Re: [ECOS] Device driver open & close

[Andrew Lunn <andrew at lunn dot ch>]

>> This gets called for each open?

Yes. Take a look at the code:
io/fileio/current/src/devfs.cxx:dev_open() calls cyg_io_lookup() on
the device. And then there is this comment:

//
// Look up the devtab entry for a named device and return its handle.
// If the device is found and it has a "lookup" function, call that
// function to allow the device/driver to perform any necessary
// initializations.
//

Cyg_ErrNo
cyg_io_lookup(const char *name, cyg_io_handle_t *handle)

>>> You might be better using cyg_io_set_config() mechanism to turn it on
>>> and off.
>>>   
>> This is unfortunate. For another example, the system will have the  
>> ability to power down the compact flash drive(s). Which order should  
>> the power down happen?
>> flush() the buffers, then cyg_io_set_config() to  power down the  
>> drive, *then* close() ?  I assume you can't use the handle to  
>> set_config after the close(). Right?

File systems work differently. There you have a clean mount and
unmount. So i would extend the mount and umount call to call the
cyg_io_set_config() to power the device up/down. However you might
have a problem with the partition table, 

> I'm just doing the OS port & device drivers for a board that has to  
> really conserve power and thus turn devices off and on a lot. Someone  
> else will write the application, so I'm trying to make the interface as  
> simple and familiar as possible (therefore standard I/O api). It seems  
> that the eCos device API assumes that devices will be initialized then  
> stay on forever. So, any ideas are appreciated.

Well LCD devices don't always follow standard I/O. This is especially
true if you are doing a windowing driver? Or is it plain text.  And
how is the driver structured? Maybe you maintain a frame buffer in
local memory and blit it out to the LCD every so often?  With the
cyg_io_set_config() you can keep the frame buffer running all the time
and use the cyg_io_set_config() to power up/down the LCD controller
and start/stop blitting. Another cyg_io_set_config() would control the
backlight etc.

          Andrew


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