[ECOS] short reads on serial port..

[ECOS] short reads on serial port..

[Dave Airlie]

Does eCos support short reads? .. I want to read from the serial port for
a max len of 127 bytes, but if there is nothing there I want to
block until something appears .... I suppose I want to use select. .. but
I don't want to use select :-).....

Should I use select, what does it drag in the way of extra stuff to my
build ... I don't want to have to add POSIX stuff really...

Is there another way? 

Thanks,
Dave.

-- 
      David Airlie, Software Engineer, Parthus Technologies plc.,
       Mary Rosse Centre, National Tech Park, Limerick, Ireland.
   t: +353-61-508116 / f: +353-61-508101 / David.Airlie@parthus.com

Re: [ECOS] short reads on serial port..

[Jonathan Larmour]

Dave Airlie wrote:
> 
> Does eCos support short reads? .. I want to read from the serial port for
> a max len of 127 bytes, but if there is nothing there I want to
> block until something appears .... I suppose I want to use select. .. but
> I don't want to use select :-).....
> 
> Should I use select, what does it drag in the way of extra stuff to my
> build ... I don't want to have to add POSIX stuff really...
> 
> Is there another way?

Um, serial reads do block by default. If you want to wait on multiple
devices but avoid select, you could use multiple threads using blocking
reads, which then signal your original thread when data arrives.

Jifl
-- 
Red Hat, 35 Cambridge Place, Cambridge, UK. CB2 1NS  Tel: +44 (1223) 728762
"Plan to be spontaneous tomorrow."  ||  These opinions are all my own fault

Re: [ECOS] short reads on serial port..

[Grant Edwards]

On Thu, Oct 26, 2000 at 08:16:58PM +0100, Jonathan Larmour wrote:

> > Should I use select, what does it drag in the way of extra stuff to my
> > build ... I don't want to have to add POSIX stuff really...
> 
> Um, serial reads do block by default. If you want to wait on multiple
> devices but avoid select, you could use multiple threads using blocking
> reads, which then signal your original thread when data arrives.

Does the serial driver support select?

-- 
Grant Edwards
grante@visi.com

Re: [ECOS] short reads on serial port..

[Dave Airlie]

k> > Should I use select, what does it drag in the way of extra stuff to
my
> > build ... I don't want to have to add POSIX stuff really...
> > 
> > Is there another way?
> 
> Um, serial reads do block by default. If you want to wait on multiple
> devices but avoid select, you could use multiple threads using blocking
> reads, which then signal your original thread when data arrives.
>

yes but they block for the number of bytes you request .. so if I want a
max of 127 bytes they block up to 127 bytes, they can't return when they
get data.. I know I could probably could some mess with reading 1 byte and
then checking how much was left .. but I'd say it would be a bit messy ...

Dave.


 > Jifl
> 

-- 
      David Airlie, Software Engineer, Parthus Technologies plc.,
       Mary Rosse Centre, National Tech Park, Limerick, Ireland.
   t: +353-61-508116 / f: +353-61-508101 / David.Airlie@parthus.com

Re: [ECOS] short reads on serial port..

[Jonathan Larmour]

Grant Edwards wrote:
> 
> On Thu, Oct 26, 2000 at 08:16:58PM +0100, Jonathan Larmour wrote:
> 
> > > Should I use select, what does it drag in the way of extra stuff to my
> > > build ... I don't want to have to add POSIX stuff really...
> >
> > Um, serial reads do block by default. If you want to wait on multiple
> > devices but avoid select, you could use multiple threads using blocking
> > reads, which then signal your original thread when data arrives.
> 
> Does the serial driver support select?

In CVS, yes it should.

Jifl
-- 
Red Hat, 35 Cambridge Place, Cambridge, UK. CB2 1NS  Tel: +44 (1223) 728762
"Plan to be spontaneous tomorrow."  ||  These opinions are all my own fault

Re: [ECOS] short reads on serial port..

[Jonathan Larmour]

Dave Airlie wrote:
> 
> k> > Should I use select, what does it drag in the way of extra stuff to
> my
> > > build ... I don't want to have to add POSIX stuff really...
> > >
> > > Is there another way?
> >
> > Um, serial reads do block by default. If you want to wait on multiple
> > devices but avoid select, you could use multiple threads using blocking
> > reads, which then signal your original thread when data arrives.
> 
> yes but they block for the number of bytes you request .. so if I want a
> max of 127 bytes they block up to 127 bytes, they can't return when they
> get data.. I know I could probably could some mess with reading 1 byte and
> then checking how much was left .. but I'd say it would be a bit messy ...

Well, a bit yes. The eCos version of select itself should be quite
efficient. The problem is that it operates on fd's so that pulls in all the
other file I/O stuff, plug-in filesystem support, devfs etc.

Maybe you'd find it easier just to hack
io/serial/current/src/common/serial.c and change every mention of
cyg_selwakeup() to some function of your own.

Jifl
-- 
Red Hat, 35 Cambridge Place, Cambridge, UK. CB2 1NS  Tel: +44 (1223) 728762
"Plan to be spontaneous tomorrow."  ||  These opinions are all my own fault