On 12/12/2012 10:28 AM, Michael Haberler wrote:
>
> Am 12.12.2012 um 10:09 schrieb Gilles Chanteperdrix:
>
>> On 12/12/2012 09:30 AM, Michael Haberler wrote:
>>>>
>>>> ...
>>>
>>> just to make sure I understand your suggestion:
>>>
>>> in kernel mode you'd suggest to go through gpiolib and use
>>> gpio_get_value/gpio_set_value if possible ?
>>>
>>> in user mode you can prepare things through sysfs but I dont see
>>> an alternative to memory-mapped register manipulation in that
>>> case if one wants to avoid system calls like
>>> read/write/open/ioctl which likely will be a dog on top of
>>> switching to secondary domain
>>
>> This happens if you put the kernel/user split in the wrong place.
>> For instance, if your GPIOS are used to implement an I2C master,
>> implementing the I2C master in user-space manipulating GPIOS in
>> kernel-space is the wrong thing to do. What you should do is
>> implement the I2C master in kernel-space, and use it either in
>> other drivers, or in user-space. This way, you will get a write for
>> a whole I2C transfer instead of a write for each GPIO change. The
>> same goes for a PWM, SPI master, RS232 why not, etc... If your
>> GPIOs are used to power on/power off some devices, then using them
>> in primary mode is probably not relevant.
>
> in that particular application, the GPIO's are used, among others,
> for generating stepper pulses, and the thread running this should be
> as fast as possible; in the RTAI/parport version of that code that's
> anywhere from 20-50uSec
>
> nothing else though except wiggling pins, in particular no
> interrupt-driven input; so I dont see any extra functionality a
> kernel driver could provide
A kernel driver provides an interface which allows changing the driver
implementation and the underlying hardware without changing either the
kernel/user interface, or the application (I did not invent that, I read
it for instance in the excellent "Linux device drivers" which I suggest
you read or reread if you missed that point), in addition to allowing
implementing for instance a reliable 50us pulse with a lower jitter. I
will stop answering your posts at this point.
--
Gilles.
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