Re: [PATCH v3 6/6] iio: adc: stm32: add support for EXTI trigger

[Fabrice Gasnier <fabrice.gasnier@st.com>]

On 03/03/2017 12:45 PM, Lars-Peter Clausen wrote:
> On 02/28/2017 05:51 PM, Fabrice Gasnier wrote:
>> EXTi (external interrupt) signal can be routed internally as trigger
>> source for ADC conversions: STM32F4 ADC can use EXTI11.
>>
>> Retrieve interrupt trigger from DT, so it can be muxed into ADC IP,
>> via extsel.
> 
> Hi,
> 
> Sorry, I have some trouble understanding the specifics of this. Is EXTI a
> hardware input signal into the ADC that automatically triggers a conversion
> when asserted? If yes how is it configured which external signal is used
> here. Your bindings suggest that any GPIO can be used, but the driver only
> differentiates between EXTI on or EXTI off.
Hi Lars,

Yes, STM32 EXTI is external interrupt/event line. In case of STM32 ADC,
EXTI11 signal can be used to start a conversion. In this case, it must
be selected inside ADC IP using extsel bitfield. This EXTI11 line can
mapped from any GPIO bank A,B... line 11 (e.g. PA11 or PB11...) by using
interrupt binding.
This is why I expose this in DT.

> 
> Or is this just a software triggered conversion? The GPIO triggers a
> software interrupt routine and the interrupt routine than triggers conversion?
>