.  DSRs must not block.

Priority does not really apply to DSRs and interrupts:

All interrupts (ISRs) (when enabled and unmasked) have higher priority than
all DSRs and all threads.
All DSRs have higher priority than all threads.
Threads have numerical priority amongst themselves.
Depending on hardware implementation, interrupts might have a numerical
proprity amongst themselves - more often it is fixed by the hardware.
DSRs are just all run in arbitrary order as soon as possible, as soon as it
is safe to do so.

HTH,
	- Huge

RE: [ECOS] mutex operation

[Andy Simpkins]

Thanks,

I agree that I can't use cyg_mutex_lock and cyg_mutex_unlock, but surly
there has to be a method of sharing a resource for use by a DSR and thread?

I could in this instance fall back to getting a thread to do the job passing
data through a message box, but it would mean that I need to create yet
another thread to do nothing more complex than write a few bits to
hardware....

Any suggestions would be most welcome

Andy

> -----Original Message-----
> From: ecos-discuss-owner@sources.redhat.com
> [ mailto:ecos-discuss-owner@sources.redhat.com]On Behalf Of Hugo Tyson
> Sent: 03 July 2001 14:56
> To: eCos Disuss
> Subject: Re: [ECOS] mutex operation
>
>
>
> "Andy Simpkins" <Andy.Simpkins@TardisMobile.com> writes:
> > Just a short question on the use of Mutexes as the
> documentation does not
> > seem clear...
> >
> > If I use a mutex to protect a resource in both a thread and inside a DSR
> > will the eCos scheduler promote the thread's priority to greater than
> > that of the DSR in the event that the thread has locked the resource and
> > the DSR is waiting on that resource?
>
> Nope.  You must not use a mutex within a DSR, because attempting
> to acquire
> the mutex can cause the caller to block.  DSRs must not block.
>
> Priority does not really apply to DSRs and interrupts:
>
> All interrupts (ISRs) (when enabled and unmasked) have higher
> priority than
> all DSRs and all threads.
> All DSRs have higher priority than all threads.
> Threads have numerical priority amongst themselves.
> Depending on hardware implementation, interrupts might have a numerical
> proprity amongst themselves - more often it is fixed by the hardware.
> DSRs are just all run in arbitrary order as soon as possible, as
> soon as it
> is safe to do so.
>
> HTH,
> 	- Huge
>

RE: [ECOS] mutex operation

[Andy Simpkins]

Doh!

there is a perfectly good example in the serial port handling...

thread locks resource using a mutex
thread disables DSRs
thread does it's thing with the resource
thread re-enables DSRs
thread unlocks resource' mutex

thus no other thread can access the resource
DSRs can not access the resource whilst it has been grabbed by a thread
(because they are disabled)

Andy


> -----Original Message-----
> From: ecos-discuss-owner@sources.redhat.com
> [ mailto:ecos-discuss-owner@sources.redhat.com]On Behalf Of Andy Simpkins
> Sent: 03 July 2001 15:19
> To: eCos Discuss
> Subject: RE: [ECOS] mutex operation
>
>
> Thanks,
>
> I agree that I can't use cyg_mutex_lock and cyg_mutex_unlock, but surly
> there has to be a method of sharing a resource for use by a DSR
> and thread?
>
> I could in this instance fall back to getting a thread to do the
> job passing
> data through a message box, but it would mean that I need to create yet
> another thread to do nothing more complex than write a few bits to
> hardware....
>
> Any suggestions would be most welcome
>
> Andy
>
> > -----Original Message-----
> > From: ecos-discuss-owner@sources.redhat.com
> > [ mailto:ecos-discuss-owner@sources.redhat.com]On Behalf Of Hugo Tyson
> > Sent: 03 July 2001 14:56
> > To: eCos Disuss
> > Subject: Re: [ECOS] mutex operation
> >
> >
> >
> > "Andy Simpkins" <Andy.Simpkins@TardisMobile.com> writes:
> > > Just a short question on the use of Mutexes as the
> > documentation does not
> > > seem clear...
> > >
> > > If I use a mutex to protect a resource in both a thread and
> inside a DSR
> > > will the eCos scheduler promote the thread's priority to greater than
> > > that of the DSR in the event that the thread has locked the
> resource and
> > > the DSR is waiting on that resource?
> >
> > Nope.  You must not use a mutex within a DSR, because attempting
> > to acquire
> > the mutex can cause the caller to block.  DSRs must not block.
> >
> > Priority does not really apply to DSRs and interrupts:
> >
> > All interrupts (ISRs) (when enabled and unmasked) have higher
> > priority than
> > all DSRs and all threads.
> > All DSRs have higher priority than all threads.
> > Threads have numerical priority amongst themselves.
> > Depending on hardware implementation, interrupts might have a numerical
> > proprity amongst themselves - more often it is fixed by the hardware.
> > DSRs are just all run in arbitrary order as soon as possible, as
> > soon as it
> > is safe to do so.
> >
> > HTH,
> > 	- Huge
> >
>
>