[ECOS] The select() method

[ECOS] The select() method

[Nielsen Linus]

Hello!

I recently fetched the latest version of eCos from the CVS .
I am beginning to write a simple character device just to
understand how it is done.

I wonder how the select() method is supposed to be implemented?
What does eCos expect it to do? Is it like poll() in Linux or what?
I can't find a simple character device in the CVS to look at, and
not any docs either.

/Linus

--
Linus Nielsen Feltzing
mailto:linus@haxx.se

Re: [ECOS] The select() method

[Jonathan Larmour]

Nielsen Linus wrote:
> 
> I recently fetched the latest version of eCos from the CVS .
> I am beginning to write a simple character device just to
> understand how it is done.
> 
> I wonder how the select() method is supposed to be implemented?
> What does eCos expect it to do? Is it like poll() in Linux or what?
> I can't find a simple character device in the CVS to look at, and
> not any docs either.

Not a good situation I know. I think the generic serial driver is bound to
be the closest fit to what you are looking for. See
io/serial/current/src/common/serial.c

If you try to blot out the flow control stuff it should be okay. Basically
the driver exports a function like serial_select in its DEVIO_TABLE (see
io/common/current/include/devtab.h). When something calls select on an fd
associated with this driver, then e.g. serial_select is called and
cyg_selrecord() is used to register that this device is being "selected"
for reading/writing/exceptions.

Then at any other point in the driver, when one of the conditions has been
fulfilled to cause something to be woken up by a select, e.g. an rx buffer
going from empty to non-empty, or a tx buffer filling up, then
cyg_selwakeup() is called to indicate this.

Jifl
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