[ECOS] Device driver open & close

[ECOS] Device driver open & close

[Frank Pagliughi]

Hey All,

Is there a mechanism by which a device driver can be notified when the 
application opens or closes the device. For example, I have an LCD in my 
system, and I would like to turn it on when the application opens the 
device and turn it off when it gets closed. Then turn it back on again 
if it gets re-opened, etc.

Thanks,
Frank

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Re: [ECOS] Device driver open & close

[Andrew Lunn]

On Mon, Aug 25, 2008 at 07:31:09PM -0400, Frank Pagliughi wrote:
> Hey All,
>
> Is there a mechanism by which a device driver can be notified when the  
> application opens or closes the device. For example, I have an LCD in my  
> system, and I would like to turn it on when the application opens the  
> device and turn it off when it gets closed. Then turn it back on again  
> if it gets re-opened, etc.

open() should result in the lookup function being called on the
device.

Close is a problem, since there is no device close function.

You might be better using cyg_io_set_config() mechanism to turn it on
and off.

    Andrew


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Re: [ECOS] Device driver open & close

[Frank Pagliughi]

Andrew Lunn wrote:
> On Mon, Aug 25, 2008 at 07:31:09PM -0400, Frank Pagliughi wrote:
>   
>> Hey All,
>>
>> Is there a mechanism by which a device driver can be notified when the  
>> application opens or closes the device. For example, I have an LCD in my  
>> system, and I would like to turn it on when the application opens the  
>> device and turn it off when it gets closed. Then turn it back on again  
>> if it gets re-opened, etc.
>>     
>
> open() should result in the lookup function being called on the
> device.
>   
This gets called for each open?
> Close is a problem, since there is no device close function.
>
> 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?

Frank

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Re: [ECOS] Device driver open & close

[Frank Pagliughi]

Frank Pagliughi wrote:
>
>
> Andrew Lunn wrote:
>> On Mon, Aug 25, 2008 at 07:31:09PM -0400, Frank Pagliughi wrote:
>>  
>>> Hey All,
>>>
>>> Is there a mechanism by which a device driver can be notified when 
>>> the  application opens or closes the device. For example, I have an 
>>> LCD in my  system, and I would like to turn it on when the 
>>> application opens the  device and turn it off when it gets closed. 
>>> Then turn it back on again  if it gets re-opened, etc.
>>>     
>>
>> open() should result in the lookup function being called on the
>> device.
>>   
> This gets called for each open?
>> Close is a problem, since there is no device close function.
>>
>> 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?
>

Oh, sorry, the disk drive is a bad example, and a whole different 
problem, I suppose. Maybe a drive can power up/down when its filesystem 
is mounted/unmounted?

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.

Thanks,
Frank

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Re: [ECOS] Device driver open & close

[Andrew Lunn]

>> 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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